[Determination of true digestibility of amino acids from the small intestine of dairy cows].

True digestibility of 17 amino acids was determined with 2 lactating cows, fitted with rumen fistulae and T-shaped cannulae at the proximal duodenum and terminal ileum. The calculations were based on the following regression equation: I = a + b x D + c x PFT, with I = amino acid flow at the ileum, D = amino acid flow at the duodenum, and PFT = passage of non-protein dry matter at the ileum. As the factor b means the part of undigested amino acids, 1 - b represents the true digestibility. The calculations, which comprize the results of 16 individual experiments, showed that lysine, histidine, arginine, cysteine, leucine, isoleucine and tyrosine were absorbed in the range of 85% to 90%. Lowest absorption-rates (77-80%) were found for threonine, valine, methionine, aspartic acid and serine. The overall true digestibility of amino acids was 83% without any difference between essential and not essential amino acids.