The use of tritiated gypsum for estimating individual intakes of pelleted or unpelleted supplement by lambs fed individually or in groups

Abstract

Grazing lambs, fed either individually or in groups, received daily supplements of 400 g/lamb of pelleted or unpelleted sunflower meal (SFM), labelled with tritiated gypsum. For pelleted SFM, individual and group intakes, estimated from the accumulation of tritium in the body water pool, were 1.5% and 3-5% less respectively than measured intakes. However, for unpelleted SFM, estimated intakes were 3-24% less than measured intakes. In a second experiment, lambs were individually fed labelled, unpelleted SFM indoors to examine possible losses of radioactive label which might account for the discrepancies observed in experiment 1. Loss of label in water bowls and in SFM adhering to the food bins reduced the effective specific activity of the food consumed by only 0.2%. Estimated intakes were closely related to known intakes by a regression in which the slope did not differ significantly from 1.0 nor the intercept from zero. It is concluded that the low estimates of unpelleted SFM intake in the first experiment are real and reflect wastage of supplement. It follows that the tritiated gypsum technique is equally applicable to pelleted and unpelleted supplements, and may be of greater use with the latter where wastage may be greater.