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Evaluating the Reaction to a Complex Rotated Object in the American Quarter Horse (Equus caballus) - MDPI
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Article
Evaluating the Reaction to a Complex Rotated Object in the
American Quarter Horse (Equus caballus)
Megan Elizabeth Corgan, Temple Grandin *                        and Sarah Matlock

                                          Department of Animal Science, Colorado State University, Fort Collins, CO 80523, USA;
                                          mecorgan@colostate.edu (M.E.C.); sarah.matlock@colostate.edu (S.M.)
                                          * Correspondence: cheryl.miller@colostate.edu

                                          Simple Summary: Horses are prey animals and exhibit behaviors that help them adapt and survive
                                          in their environment. These reactions are often referred to as spooking and they have the potential to
                                          be dangerous to the horse, handler and rider. Spooking consists of avoidance reactions that include
                                          suddenly moving away or running away from the perceived danger. It is dangerous for both riders
                                          and horses when a horse suddenly startles. Sometimes horses do this in familiar environments
                                          because familiar objects may look different when rotated. The purpose of this study was to determine
                                          whether horses that had been habituated to a complex object (children’s playset) would react to the
                                          object as novel when rotated 90 degrees. Twenty young horses were led past the playset 15 times by
                                          a handler. Next, the rotated group was led past the rotated playset 15 times. Each time the horse
                                          was led by the object was counted as a pass. An increasing reactivity scale was used to quantify
                                          behavioral responses. Being aware of potential reactions to changes in the orientation of previously
                                          familiar objects can help keep the handler safer.

                                Abstract: It is dangerous for both riders and horses when a horse suddenly startles. Sometimes
         
                                          horses do this in familiar environments because familiar objects may look different when rotated. The
Citation: Corgan, M.E.; Grandin, T.;
                                          purpose of this study was to determine whether horses that had been habituated to a complex object
Matlock, S. Evaluating the Reaction to
                                          (children’s playset) would react to the object as novel when rotated 90 degrees. Twenty young horses
a Complex Rotated Object in the
                                          were led past the playset 15 times by a handler. Next, the rotated group was led past the rotated
American Quarter Horse (Equus
caballus). Animals 2021, 11, 1383.
                                          playset 15 times. Each time the horse was led by the object was a pass. The behavioral responses
https://doi.org/10.3390/ani11051383       observed and analyzed were ears focused on the object, nostril flares, neck raising, snort, avoid by
                                          stopping, avoid by moving feet sideways, and avoid by flight. An increasing reactivity scale was
Academic Editor: Barbara Padalino         used to quantify behavioral responses. A two-sample t-test was performed on the reactivity scores
                                          comparing the first pass by the novel object to the first pass by the rotated object. The horses in the
Received: 28 March 2021                   rotated group reacted to the rotated orientation similarly to the first exposure (p = 0.001, α < 0.05).
Accepted: 11 May 2021                     Being aware of potential reactions to changes in previously familiar environments can help keep the
Published: 13 May 2021                    handler safer.

Publisher’s Note: MDPI stays neutral      Keywords: horse; safety; training; behavior; novel object; habituation
with regard to jurisdictional claims in
published maps and institutional affil-
iations.

                                          1. Introduction
                                               Spooking was associated with 27% of horse accidents [1]. Researchers have described
                                          “spooking” as “horse reacted in fear of something, unseating the rider” [1]. Another study
Copyright: © 2021 by the authors.
                                          showed that injuries to riders were more likely to occur “when the horse behaved in an
Licensee MDPI, Basel, Switzerland.
                                          unexpected manner” [2]. Some of the more severe injuries occur when a rider falls of a
This article is an open access article
                                          horse. Data collected from hospital emergency rooms indicated that falling off a horse
distributed under the terms and
                                          resulted in more injuries than injuries that occurred when the rider was not mounted [3].
conditions of the Creative Commons
Attribution (CC BY) license (https://
                                          Another study showed that “danger to the rider increases as the horse’s speed increases” [4].
creativecommons.org/licenses/by/
                                          When riders fall of a horse, their head is more likely to be injured compared to other parts
4.0/).
                                          of the body [5]. Riders have reported that sometimes they do not know what caused their

Animals 2021, 11, 1383. https://doi.org/10.3390/ani11051383                                                 https://www.mdpi.com/journal/animals
Evaluating the Reaction to a Complex Rotated Object in the American Quarter Horse (Equus caballus) - MDPI
Animals 2021, 11, 1383                                                                                            2 of 9

