Deprivation of straw bedding alters PGF(2alpha)-induced nesting behaviour in female pigs

Sows are highly motivated to build a maternal nest on the day preceding parturition. A model for nest building has been established in pigs, in which exogenously administered prostaglandin F(2alpha) (PGF(2alpha)) may be used to elicit nesting behaviour in cyclic, pseudopregnant and pregnant pigs. The aim of this experiment was to examine the effects of deprivation of straw bedding on PGF(2alpha)-induced nest building in pseudopregnant Large White gilts. Oestradiol valerate injections (5 mg/day) were given on days 11-15 of the oestrous cycle to induce pseudopregnancy. The pigs were housed individually in a pen (2.8x1.7 m) and provided with 2-kg fresh straw each day. On the test day, on day 46 or 47 of pseudopregnancy, half of the pigs were deprived of straw (substrate effect) and they were injected intramuscularly with saline or 15 mg of PGF(2alpha) (Lutalyse, Upjohn) (treatment effect) allocated in a Latin-square design. Behaviour was recorded onto video tapes for 1 h either side of treatment for analysis using a computerised event recorder. PGF(2alpha)-treated pigs housed in bare or strawed pens showed significantly higher frequencies of pawing and rooting, and stood for longer than saline-treated controls. This treatment effect has been previously shown to be comparable to pre-partum nest building. The removal of straw significantly reduced the frequency of pawing and the duration of rooting by PGF(2alpha)-treated pigs. The results demonstrate that nesting behaviour can be initiated by exogenously administered PGF(2alpha) and is further modified by the provision of straw. This suggests that PGF(2alpha)-induced nesting behaviour is subject to environmental feedback.