THE SCIENCE OF DAIRY NUTRITION: THE SNIFFEN LEGACY - USDA
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THE SCIENCE OF DAIRY NUTRITION:
THE SNIFFEN LEGACY
D. R. Mertens
USDA-Agricultural Research Service
US Dairy Forage Research Center
Madison, WI
It is certainly a pleasure to honor Dr. Charles J. (Charlie) Sniffen with this tribute to
his legacy in the field of dairy cattle nutrition. Over the years he and I have celebrated
some highs of intellectual insights and some lows of computer model failures, in
Charlie's vernacular: some real 'horror shows", but in all cases they have been
enjoyable and productive experiences. There is no doubt that he has created a personal
and professional legacy that we would all like to emulate. Personally, Charlie is an
approachable person who can readily engage the attention of both scientists and
producers. His cheerfulness and sense of humor always makes time spent with him
enjoyable, and his enthusiasm is contagious. You could not be associated with Charlie
and not be stimulated by his enthusiasm and support. Professionally, Charlie's ability to
sense the importance of a concept, and envision its application, always provided that
spark needed to encourage himself, and those around him, to tackle complex problems
and obtain solutions that were scientific accomplishments with practical applications.
We are fortunate indeed that Charlie devoted his professional career to research and
extension in dairy nutrition.
ONE OF AGRICULTURE'S MOST HIGHLY CITED SCIENTISTS
Charlie's recognition as one of agriculture's "Most Highly Cited" scientists by the
Institute of Scientific Information (lSl) in Philadelphia attests to the impact that his
research has had on dairy nutrition. According to ISI, 'C.J. Sniffen' was cited more than
2,760 times between 1982 and 2003, and his 22 most-cited papers were referenced
2,130 times during this period. Although the lSl citation tracking does not include
Charlie's early work on protein solubility, which was extensively cited at the time,
examination of Charlie's 22 most-cited papers since 1983 indicates several aspects of
his legacy to dairy cattle nutrition (Table 1). It is clear that he did not work in isolation,
but collaborated with numerous colleagues, graduate students and technical staff to
make discoveries, generate new concepts, develop models, and refine established
ideas. When we think of Charlie's contribution to dairy nutrition, what immediately
comes to mind is his research on protein characterization (Wohlt et al., 1973, 1976;
Crooker et al. 1978; Crawford et al., 1978; Sniffen, 1974, 1980; Sniffen and Hoover,
1978; Sniffen et al., 1979; Krishnamoorthy, et al., 1982, 1983; Muscato et al., 1983;
Licitra, 1999) and the net carbohydrate-protein system (Fox et al., 1988; Fox et al.,
1990; O'Connor et al., 1990; Russell et al., 1992; Sniffen et al., 1992; Fox et al., 1992;
O'Connor et al., 1993).
31
Throughout his career, Charlie maintained a broad range of research activities
related to protein utilization by dairy cows. His PhD dissertation research involved net
amino acid absorption from animals fed alfalfa hay diets (Sniffen and Jacobson, 1975)
and he continued to study the amino acid composition of feed fractions (Macgregor et
al., 1978; Sniffen and Hoover, 1978) and amino acid supplementation of dairy cows
(Papas et al., 1984b; Rogers et al., 1987; Xu et al., 1998; Robinson et al., 2000) for over
25 years. Microbial degradation in the rumen can be a major loss of feed protein and
Charlie collaborated with Dr. J.B. Russell, and others, to investigate protein degradation
and peptide production (Russell et al., 1983; Chen et al., 1987a, b, c). In addition, he
studied effects of degradable and undegradable protein intake by dairy cows on their
reproductive performance (Canfield et al., 1990), milk urea nitrogen levels (Roseler et
al., 1993), and milk production (Van Saun, 1993). Because rumen microbial protein is a
major source of amino acids for dairy cows, Charlie studied factors that affect microbial
protein yield (Stern et al., 1978; Sniffen et al., 1983; Robinson and Sniffen, 1985;
Robinson et al., 1985; Sniffen and Robinson, 1987) and microbial growth factors
(Russell and Sniffen, 1984; Papas et al., 1984). Much of this work contributed in some
way to the development and refinement of the net carbohydrate-protein system (NPCS).
