THE EFFECT OF ENVIRONMENT ON BEHAVIOR, PLASMA-CORTISOL AND PROLACTIN IN PARTURIENT SOWS

Nest-building in the pig is thought to be stimulated by a pre-parturient surge in prolactin. There is concern that sows in crates may experience psychological stress as a result of physical interference with nest-building. Thirty-three gilts were implanted with jugular catheters approximately 10-14 days before expected date of parturition (EPD). On day 5 before EPD, gilts were moved into either conventional farrowing crates without bedding (treatment C; n=16) or pens allowing freedom of movement with bedding (treatment P; n=17). The animals were blood sampled on the day before and the day after introduction to the treatments. Blood and behaviour sampling was resumed 48 h before EPD and continued until 4 h post-commencement of farrowing. As with previous studies gilts in both environments were more active (P<0.001) and performed more substrate-directed behaviour in the pre-parturient period (P<0.001). Gilts in pens spent considerable amounts of time in straw-directed behaviour, and gilts in crates increased amounts of floor- and fixture-directed behaviour (both P<0.001). Prolactin was not affected by treatment and increased in both environments over the same time period as this substrate-directed behaviour. However, the causal role of prolactin in nest-building must now be questioned given that a number of individuals showed no increase in prolactin over the 48 h before EPD, but still showed an increase in substrate-directed activity. Cortisol was strongly affected by treatment with treatment C having elevated total cortisol over much of the pre-parturient period (P<0.001). Cortisol also increased in penned animals during parturition. There were no consistent correlations among behaviour, prolactin and cortisol. The general increase in cortisol in the early post-partum period may suggest that parturition in itself has stress-inducing aspects. The additional rise in cortisol found in the crated sows may indicate that the close confinement of the crate, by interfering with the expression of maternal behaviour, induces psychological stress. There was no evidence that the elevated cortisol response in crated gilts extended beyond the end of parturition.