                         horse to spook. Experienced horse trainers know that it is important to habituate young
                         horses to new things in their environment. One study showed that gradually desensitizing
                         horses to stimuli such as a moving white nylon bag had fewer flight responses than horses
                         where it was suddenly introduced [6]. Several studies have also indicated that a sudden
                         stimuli such as an umbrella that opens suddenly can startle a horse [7–11]. A sudden novel
                         stimulus such as a waving flag or a bell will raise a horse’s heart rate [12]. Researchers
                         have also reported the intensity of a horse’s reaction was influenced by horse genetics [13].
                         Sudden novel stimuli will startle many different species of animals [14]. The dangerous
                         and usually unexpected “spook” reaction is likely to be a startle response.
                               A review of the horse behavior literature showed that there are different ways that
                         horses are introduced to new objects. They consist of voluntary approach in an open field,
                         led towards the object, or ridden toward the object [15–17]. Open field tests are usually
                         conducted in an arena. In these experiments a free moving horse is allowed to voluntarily
                         approach novel objects [15]. In many of these studies the horse learns to associate a
                         particular novel object with a food reward [18,19]. These studies are extremely useful for
                         the study of horse cognition and learning. However they do not provide information on
                         the conditions that may cause a dangerous “spook” reaction that could seriously injure a
                         rider. One study showed that horses that were more willing to investigate a novel object
                         were able to learn more quickly [20]. There may be differences in a horses reaction to a
                         novel object when the way it is presented is changed. Research has shown that a horses
                         reaction to a novel object is different during a voluntary approach compared to being led
                         or ridden [17]. The authors found that when including a rider in temperament tests and
                         performance tests, results were more reliable and repeatable. When positive reinforcement
                         such as food is used, horses are able to choose the correct object and be presented with a
                         reward. This type of learning and test does not often include a handler and is referred to as
                         discrimination [18].
                               The purpose of this research was to conduct a study to identify a possible situation
                         where a large complex novel object may have the potential to cause a serious horse accident.
                         The object we chose was a child’s colored plastic playset with a small slide and swing. It
                         is a large object and large objects may be more frightening stimulus compared to smaller
                         objects [21]. The playset is an object that a horse could possibly see during riding near
                         residences. It is known that horses can learn to discriminate between different colors and
                         shapes [18,22]. In our experiment, no attempt was made to control for color or shape, but a
                         playset was chosen that had approximately the same dimensions when it was rotated.
                               The purpose of this preliminary study was to determine if a habituated horse may
                         react differently when the playset was rotated. Both its shape and color would change. A
                         non-voluntary approach was used. All horses were led at a walk for both habituation and
                         the test after the playset was rotated. For safety reasons, we conducted all experiments at a
                         walk and measured behavioral reactions used by Leiner and Fendt [7]. Their study may
                         provide insights into a situation that might trigger dangerous “spooking”. If the rotated
                         playset is associated with increased mild behavioral reactions when a horse is being led
                         towards it, there is the possibility that it might trigger a more dangerous sudden reaction
                         if a horse and rider was trotting towards it. A high speed study would be too dangerous
                         and would be unethical. This study may help identify one cause of spooking when a rider
                         is not able to identify an obvious possible trigger. It will also provide a starting point for
                         further studies into horse perception.

                         2. Materials and Methods
                              The sample population consisted of twenty-two 2 and 3-year-old American Quarter
                         Horse horses (15 fillies and seven gelded colts) in a university horse training program. The
                         horses had 4 months of handling training at the time of this study, all trained at the same
                         place. The horses were taught using methods of pressure and release training to halter,
                         lead, lunge, and acclimate to being groomed and handled. Of the twenty-two horses, one
                         posed a safety concern for the research handlers by its continued attempt to pull away and
Evaluating the Reaction to a Complex Rotated Object in the American Quarter Horse (Equus caballus) - MDPI
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 Animals 2021, 11, x                                                                                                                                     3 of 10
   Animals 2021, 11, 1383                                                                                                                                   3 of 9
                                       halter, lead, lunge, and acclimate to being groomed and handled. Of the twenty-two
                                       horses, one posed a safety concern for the research handlers by its continued attempt to
                                       halter, lead, lunge, and acclimate to being groomed and handled. Of the twenty-two
                                       pull away and was excluded from the study. Another horse was removed from the study
                                       horses,
                                         was      one posed
                                                excluded         a safety
                                                              from          concern
                                                                     theissues.
                                                                          study.       for thehorse
                                                                                   Another       researchwas  handlers
                                                                                                               removed     by
                                                                                                                            fromits continued
                                                                                                                                    the            attempt   4to
                                       on
                                       pull
                                           day
                                             away
                                                  4 for
                                                      and
                                                          soundness
                                                            was   excluded
                                                                                  Twenty
                                                                               from   the
                                                                                              horses
                                                                                          study.
                                                                                                         continued
                                                                                                    Another      horse
                                                                                                                        through
                                                                                                                         was
                                                                                                                                     thestudy
                                                                                                                                removed
                                                                                                                                           entire
                                                                                                                                             from
                                                                                                                                                   on  day (n
                                                                                                                                                    study
                                                                                                                                                     the study
                                                                                                                                                               for
                                                                                                                                                                 = 20).
                                         soundness
                                       All  horses       issues.
                                                        were       Twenty
                                                                housed    at horses
                                                                              the      continued
                                                                                   Colorado      Statethrough     the
                                                                                                          University   entire
                                                                                                                          Equine study   (n  =
                                                                                                                                      Teaching  20).  All
                                                                                                                                                    and    horses
                                                                                                                                                           Research
                                       onwere
                                           day housed
                                                 4 for soundness       issues. Twenty
                                                            at the Colorado      State     horses continued
                                                                                        University      Equine      throughand  the Research
                                                                                                                                     entire study      (n = (CSU
                                                                                                                                                             20).
                                       Center
                                       All  horses(CSUwere ETRC)
                                                              housed in at
                                                                         outdoor
                                                                            the      pens
                                                                                 Colorado   with
                                                                                              State      libitumTeaching
                                                                                                    adUniversity    water
                                                                                                                      Equine and    access to
                                                                                                                                 Teaching      and
                                                                                                                                                  Center
                                                                                                                                                  shelter.
                                                                                                                                                      ResearchHorses
                                         ETRC) in outdoor pens with ad libitum water and access to shelter. Horses were fed a mix
                                       were fed
                                       Center       a mix
                                                 (CSU         of grass   and alfalfa     hay once      per day     on a feed bunk.
                                         of grass   andETRC)
                                                           alfalfainhayoutdoor
                                                                          once perpensdaywith
                                                                                           on aad    libitum
                                                                                                  feed   bunk.water and access to shelter. Horses
                                       were fedThe   test
                                                   a mix   environment       was    an  alley  (4.57    meters    wide)
                                                                                                                     feedinbunk.
                                                                                                                               an indoor horse barn in front
                                                The    test of  grass and alfalfa
                                                             environment       was an hayalley
                                                                                           once(4.57
                                                                                                   per day     on awide)
                                                                                                          meters             in an indoor horse barn in
                                       offront
                                           empty
                                             The      stalls
                                                 oftest
                                                    empty
                                                               with
                                                          environment the  doors
                                                               stalls withwasthean
                                                                                    closed.   The
                                                                                     alleyclosed.
                                                                                  doors
                                                                                                     barn
                                                                                            (4.57 meters    had
                                                                                                             wide)
                                                                                                      The barn
                                                                                                                   concrete
                                                                                                                      in an
                                                                                                                    had
                                                                                                                                 flooring
                                                                                                                              indoor
                                                                                                                          concrete      horse and
                                                                                                                                       flooring barn electric  lights
                                                                                                                                                   andinelectric
                                                                                                                                                           front
                                       above
                                       of empty
                                         lights  the
                                                  abovealleyway.
                                                    stalls   with
                                                           the       Thedoors
                                                                    the
                                                                alleyway.  horses   were The
                                                                             Theclosed.
                                                                                   horses   led
                                                                                            were in
                                                                                                 barnthrough
                                                                                                    led   had
                                                                                                         in       the entrance,
                                                                                                                concrete
                                                                                                            through     theflooring   walked
                                                                                                                              entrance, and      down
                                                                                                                                               electric
                                                                                                                                            walked        the the
                                                                                                                                                         lights
                                                                                                                                                       down     alley-
                                       way,
                                       above   past
                                                the    the  novel
                                                     alleyway.       object
                                                                   The        and
                                                                         horses      led
                                                                                  were    out
                                                                                         led  inof  the
                                                                                                 through  testthearea  through
                                                                                                                   entrance,         the
                                                                                                                                 walked
                                         alleyway, past the novel object and led out of the test area through the exit (Figure 1). Two     exit
                                                                                                                                            down (Figure
                                                                                                                                                     the     1).
                                                                                                                                                          alley-  Two
                                       Hero
                                       way,
                                         Hero  55video
                                               pastvideo   cameras
                                                      the novel
                                                            cameras    (GoPro,
                                                                   object   and led
                                                                        (GoPro,    Sanout
                                                                                   San   Mateo,
                                                                                             of the
                                                                                        Mateo,     CA,
                                                                                                   CA, testUSA)    were
                                                                                                            areawere
                                                                                                         USA)      through placed
                                                                                                                         placed       in
                                                                                                                                       thethe
                                                                                                                                theinexit      test
                                                                                                                                            (Figure
                                                                                                                                            test      environment
                                                                                                                                                       1). Two
                                                                                                                                                  environment
                                       Hero
                                       for     5 video
                                         forlater
                                              later       cameras of
                                                   observation
                                                     observation      (GoPro,    San Mateo,
                                                                      of behavioral
                                                                         behavioral             CA, USA) were placed in the test environment
                                                                                        responses.
                                                                                        responses.
                                       for later observation of behavioral responses.