Table 1. The 22 most cited papers that were authored or co-authored by C.J. Sniffen as
recorded by ISI (from 1982 to August 2003— adjusted for incorrect citations).
Citations Authors Reference Topic
307 SNIFFEN, O'Connor, Van Soest, Fox and Sniffen, et al., 1992 NCPS
Russell
231 Russell, O'Connor, Fox, Van Soest and Russell, et al., 1992 NCPS
SNIFFEN
164 Krishnamoorthy, Muscato, SNIFFEN and Krishnamoorthy, et al., 1982 N fractions
Van Soest
144 Curtis, Erb, SNIFFEN, Smith and Kronfeld Curtis, et al., 1985 Transition cow
136 Fox, SNIFFEN, O'Connor, Russell and Van Fox, et al., 1992 NCPS
Soest
114 Russell, SNIFFEN and Van Soest Russell, et al., 1983 Microbial N
112 Krishnarnoorthy, SNIFFEN, Stern and Van Krishnamoorthy, et al., 1983 N fractions
Soest
77 Roseler, Ferguson, SNIFFEN and Herrema Roseler, at al., 1993 Degradability
74 Canfield, SNIFFEN and Butler Canfield,et al., 1990 Degradability
73 O'Connor, SNIFFEN, Fox and Chalupa O'Connor, et al., 1993 NCPS
71 Chen, Strobel, Russell and SNIFFEN Chen, et al., 1987 Microbial N
70 Chen, Russell and SNIFFEN Chen, et al., 1987 AA/peptides
69 Curtis, Erb, SNIFFEN, Smith and Powers Curtis, et al., 1983 Transition cow
68 SNIFFEN and Robinson Sniffen and Robinson, 1987 Microbial N
65 Chen, SNIFFEN and Russell Chen, et al., 1987 AA/peptides
60 Russell and SNIFFEN Russell and Sniffen, 1984 lso-VFA
54 Papas, SNIFFEN and Muscato Papas, et al., 1984 AA/peptides
52 Robinson and SNIFFEN Robinson and Sniffen, 1985 Intake/frequency
48 Rogers, Krishnamoorthy and SNIFFEN Rogers, et al., 1987 AA/peptides
48 Gearhart, Curtis, Erb, Smith, SNIFFEN, Gearhart, et al., 1990 Transition cow
Chase and Cooper
47 Robinson, SNIFFEN and Van Soest Robinson, et al., 1985 Intake/frequency
46 Fox, SNIFFEN and O'Connor Fox, et al., 1988 NCPS
1 32
Although most of the research for which Charlie is best known relates to protein
nutrition in some way, three of Charlie's most highly cited papers investigated
interactions among diseases (Curtis, 1983, 1985) and body condition (Gearhart et al.,
1990) that affect the health and productivity of transition cows.
EARLY SIGNS OF THINGS TO COME
I believe that my first contact with Charlie was in March 1980 at the Distillers' Feed
Conference in Cincinnati, where we both made presentations (Mertens, 1980; Sniffen,
1980). Little did I know that we would become close friends and collaborators on
modeling activities that would continue for more than a decade. At that conference,
Charlie gave a presentation on the "Dynamics of protein solubility and degradability in
ruminant rations" (Sniffen, 1980). In it, Charlie remarked that". . . any protein system, if
it is to be successfully used in the field, needs to recognize the variability in soluble and
bound protein in feedstuffs .....and, "If one recognizes that proteins degrade at various
rates, and accepts the dynamics of rumen function, then one must seriously consider
combining rates of degradability with rumen turnover." He also indicated the range of his
future research endeavors when he indicated that "... 1) time of feeding, 2) feeding
behavior, 3) order of feeding grains and forages, 4) coarseness of material, 5) specific
gravity (with relation to rumen fluid) and, 6) level of feed intake, are all important in
realizing optimum utilization of protein in the ruminant." Finally, he concluded "It is clear
that using solubility alone is too simplistic. . . we need to have a reliable estimate of
degradable protein. . . . we can then take advantage of these dynamics through feeding
strategies and through feed processing . . . much work still needs to be done to quantify
these various factors and how they interact." In this paper, over two decades ago, he
discussed the two topics that would become his legacy to dairy cattle nutrition:
improving the protein nutrition of dairy cows by understanding the complexity and
specificity of protein fractions, and using models to integrate the dynamic processes of
digestion.
