Short-term choices of cattle vary with relative quality and accessibility of two hays according to an energy gain maximisation hypothesis
2002
We studied how feeding choices of cattle evolved when the difference in quality between two forages, and the accessibility of the better one, were simultaneously varied. In an indoor experiment, nine Aubrac heifers were offered a choice between two of three different hays, designated good (G), coarse 1 (C1) and coarse 2 (C2). These last two hays differed in botanical composition but were similar in nutritive value. In 10 min tests, the poorer quality hay was offered ad libitum, and the animal had to walk across the test area to obtain a small quantity of the better one. For each association GC1, GC2 and C1C2, three quantities of the better hay (G or C1 for C1C2) were used to vary its accessibility. Choice of the better hay was quantified as the proportion of total active time spent walking for and eating it. Heifers not only perceived the quantity of hay for which they walked, switching to the poorer one when better hay accessibility decreased, but also the magnitude of difference in quality between the offered forages, walking less for the better one when this difference was small (C1C2) and behaving in the same way when the magnitudes were similar (GC1 versus GC2). Overall choices were best described by a sigmoidal relationship with the ratio of energy gain on each forage, according to a maximization hypothesis. Choices were, however, suboptimal, especially for the C1C2 association. This was probably due to the heifers' need to evaluate each alternative, or because, even at this short time scale, they wanted to diversify their diet. The asymptotic value of this sigmoidal curve corresponds to the choice measured at a daily scale with the same associations of hays, without any accessibility constraint. Short-term choices between hays measured with a learning procedure would thus allow animals' daily preferences to be estimated.
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