Faecal output of grazing sheep measured by total collection or using chromium sesquioxide

Abstract

Controlled release devices (CRDs) delivered chromium sesquioxide into the rumen of grazing sheep, and estimates of faecal output were made using the specified release rate and this rate adjusted according to the number of days to expiry of each CRD. Release of chromium from CRDs ceased at different times, varying from 26 to over 35 days after administration. There were positive ( P < 0.001) linear relationships between estimates of faecal DM output made using CRDs and measured outputs in three experiments. Although the relationships were improved (Expt. 1: slope 0.78 vs. 0.73, r=0.92 vs. 0.88; Expt. 2: slope 1.00 vs. 0.88, r=0.94 vs. 0.92; Expt. 3: slope 0.94 vs. 0.86, r=0.93 vs. 0.86) by using release rates corrected for time to expiry, compared to specified release rates, the regression coefficients for the two techniques were not significantly different. Relationships between total faecal collection and estimates for individual sheep across all experiments were improved (slope 1.01 vs 0.85, r = 0.95 vs. 0.91, P < 0.05) by adjusting the release rates using expiry information. Despite this, estimated faecal DM output did not differ significantly from measured DM outputs in these experiments. It is concluded that CRDs can be used to give reasonable estimates of faecal DM output for groups of grazing sheep, but total collection from animals adapted to harnesses may be easier and more accurate.