Endogenous amino acid flow in the duodenum of dairy cows

The endogenous nitrogen (N) and individual amino acid how to the distal duodenum were estimated in lactating cows fed diets low in amino acid content. Three duodenal cannulated cows were used in a 3 x 3 Latin square with different concentrate to roughage ratios as treatments. Diets were composed of straw, starch, molasses and urea. The duodenal flow of endogenous protein was estimated by the difference method (total flow - microbial flow - undegraded feed flow) and by the amino acid profile method taking different protein contributors into account. The mean endogenous flows of N, non-ammonia N (NAN) and amino acid N (AAN) were 135 +/- 16, 12 +/- 18 and 69 +/- 13 g day(-1), when estimated by difference. These endogenous flows constituted about one-third of the total flow of nitrogen, NAN and AAN, respectively. The endogenous AAN flow constituted about 25% of the total flow of AAN, when estimated by the amino acid profile method. The Variation between and within cows was substantial and could not be related to feeding. Glycine constituted about 30% of endogenous amino acids, owing to the content of bile.