The behavioural effects of undernutrition in confined farm animals.

Results suggest that where the animal is unable to engage in functional feeding to reduce nutrient deficit, it may still continue to engage in feeding by directing its feeding behaviour to other alternative stimuli. If feeding is to be maintained where there are constraints on further intake, the alternative stimuli to food must be of sufficient incentive to prevent feeding being inhibited by other tendencies. Alternatives to food then are likely to be chosen on the basis of their sensory (incentive) qualities, and the precise form of feeding behaviour will depend on the interaction between the feeding tendency and the choice of available stimuli. Growing pigs offered single diets ad lib. and experiencing relatively mild deficits of specific-nutrients, may direct this behaviour towards pen-mates as alternative foraging stimuli, with blood resulting from this foraging activity acting as a further incentive to sustain the behaviour. If specific-nutrient deficits in growing pigs are generally mild then feeding may only be sustained in the presence of high incentives such as pen-mates. However, it is not always clear why stimuli such as pen-mates continue to attract foraging activity when they provide little of the deficient nutrients underlying the behaviour. Where the nutrient deficit is more extreme, such as in food-restricted sows and broiler breeders even stimuli with low incentive (e.g. chains, bars or walls) may be sufficient to maintain feeding tendency. The environment, by only allowing simple and non-complex behaviour to be performed, channels the expression of feeding behaviour into simple and repetitive stereotypic behaviours. Other behavioural processes such as arousal and sensitization may facilitate the marked persistence of stereotypies.