Estimation of daily flows of digesta in grazing sheep

Abstract

Chromium-51 and ruthenium-103 markers were infused constantly into the rumen of grazing sheep. Abomasal digesta were sampled every 3 h for 24 h, and the marker concentrations indicated that flow rates of organic matter (OM) and nitrogen (N) in both liquid (filtrate) and particulate (filtrand) fractions varied with time of sampling, generally by ¦30% from the values calculated from 24-h mean marker concentrations. The apparent flows were always least around midday and greatest after nightfall, possibly reflecting rumination. The patterns of variation, described by Fourier equations, did not differ significantly between sheep within experiments nor between the several types of pasture used, but there were changes in phase with time of year that corresponded with changes in the time of evening civil twilight. General equations were calculated to allow determination of mean daily OM and N flows from analyses of digesta samples taken at fixed times of day. Variation about the 24-h mean OM flow through the ileum was less than for the abomasum, and indicated that digesta took c. 3 h to pass through the small intestine. Variation in estimates of faeces OM and N excretion was small and essentially random. In two experiments, concentrations of 51Cr-EDTA in ruminal fluid during constant infusion varied by up to 15 % from the 24-h mean, which implied some changes in ruminal fluid volume.