Quantitative Studies on Amino Acid Absorption in Sheep

Abstract

Mature Hampshire wethers were used to study several aspects of amino acid absorption in sheep. Net absorption values (absorption minus utilization by the gut wall) were the product of the portal blood flow (measured by the Doppler-shift technique) and portal-carotid concentration differences. When two wethers were fed 50 g dry matter/kg^0.75/day and 60 g dry matter/kg^0.75/day of chopped alfalfa hay once daily, net absorption was positive at 2, 6 and 10 hours after feeding in one sheep, and 0, 2 and 10 hours after feeding in another. At all other sampling times net absorption was negative, suggesting substantial utilization of absorbed amino acids by the gut wall. When the same ration was fed at 2-hour intervals, there was no consistent pattern in net amino acid absorption. In three wethers fed 60 g dry matter/kg^0.75/day of chopped alfalfa hay at 2-hour intervals, mean net absorption of total amino acids was 48.9 ± 13.42 g/day (22.2 ± 8.64 g essential, 26.7 ± 4.97 g nonessential), approximately 50% of the daily intake. The individual essential amino acids were absorbed in ratios similar to those found in rumen bacterial protein. Of the nonessentials, aspartate and glutamate were absorbed to a lesser extent and proline and alanine to a greater extent than their proportions in rumen bacterial protein. In two wethers fed the same ration and infused per abomasum with 0, 10 or 30 g L-leucine/day, net absorption of leucine increased only at the highest level of infusion (P < 0.01). Infusion of leucine depressed the concentration of several of the other amino acids in portal and/or carotid plasma, but depressed net absorption of only lysine (P < 0.05).