Untersuchungen zum Einfluß des Gehaltes an pflanzlichem Rohprotein in der Ration auf die Verwertung von Harnstoff bei der Milchkuh

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Abstract
Model investigations carried out by means of a re-entrant method at the duodenum with dairy cows and with energy-equivalent rations (600 EFUcattle/kg DM [dry matter]), which after the supplementation of 11 g urea/kg DM (150 g/animal and day) contained 13.8 (1), 16.7 (2) and 20.2 (3) % 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. Serine, tyrosine, lysine and leucine apparently proved to be most resistant arginine, asparagine, methionine, isoleucine and phenylalanine were apparently fermented for the most part or completely. The passage rate of amino acids at the duodenum related to intake were 126, 102 and 87%. There were always net losses of some amino acids with all rations (histidine, arginine) and net gains at the duodenum in comparison intake. 15N from urea was incorporated into all the amino acids determined in the duodenal protein, most intensively into glutamine, serine, asparagine, isoleucine, glycine, histidine and leucine. 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. Of the essential amino acids digested in the intestines, valine, histidine, methionine and phenylalanine were represented in the milk protein with the highest quotes. The utilization rates of the duodenal amino acids for maintenance and the synthesis of milk protein was calculated for 1, 2 and 3 at 0.45, 0.42 and 0.39, in which changes in live weight were not taken into account.