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The nutritional choices of farm animals: to eat or what to eat?

  • I. Kyriazakis (a1)

Irrespective of whether farm animals are given access to a single homogeneous food or to two or more heterogeneous foods as a choice, their feeding behaviour raises one of two questions (i) how much to eat, and (ii) what to eat? Despite frequent comment to the contrary, their feeding behaviour appears to be goal-orientated rather than random or purposeless. I therefore consider first the goals of farm animals in relation to their feeding behaviour. In general it is accepted that the overall biological framework in which all animals are trying to maximize fitness’ also applies to farm animals. However, some modification is called for in order to account for those situations in which intensive genetic selection has led to relatively ‘unfit’ reproducing animals and for those cases where animals are given access to foods which have not figured in their evolution

On the basis that feeding behaviour is goal orientated, I then consider whether farm animals achieve their goals by monitoring their behaviour in the short or longer term. The conclusion drawn is that while short-term feeding behaviour may be a device to exploit the feeding environment effectively, it is largely unrelated to short-term fluctuations in an animal’s internal state. By contrast, longer-term feeding behaviour is very closely related to longer-term change in internal state, implying the maintenance of close control over feeding behaviour in terms of food intake and diet selection. All animals, including farm animals, are considered to be creatures of habit which maintain habitual feeding behaviour until a change is provoked by a significant alteration in their internal state. Such an alteration requires to be of significantly large magnitude and to be unlike the usual short-term, systematic fluctuations which occur over a day in the profiles of metabolites or hormones. Based on this premise, I contend that the mechanisms by which these disturbances are perceived by the animal will be general rather than specific. The notion that animals can fully achieve their goals by monitoring their feeding behaviour is obviously applicable in situations where they are given appropriate nutritional choices. Where animals are given inadequate or inappropriate choices, as is predominantly the case with farm animals, their feeding behaviour is designed to bring them as close as possible to their goals. Finally I consider the relevance of nutritional choices to farm animals by addressing the possibility of exploiting the goal orientation of feeding behaviour. I conclude that greater recognition of the goal-orientated nature of farm animals’ feeding behaviour can bring benefits in three areas: (i) improved biological understanding of animals’ goals; (ii) improved animal welfare; and (iii) improved animal performance.

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