Physiological correlates of maternal-offspring behaviour in sheep: A factor analysis

The onset of maternal behaviour in sheep is controlled by levels of oestrog en and progesterone in gestation and the release of oxytocin during deliver y. Factor analysis was used to investigate the relationships between matern al behaviour, offspring behaviour, and maternal ovarian hormone levels duri ng gestation in sheep. Ewes gave birth to lambs following embryo transfer b etween two breeds (Suffolk and Scottish Blackface), which differ in their e xpression of maternal behaviour. Plasma oestradiol-17 beta concentration wa s significantly higher in Blackface ewes in the last 6 weeks of pregnancy, whereas plasma progesterone was higher in Suffolk ewes in early and mid ges tation. Factor analysis revealed three factors that accounted for 50% of th e total variation between variables. Factor 1 described lamb activity and h ad positive loadings for lamb behavioural latencies immediately postpartum, and negative loadings for sucking frequency. Factor 2 described some aspec ts of ewe maternal behaviour, and had positive loadings for ewe-lamb separa tion and lamb vocalisation, and negative loadings for ewe grooming behaviou r and plasma oestradiol concentration. Factor 3 described ewe and lamb-suck ing interactions, and had positive loadings for ewe moving as the lamb made sucking attempts, and negative loadings for ewe and lamb vocalisation. Fac tor 1 scores were significantly affected by lamb breed: Suffolk lambs recei ved positive scores, indicating a longer latency to right and stand, wherea s Blackface lambs had negative scores. Maternal progesterone concentration was significantly correlated with Factor 1 scores. Factor 2 and 3 scores we re significantly affected by ewe breed. This study has shown that there are two behavioural axes to maternal behaviour in sheep, and that maternal oes tradiol concentration is related to affiliative behaviours (e.g., grooming) but only weakly to ewe responsiveness to lamb-sucking attempts. (C) 1999 E lsevier Science Inc.