Behavioural responses affecting gilt and sow reproduction.

Behavioural responses can have direct effects on reproduction when the performance of the behaviour contributes to productivity (e.g. achievement of copulation). Alternatively, there are indirect effects where a behavioural change is insufficient to allow adaptation to an environmental change and so the animal has to resort to physiological mechanisms with potential adverse effects on productivity. Boar contact has substantial effects on a number of female behaviours that can directly affect her productivity. Either daily introduction to a boar or continuous housing adjacent to boars is effective in stimulating the onset of oestrus in weaned sows. In addition, daily boar contact is necessary to maintain ovarian activity in post-pubertal gilts. The efficiency of the back-pressure test (BPT) in detecting sexually receptive females depends on females receiving intense and close boar contact at the time of testing. However, there are situations in which continuous stimulation from boars may adversely affect sexual behaviour; continuous housing of gilts adjacent to boars, with a wire-mesh division separating them, reduces the efficiency of detection of oestrus by means of the BPT or a boar. There is some evidence to indicate that housing weaned sows adjacent to boars may adversely affect the duration of oestrus but not detection rate of oestrus. The effects of female contact on productivity are generally indirect with physiological responses (rather than behavioural responses) to suboptimal group size, space allowance or housing system predominantly responsible for any adverse effects on reproduction. The literature on the effects of individual or group housing on reproduction is equivocal, but there is a trend for a reduced conception rate or pregnancy rate in individual housing. Group size and space allowance may affect the efficiency of detection of oestrus. A space allowance of 1 m2/animal appears to affect detection of oestrus adversely for gilts, probably via a chronic stress response associated with overcrowding. The literature on the effects of group size on sexual behaviour of female pigs is also equivocal, perhaps because in some studies there were suboptimal space allowances. Nevertheless, there appear to be problems with detection of oestrus in very small groups and in large groups. The effects of human contact on female reproduction are indirect. There are no direct effects on the sexual behaviour of female pigs and the effects on reproduction are probably mediated by a chronic stress response. High levels of fear of humans may depress the reproductive performance of pigs and this fear response is probably affected by the behaviour of the stockperson.(ABSTRACT TRUNCATED AT 400 WORDS)