SNIFFEN'S PROTEIN NUTRITION LEGACY
In retrospect, Charlie's legacy to dairy cattle nutrition began with his early research
on methods to measure protein solubility. Charlie realized that measurement is the key
to both investigation and utility. Without some ability to determine differences in protein
beyond total crude protein (CP), there was no way to improve our understanding of the
differences in CP that affected ruminant performance, or to develop ration formulation
Systems that would optimize protein utilization. Wohlt et al. (1973) systematically
measured the protein solubility of common feedstuffs and Crooker et al. (1978)
documented that the specific solvent affected the protein solubility measurement.
Crawford et al. (1978) attempted to relate protein solubility to its degradation in the
lumen and Macgregor et al. (1978) related solubility to amino acid profiles. Finally, the
work of Krishnamoorthy et al. (1982, 1983) and Muscato et al. (1983) established the
current system of partitioning protein for the NCPS, which is based on solubility in
borate buffer and in acid and neutral detergent solutions.
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The role of protein solubility in development of better systems to evaluate, and feed,
protein to dairy cows has a mutable and clouded history. The lack of uniformity among
protein solvents was misinterpreted to indicate that protein solubility measurements
were useless. This conclusion inhibited progress in protein utilization research for nearly
20 years, during which time no suitable system was adopted to supplement CP as a
routine laboratory measurement of protein value. During this period, several systems
for improving protein nutrition were developed (see Table 1 in NRC, 1985) that were
based on tabular estimates of protein degradability or undegradability. Likewise, the
NRC systems (1985, 1989) were based on undegradable protein values that wuld not
be determined routinely on specific feeds. Thus, optimizing protein nutrition was
constrained by systems that depended on average tabular values of undegradability,
because no suitable analytical system was available to assess or estimate the protein
degradability of the feed actually being fed. Ideally, we would like to routinely estimate
the extent or rate of degradation of protein in the ruminal environment, but that has
proven unattainable, as yet.
Although protein solubility does not equal protein degradability, this does not mean
that solubility is not a useful measurement that can be related to degradability for
practical use. Much progress in applied protein nutrition was lost because protein
solubility measurements were distained in the pursuit of an unattainable perfect system
for routinely measuring the protein degradability of feeds. Even the most recent NRC
(2001) protein system for dairy cows is based on a rumen in situ nylon bag method that
cannot be routinely used to measure protein degradability, and has numerous
interpretive limitations. Until a practical method is developed that can routinely be used
to estimate degradability more accurately than using tabular values, systems based on
protein degradability are limited by their inability to take advantage of differences among
and within feedstuffs that occur in the field. Charlie's early work helped to identify the
problems in using solubility to measure protein differences, and it set the boundaries for
acceptable measurement and interpretation.
Currently, the NCPS is most complex system available for protein nutrition. It is
based on partitioning protein based on solubility measurements that can be measured
routinely, and using tabular values for rates of degradation. Much of this is the result of
Charlie's input. Although there may be confusion about measuring neutral detergent
(ND) fiber (NDF), or ND insoluble nitrogen, with or without the use of sodium sulfite, this
routine chemical analysis is used to evaluate feeds for use in the NCPS. Based on the
observations of Hintz et al. (1996), it appears that sodium sulfite should be used to
determine NDF routinely, and thereby minimize the protein contamination of NDF for
feeds that are heated. This is the basis for the AOAC Official Method (Mertens, 2002)
for amylase-treated NDF (aNDF). However to partition protein using neutral detergent,
sulfite should not be used because it solubilizes some of the slowly degrading proteins
that affect protein fermentation, especially those produced by heating or cooking feeds.