         Figure
      Figure
       Figure 1.1.1.
                  TheThe
                   The    test
                       test
                        test   areaconsisted
                             area    consisted
                                   consisted  ofofGoPros
                                             of    GoPros
                                                  GoPros ( ((      ) and) the novel
                                                                          andthe
                                                                      ) and    the  object
                                                                                   novel
                                                                                 novel     placed
                                                                                         object
                                                                                       object     during
                                                                                                 placed
                                                                                              placed     habituation
                                                                                                        during
                                                                                                     during          to the
                                                                                                               habituation
                                                                                                            habituation     novel
                                                                                                                                theobject
                                                                                                                             to novel
                                                                                                                        to the      novel and
                                                                                                                                           object
                                                                                                                                      object
       and
      and   rotation
           rotation
         rotation     days.
                      days.
                   days.

                                               Thenovel
                                             The
                                              The   novelobject
                                                   novel  objectwas
                                                          object   wasa aachildren’s
                                                                  was       children’s
                                                                            children’s   plastic
                                                                                       plastic
                                                                                          plasticplayset
                                                                                               playset
                                                                                                  playset  (Little
                                                                                                         (Little   Tikes
                                                                                                                 Tikes
                                                                                                             (Little      Hide
                                                                                                                         Hide
                                                                                                                     Tikes      and
                                                                                                                               and
                                                                                                                            Hide      Seek
                                                                                                                                    Seek
                                                                                                                                   and      Climber
                                                                                                                                          Climber
                                                                                                                                        Seek   Climber
                                         and
                                       and     Swing-Brown
                                            Swing-Brown        and
                                                             and    Tan)
                                                                   Tan)      (Table
                                                                           (Table   1).
                                                                                   1).   The
                                                                                        The   object
                                                                                             object   was
                                                                                                     was     134.62
                                                                                                           134.62  l l
                                                                                                                     ×
                                       and Swing-Brown and Tan) (Table 1). The object was 134.62 l × 132.08 w × 104.14 × 132.08
                                                                                                                        132.08  ww× ×  104.14
                                                                                                                                     104.14  hh  cm.
                                                                                                                                               cm.h cm.
                                         This
                                       This    object was  used   because,     in both   orientations,   its outer   dimensions    are similar.  The
                                       This object
                                              objectwas
                                                     wasused
                                                           usedbecause,
                                                                  because,ininbothboth orientations,
                                                                                          orientations,its its
                                                                                                           outer  dimensions
                                                                                                               outer   dimensionsare similar.  The The
                                                                                                                                      are similar.
                                         playset hada adifferent
                                       playset           different shapewhen   whenrotated
                                                                                       rotatedninety
                                                                                                ninetydegrees.
                                                                                                         degrees.RopeRopehalters
                                                                                                                            halterswith
                                                                                                                                     with2 2mmlead
                                                                                                                                                lead
                                       playset had
                                                 had a differentshape
                                                                    shape when          rotated ninety     degrees. Rope      halters with    2 m lead
                                         ropes
                                       ropes     were used  to  lead the    young   horses   past  the playset.
                                       ropeswere
                                               wereused
                                                     usedtotolead
                                                               leadthe
                                                                     theyoung
                                                                            young horses
                                                                                    horses past  thethe
                                                                                              past   playset.
                                                                                                         playset.
                                               On day 1–3 of the study (habituation to the test area) (Table 1), the horses were led
                                         through the test area five passes each day without the novel object to habituate the horses
                                         to the test area. Each time a horse was led past the object was counted as a pass. The
                                         horses were given 15 total passes through the test area based on Christensen et al. [15]. The
                                         authors found that horses needed 4–13 exposures before meeting habituation criterion.
                                               On day 4, the novel object was placed in the test area in the original position. Days
                                         4–6 of the study (habituation to the novel object) consisted of the same procedure for the
                                         first three days with the novel object in its original position (Table 1). Each horse passed
                                         the original position of the object fifteen times over three days.
                                               To assess the effect of object rotation on the horses’ behavior, the horses were random-
                                         ized into a control group and a rotated group. On days 7–9 (test days), the control group
                                         had five passes each day through the test area, with the novel object in the original position
                                         (Table 1). The control group passed the original position of the object fifteen times over the
                                         three days. The rotated group was led through the test environment for five passes each
                                         day with the novel object rotated 90 degrees clockwise (Table 1). The rotated group passed
                                         the rotated position of the object fifteen times over the three days.
Table 1. TestingTable
                                            Procedure:
                                                  1. Testing
                                                         Outline
                                                             Procedure:
                                                                 of testing
                                                                         Outline
                                                                            procedure
                                                                                 of testing
                                                                                       to provide
                                                                                            procedure
                                                                                                  details
                                                                                                      to provide
                                                                                                          of the Control
                                                                                                                  detailsand
                                                                                                                          of the
                                                                                                                              Ro-Control and Ro-
nimals 2021, 11, x         tated group procedures.
                                           tated group procedures.                                                                  4 of 10

