Skip to main content
ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #60883
Title: EFFECT OF RUMINALLY DEGRADED PROTEIN ON PROTEIN AVAILABLE AT THE INTESTINE ASSESSED USING BLOOD AMINO ACID CONCENTRATIONS

Author
item DHIMAN, TILAK - UNIV OF WISCONSIN-MADISON
item Satter, Larry

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Ruminant animals obtain amino acids, the building blocks for protein, from dietary protein that escapes degradation in the forestomach (rumen), and from microbial protein synthesized during fermentation digestion, also in the rumen. Some evidence in the scientific literature suggests that microbial growth is stimulated by several nitrogen sources (peptides, amino oacids, ammonia) at much higher concentrations in the rumen than previously thought. To test this, a soluble protein source was constantly infused into the rumen to increase nitrogen supply to the microorganisms. Concentrations of branched chain amino acids were measured in blood plasma as an indirect measure of microbial protein synthesis in the forestomach. Results demonstrated that adding nitrogen sources to the rumen over and above what the National Research Council recommends as minimally needed is without benefit. This information will help in formulation of dairy diets that are more profitable and result in mineral loss of nitrogen to the environment.

Technical Abstract: The effect of increasing amounts of ruminally degraded protein on microbial protein synthesis was studied using the concentration of blood plasma branched-chain AA as an indicator of protein flow to the small intestine. Five ruminally cannulated cows in midlactation were used in a 5 x 5 Latin square design experiment and were fed a diet containing 20% alfalfa silage, ,40% corn silage, 30% shelled coarse ground corn, and 8% soybean meal (dry basis). Each experimental period was 17 d. Within each period there were subperiods 1, 2, and 3 of 5, 5, and 7 d, respectively. In addition to the basal diet, cows were given casein infusions: 0, .5, 1.0, 1.5, and 2.0 kg/d. During subperiod 1, the full amount of casein was infused into the abomasum (A100); in subperiod 2, 10% of each casein level was infused into the abomasum (A10); and during subperiod 3, the full amount of casein was infused into the rumen (R100). The concentration of branched-chain AA (Ile, Leu, and Val) in blood plasma increased with increasing amounts of casein into the abomasum (A100). There was no increase in branched-chain AA when the same amount of casein was infused into the rumen (R100), suggesting that ruminally degraded protein was adequate in the basal diet, and the increased supply of ruminally degraded protein from ruminally infused casein did not increase microbial protein synthesis.