Throughout his career, Charlie has understood the complexity of protein nutrition in
ruminants and investigated factors affecting microbial growth, protein degradation,
amino acid composition of feed fractions, amino acid supplementation needs of dairy
P 34
I
V
cows, and factors affecting microbial protein flow to the intestines. This interest and
knowledge resulted is his being appointed as a member of the Subcommittee on
Nitrogen Usage in Ruminants of the Committee on Animal Nutrition' that produced the
monograph 'Ruminant Nitrogen Usage" (NRC, 1985; Sniffen, 1986), also known for
many years as the 'green book'. The importance of microbial protein was clearly stated
in the opening sentence of the abstract of the review by Sniffen and Robinson (1987)
as: 'The accuracy of prediction of microbial growth in the rumen and flow of microbial
protein to the intestine is important in predicting protein and carbohydrate utilization in
dairy cattle, as well as the development of a protein and carbohydrate feeding system
that will be an improvement over present systems."
Charlie's legacy to dairy protein nutrition is the recognition that analytical systems for
protein partitioning are the key to estimating ruminal protein degradability and that
estimates of microbial flow to the intestines are crucial in formulating optimum diets for
dairy cows.
SNIFFEN'S RUMEN MODELING LEGACY
I feel more comfortable discussing Charlie's legacy in nutritional modeling than
protein nutrition because it is the area in which I had many direct interactions with him,
and an area in which I have had first-hand experience. Thus, I will approach Charlie's
legacy to rumen modeling from a more personal perspective. In the fall of 1980, I came
back to Cornell University on a sabbatical with the intent of devoting full time to
computer modeling in order to determine the role of modeling in my future research
dairy research. I had been working with Dr. Lane Ely on a ruminant digestion model
(Mertens and Ely, 1979) and we needed to decide if it should be expanded to a more
detailed rumen model, or to a whole animal model. I came to Cornell to work with Dr. T.
Oltenacu and spent the first several months analyzing the extensive northeast DHI
database of lactation data to develop lactation curves as driving functions for a whole
cow model. After completing that effort, I began to work on a detailed rumen model. I
programmed the model in Advanced Continuous Simulation Language (ACSL) that
Lane Ely had been using at the University of Georgia, and started with the dynamic
model that he and I had developed.
Work on the detailed rumen model began in the winter of 1980. My intent was to
develop an all-inclusive model that expressed all known relationships as first- and
second-order mass action equations. After the model was developed, simulations were
planned to detect relationships that had insignificant impacts, and eliminate them, in
order to arrive at an acceptable rumen submodel that could be used in the planned
whole animal model. This approach is the opposite of classical modeling endeavors,
which suggest that you start simply and add complexity as needed to meet modeling
objectives. My objective was to include everything that I knew about the rumen which, in
hindsight, was not a sound modeling objective, but it did provide a tremendous learning
experience for Charlie and me. After I presented some of the concepts that would be
included in the model, and what it might help us understand about feed utilization, at a
NY-PA Dairyman's Seminar (Mertens, 1981), Charlie became my most enthusiastic
35
supporter and the most energetic participant in development of the rumen model.
Typically we would spend at least one day a week going over progress of the model and
its output, and then plan model changes and additions for the next week. This was one
of the most enjoyable, enlightening and productive research activities of my career.
Charlie's support and encouragement was instrumental to its success.
The detailed rumen model grew in complexity until it contained more than 800 input
variables and over 1600 equations. At this point, the rumen model had many
characteristics that would later be included in the NCPS. There were five fractions of
carbohydrates and proteins, the concept of nonfiber carbohydrates calculated by
difference was developed to insure that all feed inputs summed to 100% of dry matter,
starch and pectin were in a combined pool because they were assumed to have similar
rates of digestion, there three different particle fractions, each with its own rate of
rumination and passage, and ruminal microorganisms were grouped into one protozoal
and three bacterial pools.
