The Effect of Pattern of Feeding on the Development of Food Preferences in Goats in Response to Positive and Negative Post-ingestive Consequences

摘要

Free-ranging ruminant herbivores generally encounter a variety of plant species that they could potentially include in their diet. Some of these plants may be toxic to various degrees due to the presence of plant secondary compounds. Plant species andplant parts also vary in their nutrient composition. Foraging herbivores are thus faced with choices as they graze which will influence the risk of toxicity as well as the nutritional rewards they gain from consuming particular plants. Previous observational studies indicate that herbivores generally select a diet richer in nutrients than the average nutritional composition of the available vegetation (Murden and Risenhoover, 1993). Similarly, although herbivores sometimes experience toxic symptoms asa result of consuming particular plants, they are generally reasonably adept at avoiding toxicity by selecting plants with low levels of secondary compounds (Foley et al., 1999). Recent evidence suggests that one means by which herbivores are able to make appropriate diet choices is by learning about the nutritional and toxic consequences of consuming particular plants (Provenza, 1995). Thus, animals learn to associate positive and negative post-ingestive consequences with the flavour and other sensoryproperties of the plant. Such conditioned food aversions and preferences have been convincingly demonstrated in pen-fed situations with ruminants where simple, generally two-way choices, are made between foods associated with different post-ingestive effects (Zahorik et al., 1990). The situation with free-ranging herbivores is more complex however, with animals often encountering a number of different plant species within a single feeding bout.