Isobutylidendiharnstoff als NPN-Quelle für Wiederkäuer

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Abstract
Two cows with rumen cannulae and duodenal re-entrant cannulae received a conventional diet on the basis of a mixture of maize silage, hay and concentrated feed and, after a 3 wk adaptation to isobutylidene diurea (IBDU) (276 g/animal per day), 138 g IBDU with 3.865 mg 15N-excess as a single supplementation to their 1st meal. After a 6 wk break the same cows served a repeated experiment without IBDU adaptation. Irrespective of the adaptation, a re-increase of the 15N-labeling in the TCA[trichloroacetic acid]-soluble N in the rumen could be proved between 6-8 h after the intake of the isotopes, which resulted from the backflow of 15N to the rumen. In the duodenal digesta the maximum labeling of the TCA-soluble N-fraction appeared 12 h after the intake of the isotopes. At that moment a labeling plateau began in the protein fraction, which lasted to the 36th h. On an average of all 4 cows .apprx. 30% of the 15N taken in the TCA-precipitable fraction and 55-60% in the TCA-soluble fraction had passed the duodenum up to the 72nd h after the beginning of the experiment. Up to the 72nd h of the experiment, .apprx. 15% was excreted in urine, .apprx. 16% in feces and .apprx. 7% in the milk. Roughly 1/2 of the 90% 15N-amount measured at its passage in the re-entrant cannula (related to the intake) apparently was metabolized in the rumen at least twice, or after the 1st passage through the duodenum it origined from the intermediary metabolism (e.g., amino acids and their incorporation as digestion secretions). There were negative correlations between the rumen fluid pH and the 15N incorporation in the rumen proteins, and 15N-excretion through the TCA-soluble and -precipitable quota of feces. An adaptation to IBDU appears unnecessary.