THE EFFECTS OF INDIVIDUAL AND GROUP HOUSING ON SEXUAL-BEHAVIOR AND PREGNANCY IN PIGS

The effects of housing pigs in groups or tether-stalls during both a 2 week pre-mating and 6 week mating/gestation period on their sexual behaviour, fertility and fecundity were compared in a factorial experiment on a total of 82 pigs in three replicates. Pigs were housed either in groups or in tether-stalls of a design that was known to consistently result in a chronic physiological stress response. Premating housing treatment had no significant effects on any parameters measured and there were no interactions between pre-mating and mating/gestation housing environments. Housing pigs in tether-stalls during the mating/gestation period had adverse effects on both sexual behaviour and fertility. There was a lower proportion of pregnant pigs in tether-stalls (86 vs. 65%; P < 0.05) and this difference appeared to be due to trends for a lower proportion of pigs detected in oestrus (96 vs. 100%; P = 0.2), a lower proportion of matings which resulted in successful copulation (ejaculation of > 1.5 min) (88 vs. 94%, P = 0.2) and a lower pregnancy rate of mated pigs (72 vs. 88%; P = 0.07). Pigs in the tether-stall treatment were more restless (P < 0.05) during mating. Whereas the mechanism that results in a lower overall pregnancy rate in the tether-stall treatment may be a consequence of a stress response, and this needs to be confirmed, the result appears to be achieved through a combination of factors which individually are not significant, such as small reductions in sexual receptivity and fertility, which in combination result in an overall adverse effect on reproductive performance.