Ruminal, intestinal, and total tract digestibilities of CP in grass, grass silage, and clover were measured using the mobile nylon bag method. Total tract indigestibilities measured with this method were compared with indigestible CP predicted by in vitro, 14-d ruminal incubation, and 12-h followed by 14-d ruminal incubation methods. Indigestible CP was related to chemical composition and harvest date. Ruminal disappearance of CP from nylon bags was 58, 71, and 58% for grass, grass silage, and clover, respectively. Intestinal CP disappearance was 84, 81, and 91% of escape CP, respectively. Lower ruminal disappearance was compensated by higher intestinal disappearance, resulting in a small variation in total tract indigestible CP within forage. Total tract indigestible CP was 7, 6, and 4%, respectively. Average total tract indigestible CP measured with the mobile nylon bag method (6%) was lower than that estimated by the in vitro (13%), 14-d ruminal incubation (14%), or 12-h ruminal incubation followed by 14-d ruminal incubation (11%) methods. All methods ranked forages similarly, resulting in high correlation coefficients among methods within forage. Total tract indigestible CP of grass, grass silage, and clover was related to CP content and harvest date, DM and ADIN content, and DM and CP contents, respectively.

SUMMARYThree ewes were intraduodenally infused with yeast RNA (15, 20 and 30 g/day) or control solutions for 3 days and the net changes in urinary allantoin excretion determined. Four mature wethers fitted with a re-entrant cannula in the proximal duodenum were fed two levels (0·66 and 1 × maintenance) of pelleted lucerne hay. Allantoin excretion was compared with total nucleic acid (NA) flow in the small intestine.The average proportion of the recovery of the infused RNA-N dose as urinary allantoin–N amounted to 0·119 ± 0·0046. The values of the net increase of allantoin-N (Y, g/day) above control levels were highly significantly correlated (n = 12, r = 0·98) with amounts of RNA-N infused (X, g/day): y = 0·1185 (± 0·0086) X–0·004 (P < 0·001). The average ratio of urinary allantoin-N to NA-N passing the duodenum during 24 h was 0·173. A difference between the two conversion factors is discussed in relation to endogenous allantoin excretion and purine base composition of yeast and bacterial RNA.

No abstract

No abstract

Urinary allantoin, an end product of purine base metabolism, originates in sheep from three possible sources: exogenous, purine bases of rumen microorganisms and feed purines and ureides, and endogenous, purines catabolized in tissue turnover. Earlier studies suggested that nucleic acid purines of rumen micro-organisms may be a predominant source of urinary allantoin (Antoniewicz, Heinemann & Hanks, 1979, 1981).