Glycosyl ureides in ruminant nutrition. 3. In vivo studies on the metabolism of glycosyl ureides and corresponding mixtures of their free component molecules.

1. Steers and sheep were given basal diets of barley and straw (1:1, w/w), usually containing urea, which for certain experimental periods were supplemented with pure glucosyl urea (GU), pure lactosyl urea (LU) or a product prepared from whey concentrate (EW) which contained 65-80% of the lactose in the form of LU. 2. On the morning of an experiment ureide (or EW) was omitted from the feed and a dose of either ureide (or EW) or equivalent amounts of free lactose and urea (L + U) was added to the rumen within 30 min of feeding, together in some experiments with polyethylene glycol (PEG) as a fluid-phase marker. Samples of rumen contents, and in some experiments abomasal contents, were taken at intervals for up to 8 h. 3. For both steers and sheep given GU and LU for the first time (unadapted animals) there was little or no accumulation of ammonia in the rumen or cleavage of the sugar-urea bond. Galactose was, however, slowly liberated from LU. 4. For steers and sheep which had been given GU, LU or EW for approximately 7-10 d or more (adapted animals) some accumulation of ammonia occurred after adding GU or LU to the rumen, but for LU it occurred less rapidly and to a lower peak concentration than when L + U was added. In adapted animals cleavage of the sugar-urea bond in LU was virtually complete in 2-4 h. Degradation of the components of L + U was virtually complete within 1 h. 5. Recovery at the abomasum of ureide (present either as GU or LU) estimated from ureide: PEG values, appeared to be complete in experiments with unadapted sheep given a dose of EW. In adapted sheep only very small amounts of ureide in an EW dose (on average 6%) entered the abomasum undegraded. Amounts lost in this way appeared to be positively correlated with the rate of fluid turnover in the rumen.