Prostaglandin F2alpha-induced nest-building in pseudopregnant pigs. I. Effects of environment on behaviour and cortisol secretion.

Pigs may be susceptible to stress when they are strongly motivated to nest-build in a space-restricted environment. This study aimed to explore whether nest-building behaviour could be induced by prostaglandin F2alpha (PG) administration to pseudopregnant gilts and to determine whether induced behaviour and cortisol output differed between animals chronically placed in either farrowing crates or pens. Jugular vein catheters were placed on Day 39 of pseudopregnancy and blood samples collected daily from Day 40 to Day 48. On Day 42, gilts were either restricted to farrowing crates 1.6 x 0.6 m with no straw (C: n = 11) or left in pens 2.8 x 1.74 m with straw (P: n = 11). On Day 47, blood and behaviour sampling was from 90 min pre-PG (Dinoprost; Lutalyse, Upjohn, Kalamazoo, MI) to 6 h post-PG. PG injection successfully induced nest-building behaviour in P gilts within 15 min of injection. Penned gilts engaged in more straw/floor-directed behaviour than C gilts (p < 0.01), whereas attempts in C gilts seemed partial or incomplete. Conversely, C gilts showed increased (p < 0.05) amounts of fixture-directed behaviour, whereas P gilts did not post-PG. For both groups, cortisol increased significantly (p < 0.05) post-PG compared to pre-PG values. Cortisol concentrations in C gilts were significantly greater than in P gilts prior to and after PG (p < 0.05) on Day 47, whereas there were no significant differences in concentrations of cortisol between C and P on other days. These results demonstrate that PG can induce nest-building behaviour in the absence of foetal signals. Whereas the pseudopregnant gilt seemed to chronically adapt to the imposition of a farrowing crate, gilts subsequently attempting to nest-build showed increases in cortisol output when compared to their penned counterparts, suggesting that a stress was imposed by the space-restricted environment.