Development, selection criteria, and performance of Composite IV sheep at
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Development, selection criteria, and performance of Composite IV sheep at the
U.S. Meat Animal Research Center1,2
Thomas W. Murphy,3 Brad A. Freking , Gary L. Bennett, and John W. Keele
USDA, ARS, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933
Published by Oxford University Press on behalf of the American Society of Animal Science 2020.
Downloaded from https://academic.oup.com/tas/article/4/Supplement_1/S150/6043884 by guest on 24 December 2020
This work is written by (a) US Government employee(s) and is in the public domain in the US.
This Open Access article contains public sector information licensed under the Open Government
Licence v2.0 (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/).
Transl. Anim. Sci. 2020.4:S150–S154
doi: 10.1093/tas/txaa125
INTRODUCTION work was to provide a discussion of the devel-
opment, selection criteria, and performance of
Ewe reproduction and lamb survival affect eco- Composite IV ewes and lambs.
nomic and biological efficiency more than other
production traits (Wang and Dickerson, 1991;
Borg et al., 2007). Crossing super-prolific (e.g., MATERIALS AND METHODS
Finnsheep and Romanov) and domestic breeds
has greatly enhanced ewe reproductive perform- Composite IV Development
ance in shed-lambing systems (Thomas, 2010). Matings that contributed to the develop-
However, most lambs in Intermountain West and ment of the Composite IV are displayed in
Great Plains states are born on open range (28%) Table 1. An earlier experiment conducted at the
or fenced pasture (31%; USDA APHIS, 2014) and U.S. Meat Animal Research Center (USMARC;
reports of ewe productivity and lamb survival Clay Center, NE) generated F1 lambs that were
from these prolific breed types in extensive sys- born to Romanov dams and sired by wool or
tems are scarce. Eliminating the cost of shearing hair breed rams. Unpublished results indicated
may also be advantageous in environments that that total weight of lamb weaned was greatest for
do not favor the production of high-quality wool. White Dorper × Romanov (WD-R) ewes in both
The Composite IV is a ½ Romanov, ¼ Katahdin, shed- and pasture-lambing systems. Katahdin
¼ White Dorper hair sheep developed at the U.S. × Romanov (K-R) ewe productivity was numer-
Meat Animal Research Center and has since been ically lower than most other F1, but unquanti-
managed and selected in a forage-based system fied Katahdin attributes such as coat shedding,
with limited human intervention from lambing enhanced internal parasite tolerance, and foot
through weaning. The objective of the present soundness are favorable for low-input, for-
age-based systems.
Twenty-two registered Katahdin and 19 White
1
USDA is an equal opportunity provider and employer. Dorper rams were sourced from industry flocks
The mention of trade names of commercial products in this and bred to 226 USMARC Romanov ewes to ini-
article is solely for the purpose of providing specific informa- tiate the Composite IV. Some WD-R and K-R
tion and does not imply recommendation or endorsement by
ewes were retained from the initial experiment,
the USDA.
but most were re-generated over the next few
2
The authors acknowledge Kreg A. Leymaster (retired)
who provided the primary leadership for conceiving and
years. Initial crosses focused on developing a pas-
designing this composite and USMARC sheep operations ture lambing, WD-R composite flock. These F2
staff for the care and management of animals. WD-R and F1 WD-R were reciprocally mated to
3
Corresponding author: tom.murphy@usda.gov F1 K-R to produce first-cross Composite IV lambs.
Received May 1, 2020. Inter-se matings between first-cross Composite
Accepted July 8, 2020. IV ewes and rams produced the final cross (i.e.,
S150Breeding for low-input lambing systems S151
Table 1. Contributing breeds, their crosses, and cor- Lamb and Ewe Traits
responding lamb birth year of the Composite IV
Lamb traits included survival from birth to
Breed composition1
weaning (n = 7,851) and body weight (BW) at
Sire (n) Dam (n) Lamb Birth year weaning (BWW; n = 5,995). For the purposes of this
WD (19) WD-R 2001 to 2004, 2007, 2011
R (226) study, 130 nursery-reared lambs were considered a
K (22) K-R 2001 to 2003, 2008, 2011
preweaning mortality. Ewe BW was recorded prior
WD-R WD-R WD-R 2005 to 2008
WD-R K-R 2008 to 2012
to mating (BWM) each year, and fertility was calcu-
K-R WD-R
C-IV1
2009 to 2012
lated as whether a ewe present at mating lambed the
C-IV1 C-IV1 C-IV2 2010 to 2018 following spring (n = 3,153). Number of lambs ac-
counted for near parturition (NLB; n = 2,801) was
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1
K = Katahdin; WD = White Dorper; R = Romanov; C-IV1 = first- calculated on a per ewe lambing basis and included
cross Composite IV; C-IV2 = second-cross Composite IV.
all live and dead lambs for which parentage could
be determined. Number of lambs weaned (NLW) or
second-cross Composite IV) born in 2010, and this total litter weaning weight (LWW) per ewe lambing
flock has since remained closed while maintaining did not include lambs that died or were transferred
the genetic diversity of foundational sires. to the nursery.