The addition of the protozoal pool became the crushing blow to the detailed rumen
model. When equations were added to incorporate protozoa, the model began to
behave erratically and generate unpredictable results. My last few months of sabbatical
were spent completely rewriting the computer code in the hopes of discovering a
mistake that could explain the model's results. Following my sabbatical, Charlie, Jim
O'Connor and I would exchange visits for 1 to 2 weeks every 6 months to continue the
modeling effort. Upon my leaving the University of Georgia in 1984, our collaborative
efforts were greatly diminished until Charlie joined Dr. Al Rotz and me with the USDA-
Agricultural Research Service at Michigan State University, to work on the animal
submodel of the Dairy Forage Systems Model (DAFOSYM). Although some aspects of
the detailed rumen model were published in abstracts (Allen et al., 1981; Fadel et al.,
1981, Mertens and Sniffen, 1983), the full model was never published because we
could never explain the model's behavior. Recent discoveries in chaos theory suggest
that we may have encountered one of the first examples of chaotic behavior in a
biological model. In complex nonlinear systems, seemingly small changes in state
variables or input can lead to apparently random and erratic output. I know that both
Charlie and I are disappointed that this model was never useable or published, but we
both gained experience and insights from our development of the detailed rumen model
that have benefited us in other ways.
Although I was not directly involved with development of the NCPS, my experience
working with Charlie on the dynamic ruminal model, from 1981 to 1984, leads me to
believe he was a major force in insuring that the nutrient digestion section of the NCPS
was developed. I suspect that without Charlie's appreciation of the practical application
of kinetic models of digestion; his ability to work with colleagues, graduate students and
computer programmers; his dogged determination to have digestion models used in the
field; and his willingness to develop the feed information library, we would not have the
NCPS as it exits today. It is not surprising that his description of carbohydrate and
protein availability in the NCPS is his most-cited paper. Charlie has maintained an
active interest in evolving the NCPS concept, and he and Bill Chalupa are probably the
36
most intensive users of the current CPM version of the system. They have collaborated
extensively to use, evaluate and refine the concept (Sniffen et al., 1989; Chalupa and
Sniffen, 1994).
It is fitting that his efforts in creating the NCPS should be the second legacy that
Charlie contributed to dairy nutrition.
CONCLUSIONS
Charlie's legacy to dairy protein nutrition is the improved description of protein
fractions, that allow dairy cattle nutritionists to formulate rations more accurately, and
the integration of this information into a kinetic model (NCPS) that allows interactions of
these protein fractions with microbial growth and fermentation in the rumen. His legacy
in modeling is the development of a complex analytical and kinetic database of feed
information that is used in the NCPS, and will undoubtedly serve as a reference for
future modeling efforts.
Thus, it seems appropriate to describe Charlie's legacy to dairy nutrition in the words
"complexity" and "integration", and the science of dairy cattle nutrition will forever be in
his debt for the "integrated complexity" of his contributions.
REFERENCES
Allen, M. S., D. R. Mertens and C. J. Sniffen. 1981. A mathematical model of lag phase
during ruminal fermentation. J. Anim. Sci. 53(Suppl.1): 455.
Canfield, R. W., C. J. Sniffen and W. R. Butler. 1990. Effects of excess degradable
protein on postpartum reproduction and energy balance in dairy cattle. J. Dairy
Sci. 73: 2342-2349.
Chalupa, W., and C. J. Sniffen. 1994. Carbohydrate, protein and amino acid nutrition of
lactating dairy cattle. Recent Adv. Anim. Nutr. Nottingham University Press. p.
265-275.
Chen, G., J. B. Russell and C. J. Sniffen. 1987a. A procedure for measuring peptides in
rumen fluid and evidence that peptide uptake can be a rate-limiting step in
ruminal protein degradation. J. Dairy Sci. 70: 1211-1219.
Chen, G., C. J. Sniffen and J. B. Russell. 1987b. Concentration and estimated flow of
peptides from the rumen of dairy cattle: effects of protein quantity, protein
solubility, and feeding frequency. J. Dairy Sci. 70: 983-992.