                                                                                      Control and Rotated  Controlgroups
                                                                                                                     and Rotated groups
           Animals 2021, 11, 1383             Habituation to test
                                                               Habituation
                                                                   area       to test area 5 passes each day     5 passes each day                    4 of 9
                            DaysTable
                                  1–3 1. Testing
                                            Days 1–3
                                                  Procedure: Outline of testing procedure to provide details of the Control and Ro-
                                                (novel object absent)
                                                                (novel object absent)          15 total passes 15 total passes
                                 tated group procedures.
                                                                               test area (Figuretest1) without
                                                                                                         area (Figure
                                                                                                                   novel1)object
                                                                                                                           without novel object
                                                                                      ControlControl
                                                                                                 and Rotated
                                                                                                           Controlgroups
                                                                                                                     and Rotated
                                                                                                           and Rotated     groups groups
                Table 1. Testing Procedure: Outline ofHabituation
                                                        testing procedure   to provide details
                                                                    to test area                    of 5the
                                                                                             5 passes    eachControl
                                                                                                               day
                                                                                                          passes 5each and
                                                                                                                         dayRotated
                                                                                                                    passes  each daygroup procedures.
                                     Days 1–3
                                                        (novel object absent)                  15 total 15passes
                                                                                                             total 15  total passes
                                                                                                                    passes
                                                                                                Control and Rotated groups
                                                                          test area (Figure
                                                                                         test test
                                                                                               1) with
                                                                                              area area   novel
                                                                                                          (Figure
                                                                                                    (Figure    1) object
                                                                                                                    1) with
                                                                                                                  withoutin novel
                                                                                                                            original
                                                                                                                             novelobject
                                                                                                                                   object in original
                                Habituation to test area                                               5 passes    eachposition
                                                                                                                         day
              Days 1–3                                                                             position
                                                                                                Control    and   Rotated   groups
                                  (novel object absent)                                                   15 total passes
                                                                                                       5 passes each day
                                                                                         test area (Figure 1) without novel object
                                              Habituation to the
                                                               Habituation
                                                                  novel      to the novel Control15and       total passes
                                                                                                                 Rotated   groupsin original
                            Days 4–6        Days 4–6                                test area  (Figure    1) with   novel object
                                                        object           object
                                                                                                              position
                                                                                                       5 passes    each day
                                                                                                          15 total passes
                                                                               test area (Figure 1) with novel object in original position
                                                      Habituation to the novel
                                     Days 4–6
              Days 4–6      Habituation to the novel object object

                               Days 7–9               Days 7–9Test days               Test daysControl group Control group  Rotated group Rotated group
                                                                                            5 passes each day 5 passes each   day each day
                                                                                                                          5 passes          5 passes each day
                                                                                         test area (Figuretest
                                                                                                            1) with
                                                                                                               area (Figure
                                                                                                                     test area1)(Figure
                                                                                                                                 with test
                                                                                                                                         1) with
                                                                                                                                             area (Figure 1) with
              Days 7–9                         Test days                                       Control
                                                                                          object        group
                                                                                                 in originalobject
                                                                                                              posi-in original
                                                                                                                       object inposi-
                                                                                                                                 rotatedobjectRotated
                                                                                                                                           posi-       group
                                                                                                                                                 in rotated  posi-
                                          Days 7–9                            Test days      5 passes  each
                                                                                                    tion     day
                                                                                                        Control group  tion      tion       5  passes
                                                                                                                                     Rotated group    each
                                                                                                                                                    tion    day
                                                                                    test area (Figure5 1) with each
                                                                                                        passes  objectday
                                                                                                                        in        5test area each
                                                                                                                                     passes   (Figure
                                                                                                                                                   day1) with object in
                                                                                             original  position                              rotated
                                                                                                  test area (Figure 1) with test area (Figure 1) with position
                                                                                                   object in original posi- object in rotated posi-
                                                                                                             tion                         tion