Flock Management and Selection Criteria Analyses
The Composite IV mating season commenced Only records from second-cross Composite IV
each year in mid-December for 35 d. Ewes were ex- lambs and ewes were considered in the following
posed to rams in single-sire mating pens from the analyses. Birth date and birth BW of most lambs
2010 to 2015 mating seasons and have since been were unknown, so could not be used to adjust
group mated with 3 or 4 rams (approximately 20 lamb or ewe traits. Lamb traits were analyzed with
ewes per ram). Ewes were fed a corn-silage based fixed effects of birth type (1, 2, or 3+), sex (ewe or
ration while in mating but were managed on pas- ram), dam age (1 to 5 yr), and birth year (2010 to
ture at all other times of the year. Mature ewes 2018) and the random effect of sire. Ewe traits were
were managed on stockpiled forage throughout analyzed as repeated measures with fixed effects
the winter and supplemented alfalfa hay and whole of ewe age (1 to 5 yr) and ewe birth year (2010 to
shelled corn. Approximately 3 wk before expected 2017). Additionally, a random effect of sire was fit
parturition, groups of ~75 ewes were assigned to 4 and a compound symmetric covariance structure
ha lambing paddocks. with heterogenous variance across age was assumed
From 2010 to 2016, lambs were tagged near for the ewe effect. To assess the impact of litter size
birth, but periparturient ewes and lambs have since at birth (1, 2, or 3) on mature ewe (2 to 5 yr) prod-
been undisturbed and lambs are not given unique uctivity at weaning, NLW and LWW (n = 1,769)
identification until they die, enter the nursery, or are were also analyzed in similar models above with the
weaned. Dam assignment was through observation additional fixed effect of NLB. Lamb survival and
(2010 only) or DNA (2011 to present). Lambs were ewe fertility were analyzed as binary variables in the
weaned and weighed at approximately 10 wk then GLIMIIX procedure of SAS (v. 9.4; SAS Institute
entered the drylot for finishing or until selection de- Inc., Cary, NC), and all other traits were analyzed
cisions were made. in the MIXED procedure. All cross-classified two-
The flock is currently at ~650 ewes with a tar- way interactions were fit and subsequently removed
geted goal of 800 ewes. Independent culling lev- if they were not significant (P < 0.05). Birth year
els are in place for white color, ability to shed, effects and interactions are not discussed.
polled, type of rearing, and genotypes at two loci:
scrapie prion (PRNP) and susceptibility to Ovine
RESULTS
Progressive Pneumonia (TMEM154). Selection of
twin- and triplet-reared rams over singles should
gradually improve lamb survival without the need Lamb Traits
for human intervention. However, as several traits Birth type x sex interaction was significant in
are incorporated into the selection strategy, im- the analysis of lamb survival to weaning (P < 0.01).
provement of individual traits will be relatively Within single and twin born lambs, survival was
slow. similar between ewe and ram lambs (P ≥ 0.53).
Translate basic science to industry innovationS152 Murphy et al.
However, within triplet and larger litters, survival age classes (P ≤ 0.02). Similarly, LWW was least for
was greater for ram than ewe lambs (0.69 ± 0.02 vs. 1-yr-old ewes (P < 0.01), lower for 2-yr-old than
0.61 ± 0.02; P < 0.01). Least-squares means for the 3- or 4-yr-old ewes (P ≤ 0.02), but not different
main effects on lamb traits are displayed in Table 2. between 2- and 5-yr-old ewes (P = 0.21).
As main effects, lamb survival was not influenced The frequency of litter size class at birth and
by sex (P = 0.35) but decreased with increasing weaning and least-squares means for the main ef-
birth type (P < 0.01). Lambs born to 1- and 5-yr-old fect of NLB on NLW and LWW are displayed
dams had lower survival than other ages (P ≤ 0.04). in Table 4. Most mature Composite IV ewes that
Lambs reared by 1-yr-old dams had the lightest gave birth to single or twin lambs reared their en-
BWW (P < 0.01). As expected, BWW was lighter for tire litter through weaning, while most ewes that
ewe than ram lambs (P < 0.01) and decreased with gestated triplets reared twins. The ewe age × NLB
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increasing birth type (P < 0.01). interaction was significant in the analyses of NLW
and LWW (P ≤ 0.03) due to relative differences be-
Ewe Traits tween but not a re-ranking among NLB classes
within ewe age. On average, both NLW and LWW
Least-squares means for the main effect of increased with increasing NLB (P < 0.01).
age on ewe performance are displayed in Table 3.
