Generalization of conditioned food aversions in grazing sheep and its implications for food categorization.

When grazing on heterogeneous pastures, herbivores may rely on food item generalization and categorization processes for reducing information processing while selecting their diet. The objective of this study was to assess the generalization of an aversion by grazing sheep for items differing by one or two criteria from an item against which they were negatively conditioned. Four items cultivated in pots were offered to the animals, resulting from the combination of an intrinsic criterion, i.e. grass species (ryegrass and fescue) and a transitory criterion, i.e. sward height (tall and short). We assessed the generalization process by comparing binary choices between the initially preferred tall ryegrass and the three other items, before and after animals had been partially conditioned against tall ryegrass. This method proved useful in assessing the generalization of an aversion. Sheep did not generalize their aversion on the basis of sward height but rather on species: they increased their preference for tall fescue and decreased their instantaneous preference for short ryegrass after having been conditioned against tall ryegrass. The generalization of an aversion through different states of a same species could indicate the possibility of a species-based categorization by grazing herbivores.