                                                           Two handlers were used and both led the horses at a slow walk. Each handler had
                                 On day 1–3 an    ofOn the  day
                                                        equal study1–3(habituation
                                                                  number   of the     studyto(habituation
                                                                                 of horses           the test area)
                                                                                                   randomly               to (Table
                                                                                                                       assignedthe test    1),area)
                                                                                                                                        from     the
                                                                                                                                                   both horses
                                                                                                                                                        (Table     1),
                                                                                                                                                                   were
                                                                                                                                                            the control theled
                                                                                                                                                                             horses
                                                                                                                                                                             and       were group.
                                                                                                                                                                                   rotated     led
                           through the test  through
                                                area
                                                  Eachfive  thepasses
                                                            horse test
                                                                     was areaeach
                                                                              ledfive
                                                                                    atday
                                                                                        apasses
                                                                                              without
                                                                                           walk       eachthe
                                                                                                     through    day novel
                                                                                                                     thewithout
                                                                                                                            testobject
                                                                                                                                   areathetobynovel
                                                                                                                                                habituateobjectthe
                                                                                                                                                  the same         to horses
                                                                                                                                                                       habituate
                                                                                                                                                                 handler     for thethe    horses
                                                                                                                                                                                       entire   study.
                           to the test area.toEach
                                                the    test
                                                        time   area.
                                                                 a  horse
                                                                       Each    was
                                                                                 time leda   horse
                                                                                             past    thewas object
                                                                                                                led    past
                                                                                                                        was     the
                                                                                                                                 counted
                                                                                                                                      object
                                                 The handlers wore the same clothes every day (black overalls, jacket, hat and black boots).    aswas
                                                                                                                                                    a  pass.
                                                                                                                                                         countedThe    horses
                                                                                                                                                                       as a pass.   The    horses
                           were given 15were  total
                                                 The  given
                                                       passes
                                                         handlers15through
                                                                      total
                                                                          were  passes
                                                                                   the    test
                                                                                   instructedthrough
                                                                                                 area  tobased
                                                                                                             the test
                                                                                                            walk       onarea
                                                                                                                      the    Christensen
                                                                                                                             horse   based
                                                                                                                                       with on    a etChristensen
                                                                                                                                                    leadal. rope
                                                                                                                                                             [15]. through
                                                                                                                                                                     Theetau-al. the
                                                                                                                                                                                  [15].  The au-
                                                                                                                                                                                      center   of the
                           thors foundOn   thatday
                                             thors
                                                 horses1–3
                                                       found   of  the
                                                              needed
                                                                  that    study
                                                                          horses
                                                                            4–13     (habituation
                                                                                     exposures
                                                                                       needed        4–13    to
                                                                                                         before   the
                                                                                                               exposures test
                                                                                                                     meeting      area)
                                                                                                                                   before  (Table
                                                                                                                                      habituation
                                                  alley (1 m away from the object), and move with the horse, only stopping or turning when     meeting  1),  the   horses
                                                                                                                                                           criterion.
                                                                                                                                                               habituation   were    led
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                                   group passed the rotated position of the object fifteen times over the three days.
                                          Two handlers were used and both led the horses at a slow walk. Each handler had
                                   an equal number of horses randomly assigned from both the control and rotated group.
                                   Each horse was led at a walk through the test area by the same handler for the entire study.
Animals 2021, 11, 1383                                                                                                               5 of 9

                                Table 2. Behavioral responses and definitions used for behavioral analysis.

                                                  Definitions of Behavioral Responses
      Behavioral Responses                                                       Definition
    ears focused on the object                                    ears are pointed toward the novel object
           nostril flares                                       nostrils overly expanded (nose elongation)
           neck raising                               neck raised above normal headset and/or neck muscles tense
             snorting                                                   “short powerful exhale” [23]
            avoid stop                                       avoiding the object by stopping, feet stop moving
            avoid side                            avoiding the object by evasive steps to the side, away from the object
            avoid back                                 avoiding the object by evasive steps backwards, backing up
           avoid flight                   avoiding the object by jumping away in a sudden movement, feet moving faster a walk

                                    Table 3. Reaction Scale used to quantify behavioral responses (adapted from Christensen et al. [15]).

                                                        Score 0–3                              Behavioral Responses Observed
                                                            0                                   No behavioral signs observed
                                                            1                           Ears focused, nostril flares, and/or neck raising
                                                            2                                    Snorting and/or avoid stop
                                                            3                                 Avoid side, avoid back, avoid flight

                                         To assess whether the horses’ behavior was affected by the object rotation we compared
                                    difference in the reaction score per individual horse using a two-sample t-test (α < 0.05) (R
                                    with R Studio, PBC, Boston, MA, USA). Christensen et al. and Tidyverse (www.tidyverse.
                                    org, accessed on 28 March 2021) was used for the figures [15,24,25]. This test was done
                                    for each pass 1–15 comparing the corresponding passes from the original position to the
                                    rotated position.

              Animals 2021, 11, x   3. Results                                                                                                   6o

                                          The control and rotated group showed significant differences between the change in
                                    reaction score from the first pass by the novel object to the first pass on the Test days (t-test
                                    p-value = 0.001)   (Figure
                                                 reacted        2). Horses
                                                          similarly   on the that
                                                                             first reacted
                                                                                   pass by to
                                                                                            thethe novel position
                                                                                                 rotated   object inof
                                                                                                                     the
                                                                                                                       theRotated group,
                                                                                                                           object as they did on
                                    reacted similarly    on the first pass by  the
                                                 initial pass by the novel object.  rotated position   of the object  as they did on  the
                                    initial pass by the novel object.