Ewe BWM increased with age and was different DISCUSSION
between every class (P ≤ 0.02). Fertility of 1-yr-old
ewes was lower than all other ages (P < 0.01). One- Component breeds and selection pressure of
year-old ewes had the fewest lambs born and NLW the Composite IV has resulted in a white, polled,
(P < 0.01), and 2-yr-old ewes had fewer than older maternal composite with predicted 62.5% in-
dividual and maternal heterosis. Composite IV
Table 2. Least-squares means for the main effects sheep do not require docking or shearing and have
of dam age, birth type, and sex on Composite IV been managed in a forage-based, pasture-lambing
lamb traits system which drastically reduces costs of produc-
tion. Input costs were not evaluated in the present
Trait1
study, but Ali et al. (2005) estimated that annual ewe
Effect Level Survival BWW, kg feed costs in a pasture-lambing system in Iowa were
Dam age, yr 1 0.78 ± 0.01b 15.2 ± 0.11c
54% lower than expected from a typical shed-lamb-
2 0.82 ± 0.01a 16.7 ± 0.11b
ing system. Inclement weather, predation, and in-
3 0.84 ± 0.01a 17.4 ± 0.13a
4 0.83 ± 0.01a 17.3 ± 0.15a
ternal parasitism can certainly limit performance in
5 0.78 ± 0.02b 17.3 ± 0.21a,b
range- or pasture-lambing systems and this should
Birth type, n 1 0.90 ± 0.01a 19.9 ± 0.14a be considered jointly when evaluating profitability.
2 0.82 ± 0.01b 15.9 ± 0.09b Burfening and Van Horn (1993) compared the
3+ 0.65 ± 0.01c 14.6 ± 0.18c productivity of Western white-faced ewes under
Sex Ewe 0.80 ± 0.01 16.3 ± 0.10b shed- or range-lambing in Montana. While shed-
Ram 0.81 ± 0.01 17.2 ± 0.10a lambed ewes had greater NLW and LWW per
ewe exposed (0.98 lambs and 39.2 kg) than range-
1
Survival = lamb survival from birth to weaning (0 or 1);
BWW = lamb body weight at weaning (~10 wk of age). lambed ewes (0.88 lambs and 32.1 kg), economic
a–c
Means within a column and effect with no common superscript simulation of these performance levels generally
are different (P ≤ 0.04). estimated greater returns for range-lambed ewes.
Table 3. Least-squares means (± SE) for the main effect of age on Composite IV ewe traits
Trait1
Age, yr BWM, kg Fertility NLB, n NLW, n LWW, kg
1 40.8 ± 0.24e 0.84 ± 0.01b 1.55 ± 0.02c 1.24 ± 0.02c 19.7 ± 0.31c
2 50.7 ± 0.25d 0.93 ± 0.01a 1.99 ± 0.03b 1.57 ± 0.03b 24.3 ± 0.39b
3 57.8 ± 0.31c 0.92 ± 0.01a 2.20 ± 0.03a 1.78 ± 0.03a 27.5 ± 0.53a
4 60.9 ± 0.35b 0.92 ± 0.01a 2.23 ± 0.04a 1.83 ± 0.04a 26.4 ± 0.63a
5 62.2 ± 0.45a 0.92 ± 0.02a 2.23 ± 0.05a 1.75 ± 0.06a 26.3 ± 0.90a,b
1
BWM = ewe body weight at mating; fertility = whether a ewe present at mating lambed the following spring (0 or 1); NLB/NLW = number of
lambs born/weaned per ewe lambing; LWW = total litter weaning weight per ewe lambing.
a–e
Means within a column with no common superscript are different (P ≤ 0.02).
Translate basic science to industry innovationBreeding for low-input lambing systems S153
Table 4. Descriptive statistics for litter size at weaning in relation to number of lambs born (NLB) and
least-squares means (± SE) for the main effect of NLB on number of lambs weaned (NLW) and total litter
weaning weight (LWW) of Composite IV ewes
No. weaned, %
NLB (%)1 0 1 2 3 NLW, n LWW, kg
1 (16.6) 12.6 87.4 — — 0.87 ± 0.05c 16.4 ± 0.74c
2 (58.7) 4.1 24.8 71.1 — 1.70 ± 0.03b 26.0 ± 0.44b
3 (24.7) 5.9 16.0 45.3 32.8 2.06 ± 0.03a 28.9 ± 0.55a
1
Based on a total of 293 single, 1,039 twin, and 437 triplet litters from mature ewes (2 to 5 yr old at lambing).
a–c
Means within a column with no common superscript are different (P < 0.01).
