Accuracy of the ytterbium-faecal index method for estimating intake of pasture-fed dairy goats
Résumé
There is no validated method for estimating pasture intake of dairy goats receiving concentrates and
grazing on multispecies swards. The objective of this study was to determine the accuracy of a method
based on estimates of faecal output (from ytterbium (Yb) oxide dilution), and of diet digestibility (from
faecal N concentration). Four indoor experiments with six goats each were carried out between 2014 and
2016, comparing several feeding management factors: concentrate supplementation level, diet feeding
level and pasture regrowth age. Actual daily intake, faecal output, in vivo diet digestibility, faecal N
concentration and faecal recovery rate of Yb were determined individually over five days at the end
of each period. Pasture intake was also estimated from faecal N and Yb concentrations. The relative
mean prediction error between actual and estimated pasture intake was low (7%), with no line or mean
biases, and a faecal Yb recovery close to 1.0. Random error came equally from the estimates of faecal
output and of indigestibility. It is concluded that the Yb-faecal index method is accurate and suitable
for estimating pasture intake of dairy goats grazing on multispecies swards whether or not supplemented
with concentrate.
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