Measuring supplement intake in the field using ytterbium as a marker

Abstract

Two experiments were conducted: pen experiment 1, to determine the distribution of the recovery over time of ytterbium (Yb) for diets with high and low dry matter digestibility; field experiment 2, to measure lupin seed intake using Yb as a marker. The diets in experiment 1 consisted of wheaten chaff plus lupins in the following amounts (g): 700 + 0,525 + 175, 175 + 525. The marker was applied using an adhesive solution made with methyl cellulose to which Yb acetate had been added. Total faecal collections were made for at least 5 days following feeding with the marked supplement. Mean retention time of Yb was not affected by diet in experiment 1. Estimated average lupin seed intake in experiment 2 was slightly less (9.5%) than expected from the difference between that offered and refused. Possible reasons for this difference include losses during handling (1.3%) and incomplete recovery (2.9%). It is concluded that the technique is suitable for estimating intake of lupin seed by sheep grazing in a group. A less laborious technique using faecal grab samples instead of total collections was evaluated and found to be unsuitable for estimating individual or group intakes. Faecal grab samples could be used to rank individuals on supplement intake.