Effects of ovariohysterectomy on prostaglandin F2alpha-induced nesting behaviour in pigs

Exogenously administered prostaglandin (PG) F2alpha induces behaviour similar to prepartum nest building in pregnant, pseudopregnant and nonpregnant female postpubescent pigs (Sus scrofa). These effects may be regulated by PGF2alpha-induced endocrine changes within the reproductive tract, such as those that initiate luteolysis. This study investigated the short-term effects of ovariohysterectomy on PGF2alpha-induced nesting behaviour in nonpregnant females. Cyclic 9-month-old virgin female pigs (gilts) received an oral dose (20 mg/day) of a synthetic progestogen (altrenogest; Regumate porcine, Hoechst, Milton Keynes, UK) for 18-21 days to synchronize oestrus. The gilts were then ovariohysterectomized (n=8) or sham-operated (n=7) on Days 3-8 after oestrus. They were housed individually and initially subjected to a series of control behavioural tests to establish the effect of ovariohysterectomy on their responses to the experimenters, novel objects, straw bedding and space restriction. Ovariohysterectomized gilts had a shorter latency to approach the experimenters than sham-operated animals, but there were no differences in their responses to a novel object, straw bedding or space restriction. Twelve to 16 days after oestrus, corresponding to the midluteal phase in sham-operated gilts, they were treated intramuscularly with 15 mg PGF2alpha (0.12 mg/kg, dinoprost; Lutalyse, Upjohn, Crawley, UK). PGF2alpha treatment induced a significant increase in straw gathering in ovariohysterectomized but not in sham-operated gilts. Other nesting behaviours, including rooting and pawing at straw, were induced in all animals. These results show that the uterus and ovaries are not required for the expression of PGF2alpha-induced nesting behaviour and the removal of the reproductive tract appears to have facilitated increased levels of gathering. This suggests that PGF2alpha induces luteolysis and nest building separately, and that PGF2alpha or a metabolite, may act centrally to mediate directly its effects on prepartum nest building in the pig.