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-parturie nt surge in prolactin. There is concern that sows in crates may experi ence psychological stress as a result of physical interference with ne st-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 o f movement with bedding (treatment P; n=17). The animals were blood sa mpled on the day before and the day after introduction to the treatmen ts. Blood and behaviour sampling was resumed 48 h before EPD and conti nued until 4 h post-commencement of farrowing. As with previous studie s gilts in both environments were more active (P<0.001) and performed more substrate-directed behaviour in the pre-parturient period (P<0.00 1). Gilts in pens spent considerable amounts of time in straw-directed behaviour, and gilts in crates increased amounts of floor- and fixtur e-directed behaviour (both P<0.001). Prolactin was not affected by tre atment and increased in both environments over the same time period as this substrate-directed behaviour. However, the causal role of prolac tin in nest-building must now be questioned given that a number of ind ividuals 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 a lso increased in penned animals during parturition. There were no cons istent correlations among behaviour, prolactin and cortisol. The gener al increase in cortisol in the early post-partum period may suggest th at parturition in itself has stress-inducing aspects. The additional r ise in cortisol found in the crated sows may indicate that the close c onfinement of the crate, by interfering with the expression of materna l behaviour, induces psychological stress. There was no evidence that the elevated cortisol response in crated gilts extended beyond the end of parturition.