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The pig provides many examples of how principles of behavioural ecology and sociobiology can lead to insights into farm animal behaviour. According to parent-offspring conflict theory, parents should tend to give a level of parental investment somewhat below that solicited by the young. When closely confined during lactation, sows can do little to limit the amount of contact with the piglets, and the young stimulate a prolonged, high level of lactation. Certain alternative housing systems allow the sow to limit the stimulation she receives, and the resulting reduction in lactation can actually be advantageous to both parties. Communal care of offspring has both advantages and disadvantages in various species; these may help to explain why communal care occurs to a limited extent in pigs, and why sows isolate their litters in early lactation. Neonatal competition and mortality among newborn piglets have strong parallels in the “facultative siblicide” which adjusts brood size in numerous species of birds. These species typically produce slightly more young than are normally raised, and the number of siblings that survive is determined by the ability of the smaller young to withstand intense competition. The hypothesis that pigs have evolved a similar system of brood reduction may explain why piglet mortality is such an enduring problem and requires solutions different from those that work for other domestic species. Resource defence theory provides a functional framework for studies of aggressive behaviour. Factors determining the defensibility of a resource include its degree of clumping in time and space, and these suggest ways to reduce competition for food and other resources. However, aggression involved in establishing social dominance is more likely to be influenced by manipulating traits of the competing animals (competitive ability, familiarity) rather than the defensibility of resources. We conclude that principles of behavioural ecology and sociobiology provide a useful functional and evolutionary perspective to complement other approaches to the study of farm animal behaviour.


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