Untersuchungen zur Überführung von Harnstoff-Stickstoff aus dem Darm in die Mägen bei der Milchkuh

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Abstract
In 2 experiments each with 1 dairy cow the utilization of urea-N after its ruminal or duodenal infusion was comparatively investigated on 2 crude protein levels and different urease activities in the rumen. The rations contained 9.6 (I) and 14.3 (II) g crude plant protein/100 g dry matter. After completed adaptation 50 g urea were daily infused in the rumen (R, via cannula) in 3 h the duodemun (D, distal cannula of the reentrance cannula) in 6 h with the morning and evening feeding. In experiment II the urease blocker phosphoric acid phenylester diamide (D/PPD) was applied in an additional experiment synchronously with the duodenal urea application. On the 1st measuring day in each case the urea in the morning feeding was labelled with 17.4 atom% 15N-excess (15N''). Measuring results in the sequence I R, I D, II R, II D, II D/PPD: 15N''-passage rate at the duodenum within 72 h in the TCA-soluble N-fraction 29, 18, 24, 13 and 16, in the TCA-precipitable N-fraction 59, 25, 41, 11 and 5% of the application, 15N''-excretion within 96 h in milk protein 6.8, 4.2, 4.6, 3.4 and 1.9, in feces 20, 12, 19, 8 and 4, in urine 20, 32, 34, 56 and 75% of the application, 15N-balance 59, 56, 47, 36 and 24% of the application, passage rate of non-NH3-N in the duodenum 134, 118, 96, 107 and 99% of the total N-intake. After ruminal infusion there always was a higher NH3-concentration in the rumen and 15N-frequencies in the rumen proteins. Urea-N that gets into the intestines is to a low degree used for duodenal protein supply as directly utilizable urea-N from the ration in the rumen. The difference increases with the protein content of the ration and the inhibition of rumen ureas. The urea N-balance is to a considerably smaller degree influenced by the place of urea infusion particularly at a low level of N-supply, which is due to a better utilization of the urea-N transported with intermediary metabolism from the intestines. The role of urease as a regulator of urea transport through the rumen wall cannot be corroborated.