Effect of ruminally degraded protein on protein available at the intestine assessed using blood amino acid...

The effect of increasing amounts of ruminally degraded protein on protein available at the intestine was studied using the concentration of blood plasma branched-chain amino acids 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, coarsely ground corn, and 8% soybean meal (DM basis). Each experimental period was 17 d. Each period contained subperiods: 1 (5 d), 2 (5 d), and 3 (7 d). In addition to the basal diet, cows were given casein infusions of 0, .5, 1.0, 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 amino acids (Ile, Leu, and Val) in blood plasma increased as amounts of casein infused into the abomasum increased to the full amount. There was no increase in branch-chain amino acids when the same amount of casein was infused into the rumen, suggesting that ruminally degraded protein was adequate in the basal diet and the increased supply of degraded protein from ruminally infused casein did not increase the flow of protein to the small intestine.