Effects of oestrogen supplementation and space restriction on PGF(2 alpha)-induced nest-building in pseudopregnant gilts

This study examined the role of oestrogen supplementation on PGF(2 alpha)-i nduced nest-building in pseudopregnant gilts. Oestradiol valerate (5 mg/day ) injections were given on Days 11-15 of the oestrous cycle to induce pseud opregnancy. A further series of injections of either oestradiol valerate (5 mg/day) or vehicle were given on days 44-46 of pseudopregnancy to reflect more closely the hormone profile seen in pregnancy. Nest-building was induc ed by a single intramuscular injection of 15 mg of PGF(2 alpha) (Lutalyse) on Day 47 of pseudopregnancy. The gilts were housed in pens (2.8 X 1.7 m) c ontaining straw in experiment I or chronically confined in crates (0.6 X 1. 7 m) that did not contain straw on days 44-48 of pseudopregnancy for experi ment 2,. Oestrogen supplemented gilts had significantly higher concentratio ns of circulating 17 beta-oestradiol on day 47 of pseudopregnancy but there were no significant differences between treatments for circulating levels of prolactin, progesterone, cortisol or oxytocin, or for any behavioural me asure in either experiment. These results indicate that there is no direct effect of supplementing already pseudopregnant gilts with oestradiol valera te on PGF(2 alpha)-induced nest-building. The results also show that the pr e-partum environment has a pronounced effect on nest-building behaviours an d that non-pregnant pigs might be a useful model for pre-partum nest-buildi ng in this species. (C) 1999 Elsevier Science B.V. All rights reserved.