Accuracy of the ytterbium-faecal index method for estimating intake of pasture-fed dairy goats

There is no validated method for estimating pasture intake of dairy goats receiving concentrates and\ngrazing on multispecies swards. The objective of this study was to determine the accuracy of a method\nbased on estimates of faecal output (from ytterbium (Yb) oxide dilution), and of diet digestibility (from\nfaecal N concentration). Four indoor experiments with six goats each were carried out between 2014 and\n2016, comparing several feeding management factors: concentrate supplementation level, diet feeding\nlevel and pasture regrowth age. Actual daily intake, faecal output, in vivo diet digestibility, faecal N\nconcentration and faecal recovery rate of Yb were determined individually over five days at the end\nof each period. Pasture intake was also estimated from faecal N and Yb concentrations. The relative\nmean prediction error between actual and estimated pasture intake was low (7%), with no line or mean\nbiases, and a faecal Yb recovery close to 1.0. Random error came equally from the estimates of faecal\noutput and of indigestibility. It is concluded that the Yb-faecal index method is accurate and suitable\nfor estimating pasture intake of dairy goats grazing on multispecies swards whether or not supplemented\nwith concentrate.