Chen, G., H. J. Strobel, J. B. Russell and C. J. Sniffen. 1987c. Effect of hydrophobicity
on utilization of peptides by ruminal bacteria in vitro. AppI. Environ. Microbiol. 53:
2021-2025.
Crawford, R. J. Jr., W. H. Hoover, C. J. Sniffen and B. A. Crooker. 1978. Degradation of
feedstuff nitrogen in the rumen versus nitrogen solubility in three solvents. J.
Anim. Sci. 46:1768-1775.
Crooker, B. A., C. J. Sniffen, W. H. Hoover and L. L. Johnson. 1978. Solvents for
soluble nitrogen measurements in feedstuffs. J. Dairy Sci. 61: 437447.
37
Curtis, C. R., H. N. Erb, C. J. Sniffen, R. D. Smith and D. S. Kronfeld. 1985. Path
analysis of dry period nutrition, postpartum metabolic and reproductive disorders,
and mastitis in Holstein cows. J. Dairy Sci. 68: 2347-2360.
I
Curtis, C. R., H. N. Erb, C. J. Sniffen, R. D. Smith and P. A. Powers. 1983. Association
of parturient hypocalcemia with eight periparturient disorders in Holstein cows. J.
Am. Vet. Med. Assoc. 183: 559-561.
Fadel, J.G., P. J. Van Soest and D. R. Mertens. 1981. Fiber digestion kinetics in the
rumen. J. Anim. Sci. 53(Suppl.1): 274.
Fox, D. G., C. J. Sniffen and J. D. O'Connor. 1988. Adjusting nutrient requirements of
beef cattle for animal and environmental variations. J. Anim. Sci. 66: 1475-1495.
Fox, D. G., C. J. Sniffen, J. D. O'Connor, J. B. Russell and P. J. Van Soest. 1992. A net
carbohydrate and protein system for evaluating cattle diets. Ill. Cattle
requirements and diet adequacy. J. Anim. Sci. 70: 3578-3596.
Fox, D. G., C. J. Sniffen, J. D. O'Connor, J. B. Russell and P. J. Van Soest. 1990. The
Cornell net carbohydrate and protein system for evaluating cattle diets. I. A
model for predicting cattle requirements and feedstuff utilization. Search Agric.
Cornell Univ. Agric. Exp. Stn. 34: 7-83.
Gearhart, M. A., C. R. Curtis, H. N. Erb, R. D. Smith, C. J. Sniffen, L. E. Chase and M.
D. Cooper. 1990. Relationship of changes in condition score to cow health in
Holsteins. J. Dairy Sci. 73: 3132-3140.
Hintz, R. W., Mertens, D. R. and Albrecht, K. A. 1996. Effects of sodium sulfite on
recovery and composition of detergent fiber and lignin. J. AOAC. Inter. 79: 16-22.
Krishnamoorthy, U., C. J. Sniffen, M. D. Stern and P. J. Van Soest. 1983. Evaluation of
a mathematical model of rumen digestion and an in vitro simulation of rumen
proteolysis to estimate the rumen-undegraded nitrogen content of feedstuffs. Br.
J. Nutr. 50: 555-568.
Krishnamoorthy, U., T. V. Muscato, C. J. Sniffen and P. J. Van Soest. 1982. Nitrogen
fractions in selected feedstuffs. J. Dairy Sci. 65: 217-225.
Licitra, G., P. J. Van Soest, I. Schadt, S. Carpino and C.J. Sniffen.1999. Influence of
the concentration of the protease from Streptomyces griseus relative to ruminal
protein degradability. Anim. Feed Sci. Technol. 77: 99-113.
Macgregor, C. A., C. J. Sniffen and W. H. Hoover. 1978. Amino acid profiles of total and
soluble protein in feedstuffs commonly fed to ruminants. J. Dairy Sci. 61:566-573.
Mertens, D. R. 1980. Fiber content and nutritional density in dairy rations. Proc.
