A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability.

The Cornell Net Carbohydrate and Protein System (CNCPS) has a submodel that predicts rates of feedstuff degradation in the rumen, the passage of undegraded feed to the lower gut, and the amount of ME and protein that is available to the animal. In the CNCPS, structural carbohydrate (SC) and nonstructural carbohydrate (NSC) are estimated from sequential NDF analyses of the feed. Data from the literature are used to predict fractional rates of SC and NSC degradation. Crude protein is partitioned into five fractions. Fraction A is NPN, which is trichloroacetic (TCA) acid-soluble N. Unavailable or protein bound to cell wall (Fraction C) is derived from acid detergent insoluble nitrogen (ADIP), and slowly degraded true protein (Fraction B3) is neutral detergent insoluble nitrogen (NDIP) minus Fraction C. Rapidly degraded true protein (Fraction B1) is TCA-precipitable protein from the buffer-soluble protein minus NPN. True protein with an intermediate degradation rate (Fraction B2) is the remaining N. Protein degradation rates are estimated by an in vitro procedure that uses Streptomyces griseus protease, and a curve-peeling technique is used to identify rates for each fraction. The amount of carbohydrate or N that is digested in the rumen is determined by the relative rates of degradation and passage. Ruminal passage rates are a function of DMI, particle size, bulk density, and the type of feed that is consumed (e.g., forage vs cereal grain).

[1]  P. V. Soest,et al.  Amino Acid Content of Noncell and Cell Wall Fractions in Feedstuffs , 1983 .

[2]  C. H. Gordon,et al.  Relationships of Forage Compositions With Rates of Cell Wall Digestion and Indigestibility of Cell Walls , 1972 .

[3]  P. V. Soest,et al.  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 , 1983, British Journal of Nutrition.

[4]  D. Fox,et al.  Variation in Protein and Fiber Fractions in Pasture During the Grazing Season , 1988 .

[5]  R. L. Baldwin,et al.  A dynamic model of ruminant digestion for evaluation of factors affecting nutritive value , 1977 .

[6]  Charles J. Sniffen,et al.  Nitrogen fractions in selected feedstuffs , 1982 .

[7]  M. Murphy,et al.  Nutrient digestion in the large intestine as influenced by forage to concentrate ratio and forage physical form. , 1989, Journal of dairy science.

[8]  G. Varga,et al.  Rate and Extent of Neutral Detergent Fiber Degradation of Feedstuffs in Situ , 1983 .

[9]  E. Russek-Cohen,et al.  Simultaneous measures of rates of ruminal digestion and passage of feeds for prediction of ruminal nitrogen and dry matter digestion in lactating dairy cows. , 1987, Journal of animal science.

[10]  D. Fox,et al.  Protein Distribution in Four Cool-Season Grass Varieties Alone or in Combination with Trefoil , 1988 .

[11]  P. V. Soest,et al.  Feed Intake, Apparent Diet Digestibility, and Rate of Particulate Passage in Dairy Cattle , 1982 .

[12]  J. Prescott,et al.  The effect in sheep of physical form and stage of growth on the sites of digestion of a dried grass , 1972, British Journal of Nutrition.

[13]  J. Russell,et al.  Protein and Energy as an Integrated System. Relationship of Ruminal Protein and Carbohydrate Availability to Microbial Synthesis and Milk Production , 1988 .

[14]  M. R. Stokes,et al.  Effect of dietary concentration of total nonstructural carbohydrate on energy and nitrogen metabolism and milk production of dairy cows. , 1983, Journal of dairy science.

[15]  D. Beever,et al.  The effect in sheep of physical form on the sites of digestion of a dried lucerne diet , 1972, British Journal of Nutrition.

[16]  E. L. Cox,et al.  Model of cellulose disappearance from the rumen. , 1972, Journal of dairy science.

[17]  D. Waldo,et al.  Insolubility of Proteins in Ruminant Feeds by Four Methods , 1979 .

[18]  L. O. Ely,et al.  A Dynamic Model of Fiber Digestion and Passage in the Ruminant for Evaluating Forage Quality , 1979 .

[19]  P. V. Soest.  Nutritional Ecology of the Ruminant , 1994 .

[20]  J. Thornley,et al.  Simulation of the metabolism of absorbed energy-yielding nutrients in young sheep , 1984, British Journal of Nutrition.

[21]  M. Roe,et al.  Techniques for measuring protein fractions in feedstuffs , 1990 .

[22]  W. Horwitz.  Official Methods of Analysis , 1980 .

[23]  R. Axford,et al.  The digestibility of amino acids in the small intestine of the sheep , 1981, British Journal of Nutrition.

[24]  P. V. Soest,et al.  Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. , 1991, Journal of dairy science.

[25]  D. Armstrong,et al.  Studies on intestinal digestion in the sheep , 1969, British Journal of Nutrition.

[26]  W. Hoover.  Digestion and absorption in the hindgut of ruminants. , 1978, Journal of animal science.

[27]  H. Goering,et al.  Forage fiber analyses (apparatus, reagents, prcedures, and some applications) , 1970 .

[28]  L. Satter,et al.  Nitrogen requirement and utilization in dairy cattle. , 1975, Journal of dairy science.

[29]  R. Palmer,et al.  Studies on the digestibility and utilization of the nitrogen of irradiated rumen bacteria by rats , 1971, The Journal of Agricultural Science.

[30]  D. Waldo.  Extent and Partition of Cereal Grain Starch Digestion in Ruminants , 1973 .

[31]  G. E. Mitchell,et al.  Ruminal and postruminal starch digestion in sheep. , 1968, Journal of animal science.

[32]  J. Russell,et al.  Effect of dietary corn starch intake on ruminal, small intestinal and large intestinal starch digestion in cattle. , 1981, Journal of animal science.

[33]  P. V. Soest,et al.  A net carbohydrate and protein system for evaluating cattle diets: I. Ruminal fermentation. , 1992, Journal of animal science.

[34]  R. H. Smith,et al.  Nucleic acid metabolism in the ruminant , 1971, British Journal of Nutrition.

[35]  G. E. Mitchell,et al.  Starch disappearance from different segments of the digestive tract of steers. , 1966, Journal of animal science.

[36]  J. Nocek.  Evaluation of Specific Variables Affecting In Situ Estimates of Ruminal Dry Matter and Protein Digestion1 , 1985 .

[37]  G. Hartnell,et al.  Determination of rumen fill, retention time and ruminal turnover rates of ingesta at different stages of lactation in dairy cows. , 1979, Journal of animal science.