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Performance in extensive rangeland operations has milk replacer and biases phenotypes for selection.
been greatly enhanced by infusing a proportion of Pasture-born lamb survival was greatest for singles
prolific genetics into typical Western white-faced (81% to 99%), intermediate for twins (59% to 77%),
flocks (e.g., Rambouillet and Targhee). Walker et al. and lowest for triplets (41% to 91%) in the study of
(1993) evaluated mature ¾ Targhee × ¼ Finnsheep Ali et al. (2005). Notter et al. (2018) evaluated NLB
ewes in range- or shed-lambing treatments in effects in shed-lambed Polypay and R-WD × R
Idaho (NLB = 1.93 lambs). Litter size at 25 d was ewes and reported that NLW was 0.2 lambs greater
greater for shed- than range-lambed ewes (1.63 vs. for triplet- than twin-bearing ewes. However, tri-
1.42 lambs) but differences were less pronounced plet-bearing ewes also lost an additional 0.75 lambs
by weaning (1.13 vs. 1.08 lambs). However, BWW which corresponded to 3.75 dead lambs per addi-
was lighter for shed- than range-born lambs (30.9 tional lamb weaned. Triplet-bearing Composite
vs. 32.3 kg), so that ewe LWW was similar between IV ewes in the present study weaned 0.36 but lost
treatments. Terminally mated, pasture-lambed 0.64 more lambs than twin-bearing ewes (i.e., 1.78
Polypay × Dorset ewes evaluated in the Midwest dead lambs/lamb weaned). Ewe and lamb supple-
by Ali et al. (2005) had similar NLB (1.65 to 1.74 mentation would likely improve triplet survival and
lambs) and LWW (32.1 to 36.2 kg) to the range- growth through weaning, but results suggest an
lambed ewes above. intermediate optimum for ewe NLB in extensive
Range- and pasture-lambed ewes in previous stud- production systems.
ies had lower NLW but greater LWW than straight- Composite IV breeding stock have been dissem-
bred Composite IV in the present study. Notter et al. inated and is gaining regional popularity though no
(2017) evaluated terminally mated Rambouillet, breed society has been formed. Phenotypic selec-
Polypay, and Romanov-White Dorper × Rambouillet tion of this composite has favored multiple-rearing
(R-WD × R) ewes through four parities in Idaho. ability in a forage-based system with reduced labor
Cumulative NLW and LWW was much greater for inputs. Since lamb survival and ewe prolificacy, ma-
R-WD × R (4.8 lambs and 153 kg) than Polypay (3.8 ternal ability, and longevity are lowly to moderately
lambs and 123 kg) and Rambouillet ewes (2.9 lambs heritable traits, annual response in the present se-
and 99 kg). Therefore, ewe productivity was greatly lection scheme is expected to be low. Composite IV
enhanced with the inclusion of ¼ Romanov breeding lamb BW at weaning is lighter than most maternal
and may be expected to be greater in ½ Romanov or dual-purpose breeds and, if this remains through
ewes. Although no direct comparisons of Composite finishing, may present challenges in meeting carcass
IV ewes have been published, a recently completed expectations of traditional U.S. markets. Direct se-
USMARC experiment evaluated Composite IV, lection for lamb BW and/or use of terminal sires
Katahdin, and Polypay ewes through four parities of could improve lamb survival and growth. Planned
pasture lambing. Preliminary results indicate prod- research in this flock will evaluate terminal sire
uctivity and longevity were greatest for Composite breeds, ewe productivity in shed and pasture
IV ewes especially when mated to Texel rams. lambing, and pedigree-based or genomic-enhanced
Genetic improvement of NLB increases the fre- estimated breeding values for use in selection.
quency of triplet or larger litters which may reduce
lamb survival (Borg et al., 2007). Shed-lambing sys- LITERATURE CITED
tems commonly reduce triplet litters by cross-fos- Ali, A., D. G. Morrical, and M. P. Hoffman. 2005. Evaluating
tering or artificially rearing lambs. While this may Texel-, Suffolk-, and Columbia-sired offspring:
improve survival, it requires additional labor or I. Prolificacy, survival, and pre-weaning growth traits
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under a forage-based lambing system. Prof. Anim. Sci. Thomas, D. L. 2010. Performance and utilization of Northern
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2007. Breeding objectives for Targhee sheep. J. Anim. Sci. doi:10.1017/S1751731110000856
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