Distiller's Feed Conf. 35: 3543.
Mertens, D. R. 1981. Utilization of farm produced feeds by the cow. New York -
Pennsylvania Dairyman's Seminar, Coop. Ext. of Cornell and Pennsylvania State
Univ., Feb. 24-26, Owego, NY. 16 pp.
Mertens, D. R. 2002. Gravimetric determination of amylase-treated neutral detergent
fiber in feeds using refluxing in beakers or crucibles: collaborative study. J.
AOAC Inter. 85:1217-1240.
Mertens, D. R. and L. 0. Ely. 1979. A dynamic model of fiber digestion and passage in
the ruminant for evaluating forage quality. J. Anim. Sci. 49: 1085-1095.
Mertens, D. R. and C. J. Sniffen. 1983. Developing a dynamic model of the lactating
cow. J. Anim. Sci. 57(Suppl.1): 71.
38
Muscato, T. V., C. J. Sniffen, U. Krishnamoorthy and P.J. Van Soest. Amino acid
content of noncell and cell wall fractions in feedstuffs. J. Dairy Sci. 66: 2198-
2207.
NRC (National Research Council). 1985. Ruminant Nitrogen Usage. National Academy
Press, Washington, DC. 138 pp.
NRC (National Research Council). 1989. Nutrient Requirements of Dairy Cattle.
revised ed. National Academy Press, Washington, DC. 157 pp.
NRC (National Research Council). 2001. Nutrient Requirements of Dairy Cattle. 1"
revised ed. National Academy Press, Washington, DC. 381 pp.
O'Connor, J. D., C. J. Sniffen and D.G. Fox. 1990. The Cornell net carbohydrate and
protein system for evaluating cattle diets. II. A computer spreadsheet for diet
evaluation. Search Agric. Cornell Univ. Agric. Exp. Stn. 34: 84-128.
O'Connor, J. D., C. J. Sniffen, D. G. Fox and W. Chalupa. 1993. A net carbohydrate and
protein system for evaluating cattle diets. IV. Predicting amino acid adequacy. J.
Anim. Sci. 71(5): 1298-1311.
Papas, A. M., S. R. Ames, R. M. Cook, C. J. Sniffen and C. E. Polan.1984a. Production
responses of dairy cows fed diets supplemented with ammonium salts of iso C-4
and C-5 acids. J. Dairy Sci. 67: 276-293.
Papas, A. M., C. J. Sniffen and T. V. Muscato. 1984b. Effectiveness of rLrnen-protected
methionine for delivering methionine postruminally in dairy cows. J. Dairy Sci. 67:
545-552.
Robinson, P. H., C. J. Sniffen and P. J. Van Soest. 1985. Influence of level of feed
intake on digestion and bacterial yield in the forestomachs of dairy cattle. Can. J.
Anim. Sci. 65:437-444.
Robinson, P.H., W. Chalupa, C. J. Sniffen, W. E. Julien, H. Sato, T. Fujieda,T. Ueda,
and H. Suzuki. 2000. Influence of abomasal infusion of high levels of lysine or
methionine, or both, on ruminal fementation, eating behavior, and performance of
lactating dairy cows. J.Anim. Sci. 78: 1067-1077.
Robinson, P. H. and C. J. Sniffen. 1985. Forestomach and whole tract digestibility for
lactating dairy cows as influenced by feeding frequency. J. Dairy Sci. 68: 857-
867.
Rogers, J. A., U. Krishnamoorthy and C. J. Sniffen. 1987. Plasma amino acids and milk
protein production by cows fed rumen-protected methionine and lysine. J. Dairy
Sci. 70: 789-798.
Roseler, D. K., J. D. Ferguson, C. J. Sniffen and J. Herrema. 1993. Dietary protein
degradability effects on plasma and milk urea nitrogen and milk nonprotein
nitrogen in Holstein cows. J. Dairy Sci. 76: 525-534.
