a1 National Institute for Research in Dairying, Shinfield, Reading RG2 9AT
1. The fate of glucosyl urea (GU), lactosyl urea (LU) and corresponding mixtures of the free sugars and urea and their degradation products were examined during in vitro incubation of the compounds with rumen contents taken from donor sheep and steers at various stages of adaptation to these compounds.
2. The sugar–urea bond was virtually unattacked in rumen contents from unadapted sheep and steers but generally a slow release of the galactose moiety occurred. After feeding LU or GU to animals for a period of approximately 10 d, the rates of disappearance of both bound urea and sugar had increased, but were still markedly slower than those of the corresponding free sugars and urea. In vitro rates of degradation of both free lactose and urea also increased in response to the feeding of lactose and urea to rumen contentdonor animals.
3. Ammonia accumulation in rument contents when GU or LU were the substrates was notably lower than when equivalent amounts of glucose and urea or lactose and urea were the substrates.
4. Bacterial growth was estimated using an vitro method based on incorporation of 32P into bacterial nucleic acids. Markedly different patterns of bacterial growth were observed depending on whether LU or lactose and urea were the substrates.
(Received July 27 1981)
(Accepted January 27 1982)