The composition of ingesta-digesta through the gastrointestinal tract of ruminant cattle

This study was conducted to determine the effect of dietary protein concentration on changes in composition of digesta, especially protein, in the gastrointestinal tract of ruminant cattle. Twenty eight steers were divided into seven groups of four steers each. Each group received one of seven experimental diets. Diets contained 20% cotton seed hulls, .1% chromic oxide, and varied stepwise in crude protein from 9 to 26% of dry matter (otherwise, diets were the same). Steerswere placed on their respective diet 12 to 18 days, then slaughtered approximately 12 hours after their last ad libitum feeding. The digestive tracts of the slaughtered steers were tied into eight segments: rumen, omasum, abomasum, three sections of the small intestine, cecum and large intestine. Subsamples from these segments were analyzed for pH, dry matter, crude protein, ash, acid detergent fiber, crude fiber, acid detergent fiber-nitrogen, soluble nitrogen and ammonia nitrogen. The ash, acid detergent fiber, pH, and dry matter composition of digesta were not affected protein concentration of the diet. However,there were significant changes in the concentration of these components as digesta passed through the tract. Crude protein, ammonia nitrogen, and acid detergent fiber-bound nitrogen tended to increase in the forestomachs and abomasum with increases in dietary protein. Changes in concentration of these components in the small intestines and hindgut were not consistent. Chromic oxide ratios indicated an average six fold dilution of dry matter from the omasum to the first-third of the small intestine. Crude protein increased dramatically in this segment while dry matter declined sharply. These changes were the result of endogenous secretions from the pancreas and intestinal glands.

Results of our analyses indicate that endogenous protein secreted into the duodenum of cattle, greatly exceeds the protein content of entering digesta. In light of this finding, protein absorption in the small intestine must be greater than previously thought. A trend for endogenous nitrogen concentration to increase with dietary crude protein concentration was not statistically significant.