                                    Figure 2. Boxplot of differences in Reaction Score for pass 1 by the novel object to pass 1 by the
                    Figure 2. Boxplot of differences in Reaction Score for pass 1 by the novel object to pass 1 by the rotated object. The Control
                                    rotated object. The Control group mean (bold line) showed a decrease in reaction. The Rotated group
                    group mean (bold line) showed a decrease in reaction. The Rotated group mean showed no change in reaction. There was
                                    mean showed no change in reaction. There was a significant difference between the means of the
                    a significant difference between the means of the two groups.
                                    two groups.
                                                      Passes 1–4 after rotation in the rotated group showed a significant difference betwe
                                                 the two groups change in reaction (p-values = 0.001, 0.010, 0.004, 0.001). After pass 4
                                                 the rotated object, there was little significant difference between the rotated and cont
                                                 groups (p-values > 0.05). As noted in Table 4, some later passes also showed signific
                                                 differences in the change in reaction between the two groups (Passes 1–4, 8, 9, 12: p-va
Animals 2021, 11, 1383                                                                                                               6 of 9

                                         Passes 1–4 after rotation in the rotated group showed a significant difference between
                                    the two groups change in reaction (p-values = 0.001, 0.010, 0.004, 0.001). After pass 4 by the
                                    rotated object, there was little significant difference between the rotated and control groups
                                    (p-values > 0.05). As noted in Table 4, some later passes also showed significant differences
                                    in the change in reaction between the two groups (Passes 1–4, 8, 9, 12: p-value > 0.05).
                                    Figures 2 and 3 show the significance in the change in reactions for the rotated group when
                                    the horses were exposed to the rotated object.

                                    Table 4. Values for differences in reaction score for corresponding passes 1–15 by the novel object to
                                    rotated object.

                                                               Control                                Rotated
                                       Pass #       Mean         Min.         Max.        Mean         Min.         Max.       p-Value
                                          1        −1.75          −3            0         0.083         −2            2          0.001
                                          2        −0.875         −2            0          0.25         −1            2          0.010
                                          3        −0.875         −2            0         0.167         −1            1          0.004
                                          4         −1            −2            0         0.333         −1            1          0.001
                                          5        −0.375         −2            1         -0.083        −2            0          0.312
                                          6        −0.375         −1            0          -0.25        −1            1          0.719
                                          7         −0.5          −2            0         0.167         −1            1          0.062
                                          8         −1            −2            0         0.333         −1            2          0.005
                                          9        −0.875         −2            0         0.583         −2            2          0.002
                                         10        −0.125         −1            1         0.167         −1            2          0.537
                                         11          0            0             0         0.167         −2            2          0.656
                                         12        0.125          −1            1         -0.333        −1            0          0.010
                                         13        −0.125         −1            1         0.333         −2            1          0.226
              Animals 2021, 11, x                                                                                                             7o
                                         14        −0.25          −1            2         0.083         −2            2          0.554
                                         15          0            −1            1         -0.167        −2            2          0.700

                                   Figure 3. Graph of reaction scores from pass 1–30 for the control and rotated groups. The colored
                    Figure 3. Graph of reaction scores from pass 1–30 for the control and rotated groups. The colored triangles indicate indi-
                                   triangles indicate individual horses’ reactivity scores. The colored lines depict mean reaction score by
                    vidual horses’ reactivity scores. The colored lines depict mean reaction score by group over passes (control = red, rotated
                    = blue).       group over passes (control = red, rotated = blue).

                                    4. Discussion
                                               4. Discussion
                                         When a previously familiar complex novel object is rotated, the rotated object may
                                                    When ato
                                    cause reactions similar   previously
                                                                the initialfamiliar
                                                                             exposurecomplex
                                                                                        to the novel
                                                                                               novel object
                                                                                                      object.is This
                                                                                                                rotated, the rotated
                                                                                                                     confirms  what object m
                                    handlers and riders have described anecdotally. Understanding horses’ reaction to a what h
                                               cause  reactions similar  to the initial exposure to the novel   object. This confirms
                                               dlers and riders have described anecdotally. Understanding horses’ reaction to a rota
                                               object is important for the safety of riders and handlers. If handlers expect horses no
                                               react to subtle changes in a familiar environment, they are less prepared for a horse spo
                                               ing which could lead to an accident. Additionally, studies have shown that investigat
                                               behavior is correlated with learning [20]. Allowing a horse to investigate and become
Animals 2021, 11, 1383                                                                                            7 of 9