Russell, J. B., J. D. O'Connor, D. G. Fox, P. J. Van Soest and C. J. Sniffen. 1992. A net
carbohydrate and protein system for evaluating cattle diets. I. Ruminal
fermentation. J. Anim. Sci. 70: 3551-3561.
Russell, J. B. and C. J. Sniffen. 1984. Effect of carbon-4 and carbon-5 volatile fatty
acids on growth of mixed rumen bacteria in vitro. J. Dairy Sci. 67: 987-994.
Russell, J. B., C. J. Sniffen and P. J. Van Soest. 1983. Effect of carbohydrate limitation
on degradation and utilization of casein by mixed rumen bacteria. J. Dairy Sci.
66: 763-775.
39Sniffen, C. J. 1974. Nitrogen utilization as related to solubility of NPN and protein in
feeds. Proc. Cornell Nutr. Conf., p. 12-18.
Sniffen, C.J. and W. H. Hoover.1978. Amino acid profile of dietary bypass protein and
its importance to ruminants. Proc. Distiller's Feed Conf. 33: 61-69.
Sniffen, C.J. 1980. Dynamics of protein solubility and degradability in ruminant rations.
Proc. Distiller's Feed Conf. 35: 69-75.
Sniffen, C.J. 1986. Dynamic aspects of protein utilization in ruminants (review of NRC
report). Proc. Cornell Nutr. Conf. p. 1-9.
Sniffen, C.J., W. Chalupa and J. Ferguson. 1989. The impact of controlling protein,
amino acid and carbohydrate fractions on productivity and body weight change in
BST herds. Monsanto Technical Symposium. Monsanto Agricultural Co., Animal
Sciences Division, St. Loius. p. 27-33.
Sniffen, C.J., W. H. Hoover, L. L. Junkins, B. A. Crooker, and C. A. Macgregor. 1979.
Variation in protein and soluble carbohydrate composition of various feedstuffs.
Proc Cornell Nutr. Conf. p. 119-125.
Sniffen, C. J. and D. R. Jacobson. 1975. Net amino acid absorption in steers fed alfalfa
hay cut a two stages of maturity. J. Dairy. Sci. 58: 371-385.
Sniffen, C. J., J. D. O'Connor, P. J. Van Soest, D. G. Fox and J. B. Russell. 1992. A net
carbohydrate and protein system for evaluating cattle diets. II. Carbohydrate and
protein availability. J. Anim. Sd. 70: 3562-3577.
Sniffen, C. J. and P. H. Robinson. 1987. Microbial growth and flow as influenced by
dietary manipulations. J. Dairy Sci. 70: 425-441.
Sniffen, C. J., J. B. Russell and P. J. Van Soest.1983. The influence of carbon source,
nitrogen source and growth factors on rumen microbial growth. Proc. Cornell
Nutr. Conf., p. 26-33.
Stern, M. D., W. H. Hoover, C. J. Sniffen, B. A. Crooker and P. H. Knowlton. 1978.
Effects of nonstructural carbohydrate, urea and soluble protein levels on
microbial protein synthesis in continuous cultures of rumen contents. J. Anim.
Sci. 47: 944-956.
Van Saun, R.J., S.C. Idleman and C. J. Sniffen.1993. Effect of undegradable protein
amount fed prepartum on postpartum production in first lactation Holstein cows.J.
Dairy Sci. 76: 236-244.
Wohlt, J. E., C. J. Sniffen and W. H. Hoover. 1973. Measurement of protein solubility in
common feedstuffs. J. Dairy Sci. 56: 1052-1057.
Wohit, J. E., C. J. Sniffen, W. H. Hoover, L. L. Johnson and C. K. Walker. 1976.
Nitrogen metabolism in wethers as affected by dietary protein solubility and
amino acid profile. J. Anim. Sci. 42:1280-1289.
Xu, S., J. H. Harrison, W. Chalupa, C. J. Sniffen, H. Sato, T Fujieda, K. Watanabe, T.
Ueda and H. Suzuki. 1998. The effect of ruminal bypass lysine and methionine
on milk yield and composition of lactating cows. J. Dairy Sci. 81: 1062-1077.
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