[Effect of the content of crude plant protein in feed on the utilization of urea in dairy cattle. 4. Passage of amino acids through the duodenum].

Model investigations carried out by means of a re-entrant method at the duodenum with dairy cows and with energy-equivalent rations (600 EFU cattle/kg DM), which after the supplementation of 11 g urea/kg DM (150 g/animal and day) contained 13.8 (I), 16.7 (II) and 20.2 (III)% crude protein, had the following results: The amino acid profile of the duodenal protein differed from that of the applied rations and was similar to the microbial protein in the rumen. It only changed inconsiderably with the protein level of the ration. There were differences between the amino acids of the feed as to their apparent rate of fermentation in the rumen. Ser, tyr, lys, and leu apparently proved to be most resistent whereas arg, asp, met, ile and phe were apparently fermented for the most part or completely. The passage rate of amino acids at the duodenum related to intake were, from I ... III 126, 102 and 87%. With all rations there were always net losses of some amino acids (his, arg) and net gains (lys, thr, ser, gly, val, met and tyr) at the duodenum in comparison intake. 15N from urea was incorporated into all the amino acids determined in the duodenal protein, most intensively into glu, ser, asp, ile, gly, his and leu. The apparent digestibility of the total amino acids in the intestines was independent of the crude protein level of the rations and reached 69 ... 71% with a deviation range of 59 ... 81% for the individual amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)