                         rotated object is important for the safety of riders and handlers. If handlers expect horses
                         not to react to subtle changes in a familiar environment, they are less prepared for a
                         horse spooking which could lead to an accident. Additionally, studies have shown that
                         investigative behavior is correlated with learning [20]. Allowing a horse to investigate
                         and become familiar with all orientations of an object can help to avoid spooking. Future
                         studies are needed to evaluate if allowing a horse to fully investigate a novel object will
                         help with habituation and decrease spooking.
                              As shown in Figure 3, there was a decline in the horses’ reactions with each successive
                         pass by the rotated object. Table 4 shows the significant decrease in the horses’ reaction
                         to the object with each successive pass, for the first four passes. After pass 4, the changes
                         in reactions between the rotated and non-rotated groups seem to be less consistent. This
                         inconsistency in changes in reactions between the two groups shows the unpredictable
                         nature of the horse [26]. Even subtle changes to a familiar object can cause horses to react
                         again. These subtle changes can cause the horse to need more exposure until they are
                         habituated or until no reactions are shown again. Handlers need to be aware of this for
                         safety of themselves and the horses.
                              This study shows that despite findings from previous research [19], horses may
                         not recognize different orientations of previously familiar objects, when being led by a
                         handler. While assumptions cannot be made about the horse’s recognition of the rotated
                         object from the present study, there is an obvious reaction to the rotated object. This
                         reaction is important to note and important for anyone handling horses to be aware of.
                         There are possible differences in personality and reactivity by breed [27]. The traits that
                         showed the most variability between breeds were excitability and anxiousness [27]. This is
                         thought to be because of the purpose each breed has been bred for over time. For example,
                         Thoroughbreds tend to show a bigger flight response because they are bred to race and
                         are expected to leave the gate quickly [28]. Age has also been shown to have an effect
                         on reactivity. In a study comparing horses ranging in age from two months to two years,
                         younger horses were more reactive [29].
                              Training methodologies are worth further exploration when researching equine percep-
                         tion of novel objects. Humans can have an impact on how the horse reacts and behaves [16].
                         There may be a difference between a voluntary approach, as compared to being led by
                         a handler. Marsboll and Christensen [30] and Hartmann et al. [31] found that a familiar
                         handler can have a calming effect on the horses response to a novel object as well as a
                         change in fear response. The present study used unknown handlers to evaluate how
                         horses will react to a rotated object with a handler. Christensen et al. [20] showed that
                         fearfulness was not correlated with learning, whereas investigative behavior was correlated
                         with learning. While their study did not use handlers, the present study allowed some
                         investigative behavior and kept the handler involved, creating a more practical scenario.
                         The present study did not use food or positive reinforcement when evaluating recognition
                         or reactivity, as compared to [19]. Using food as a reinforcement in training is similar to
                         using latency to eat in research. It is important to note, that most trainers do not use food
                         as reinforcement in their training.
                              The purpose of this study was to evaluate how horses being led and habituated to a
                         previously familiar complex object would react after it was rotated ninety degrees. This
                         study showed that horses’ reaction to a rotated orientation of a familiar complex object was
                         similar to its reaction when it first saw it.

                         5. Conclusions
                              Horses may have a greater reaction to new orientations of previously familiar objects.
                         This may cause accidents that lead to injury of the horse or handler. If handlers and
                         riders can be prepared for how a horse may react, they may be able to help reduce risk by
                         adjusting training methods to allow for investigation of all sides of an object. Additionally,
                         while horses show a decrease in reactions to novel objects and novel orientations of familiar
                         objects, there is the possibility for reactions during habituation. Further research needs to
Animals 2021, 11, 1383                                                                                                                8 of 9

                                   be conducted to evaluate how different methods of handling and training affect the horses’
                                   reaction to changes in their environment.

                                   Author Contributions: Conceptualization, M.E.C., T.G., and S.M.; methodology, M.E.C. and T.G.;
                                   formal analysis, M.E.C.; investigation, M.E.C. and S.M.; resources, M.E.C. and T.G.; data curation,
                                   M.E.C.; writing—original draft preparation, M.E.C.; writing—review and editing, M.E.C., T.G., and
                                   S.M.; visualization, M.E.C., T.G., and S.M.; project administration, M.E.C.; funding acquisition, T.G.
                                   All authors have read and agreed to the published version of the manuscript.
                                   Funding: This research was funded by Grandin Livestock Handling Systems, Inc., Fort Collins,
                                   CO 80523, USA.
                                   Institutional Review Board Statement: This study received ethical approved by the Colorado State
                                   University Animal Care and Use Committee [IACUC #: 1349].
                                   Informed Consent Statement: No applicable because no human subjects were involved.
                                   Data Availability Statement: The data presented in this study are openly available in FigShare at
                                   [10.6084/m9.figshare.14256512.v1].
                                   Acknowledgments: The authors would like to thank John Snyder and the Legends of Ranching
                                   Program for use of the horses in the study and the Equine Teaching and Research Center for use of
                                   the facility. The authors would also like to thank Ben Sharp for assistance in statistical analysis.
                                   Conflicts of Interest: The authors declare no conflict of interest.

