Ruminal, intestinal, and total digestibilities of nutrients in cows fed diets high in fat and undegradable protein.

To study relationships of high undegradable intake protein and dietary fat on intestinal AA supply, the ruminal, intestinal, and total digestibilities of diets with or without added fat (5% of DM) and animal protein (blood meal: hydrolyzed feather meal, 1:1; 8% of DM) were examined with four cows in a 2 x 2 factorial design in a 4 x 4 Latin square experiment. Ruminal degradabilities were 14.9 and 18.6%, and intestinal digestibilities were 98.9 and 68.3%, respectively, for CP in blood meal and feather meal. Treatment effects on ruminal digestibilities were small. Protein supplementation increased total N intake by 29%, duodenal AA N flow by 39%, and AA N absorbed by 37%; absorption of Leu and Lys increased 60 and 33%, and absorption of Ile and Met increased 11 and 7%, respectively. Measured duodenal AA N flow (Cr2O3 marker) was 33% higher in cows cannulated adjacent to the pylorus compared with cows cannulated 100-cm distal to the pylorus, but only when cows were fed protein-supplemented diets; the estimates from those diets caused calculated microbial protein efficiency to exceed theoretical values. We postulated that blood meal and feather meal segregated near the pylorus, yielding high estimates of duodenal AA N flow. Removal of data for protein-supplemented diets obtained from cows cannulated at the pylorus yielded estimates of microbial protein synthetic efficiency consistent with literature values. Microbial synthesis of AA N was related linearly to ruminal digestion of carbohydrate. Location of intestinal cannulas may influence accuracy of nutrient flow estimates.