References
1.    Camargo, F.; Gombeski, W.R.; Barger, P.; Jehlik, C.; Wiemers, H.; Mead, J.; Lawyer, A.; Gonzalez-Redondo, P. Horse-related
      injuries: Causes, preventability, and where educational efforts should be focused. Cogent Food Ag. 2018, 4, 14322168. [CrossRef]
2.    Meredith, L.; Ekman, R.; Brolin, K. Epidemiology of Equestrian Accidents: A Literature Review. Internet J. Allied Health Sci. Pract.
      2018, 17, 9.
3.    Acton, A.S.; Gaw, C.E.; Chounthirath, T.; Smith, G.A. Nonfatal horse-related injuries treated in emergency departments in the
      United States, 1990–2017. Am. J. Emerg. Med. 2020, 38, 1062–1068. [CrossRef] [PubMed]
4.    Hawson, L.A.; McLean, A.N.; McGreevy, P.D. The roles of equine ethology and applied learning theory in horse related human
      injuries. J. Vet. Behav. 2010, 5, 324–338. [CrossRef]
5.    Krüger, L.; Hohberg, M.; Lehmann, W.; Dresing, K. Assesing the risk for major injuries in equestrian sports. BMJ Open Sport Exerc.
      Med. 2010, 4, 1–9. [CrossRef]
6.    Christensen, J.W.; Rundgren, M.; Olsson, K. Training methods for horses: Habituation to a frightening stimulus. Eq. Vet. J. 2010,
      38, 439–443. [CrossRef]
7.    Leiner, L.; Fendt, M. Behavioural fear and heart rate responses of horses after exposure to novel objects: Effects of habituation.
      Appl. Anim. Behav. Sci. 2011, 131, 104–109. [CrossRef]
8.    Dai, F.; Heinzl, N.H.C.E.U.I.; Costa, E.D.; Canali, E.; Minero, M. Validation of a fear test in sport horses using infrared thermogra-
      phy. J. Vet. Behav. 2015, 10, 128–138. [CrossRef]
9.    Górecka-Bruzda, A.; Jastrzebska, E.; Sosnowska, Z.; Jaworksi, Z.; Jezierski, T.; Chruszczewski, M.H. Reactivity to humans and
      fearfulness tests: Field validation in Polish Cold Blood Horses. Appl. Anim. Behav. Sci. 2011, 133, 207–215. [CrossRef]
10.   Scopa, C.; Palagi, E.; Sighieri, C.; Baragli, P. Physiological outcomes of calming behaviors support the resilience hypothesis in
      horses. Sci. Rep. 2018, 8, 1–9. [CrossRef]
11.   Lansade, L.; Bouissou, M.F.; Erhard, H.W. Fearfulness in horses: A temerament trait stable across time and situation. Appl. Anim.
      Behav. Sci. 2008, 115, 182–200. [CrossRef]
12.   Noble, G.K.; Blackshaw, K.L.; Cowling, A.; Harris, P.A.; Sillence, M.N. An objective measure of reactive behavior in horses. Appl.
      Anim. Behav. Sci. 2013, 144, 121–129. [CrossRef]
13.   Borstel, U.K.v.; Duncan, I.J.H.; Lundin, M.C.; Keeling, L.J. Fear reactions in trained and untrained horses from dressage and
      show-jumping breeding lines. Appl. Anim. Behav. Sci. 2010, 125, 124–131. [CrossRef]
14.   King, T.; Hemsworth, P.H.; Coleman, G.J. Fear of novel and startling stimuli in domestic dogs. Appl. Anim. Behav. Sci. 2003,
      82, 45–64. [CrossRef]
15.   Christensen, J.W.; Malmkvist, J.; Nielsen, B.L.; Keeling, L.J. Effects of a calm companion on fear reactions in naive test horses.
      Equine Vet. J. 2008, 40, 46–50. [CrossRef]
16.   Visser, E.K.; van Reenen, C.G.; van der Werf, J.T.; Schilder, M.B.H.; Knaap, J.H.; Barneveld, A.; Blokuis, H.J. Heart rate and heart
      rate variability during a novel object test and a handling test in young horses. Physio. Behav. 2002, 76, 289–296. [CrossRef]
17.   Borstel, U.K.v.; Pirsich, W.; Gauly, M.; Bruns, E. Repeatability and reliability of scores from ridden temperament tests conducted
      during performance tests. Appl. Anim. Behav. Sci. 2012, 139, 251–263. [CrossRef]
Animals 2021, 11, 1383                                                                                                                 9 of 9

18.   Hanggi, E.B. Discrimination learning based on relative size concepts in horses (Equus caballus). Appl. Anim. Behav. Sci. 2003,
      83, 201–213. [CrossRef]
19.   Hanggii, E.B. Rotated object recognition in four domestic horses (Equus caballus). J. Equine Vet. Sci. 2010, 30, 175–186. [CrossRef]
20.   Christensen, J.W.; Ahrendt, L.P.; Malmkvist, J.; Nicol, C. Exploratory behaviour towards novel objects is associated with enhanced
      learning in young horses. Sci. Rep. 2021, 14, 1428. [CrossRef]
21.   Bulens, A.; Sterken, H.; Van Beirendonk, S.; Van Thielen, J.; Driessen, B. The use of different objects during a novel object test in
      stabled horses. J. Vet. Behav. 2015, 10, 54–58. [CrossRef]
22.   Hall, C.A.; Cassaday, H.J.; Vincent, C.J.; Derrington, A.M. Cone excitation ratios correlate with color discrimination performance
      in the horse (Equus caballus). J. Comp. Psych. 2006, 120, 438–448. [CrossRef] [PubMed]
23.   McDonnell, S.M. The Equid Ethogram: A Practical Field Guide to Horse Behavior; Eclipse Press: Lexington, KY, USA, 2003; p. 99.
24.   R Core Team. R: A Language Environment for Statistical Computing R Function for Statistical Computing; R Foundation for Statistical
      Computing: Vienna, Austria. Available online: http://www.R-project.org (accessed on 24 March 2021).
25.   Available online: www.tidyverse.org (accessed on 24 March 2021).
26.   Thompson, K.; McGreevy, P.; McManus, P. A Critical Review of Horse-Related Risk: A Research Agenda for Safer Mounts, Riders
      and Equestrian Cultures. Animals 2015, 5, 561–575. [CrossRef] [PubMed]
27.   Lloyd, A.S.; Martin, J.E.; Bornett-Gauci, H.L.I.; Wilkinson, R.G. Horse personality: Variation between breed. Appl. Anim. Behav.
      Sci. 2008, 112, 369–383. [CrossRef]
28.   McGreevy, P.D.; Thomson, P.C. Differences in motor laterality between breeds of performance horses. Appl. Anim. Behav. Sci.
      2006, 99, 183–190. [CrossRef]
29.   Caviello, R.F.; Titto, E.A.L.; Infante, P.; Leme-dos-Santos, T.M.d.C.; Neto, M.C.; Pereira, A.M.F.; Titto, C.G. Proposal and Validation
      of a Scale of Composite Measure Reactivity Score to Characterize the Reactivity in Horses During Handling. J. Eq. Vet. Sci. 2016,
      47, 62–70. [CrossRef]
30.   Marsboll, A.F.; Christensen, J.W. Effects of handling on fear reactions in young Icelandic horses. Equine. Vet. J. 2014, 47, 615–619.
      [CrossRef]
31.   Hartmann, E.; Rehn, T.; Christensen, J.W.; Nielsen, P.P.; McGreevy, P. From the Horse’s Perspective: Investigating Attachment
      Behaviour and the Effect of Training Method on Fear Reactions and Ease of Handing—A Pilot Study. Animals 2021, 11, 457.
      [CrossRef]
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