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

The onset of maternal behaviour in sheep is controlled by levels of oestrogen and progesterone in gestation and the release of oxytocin during delivery. Factor analysis was used to investigate the relationships between maternal behaviour, offspring behaviour, and maternal ovarian hormone levels during gestation in sheep. Ewes gave birth to lambs following embryo transfer between two breeds (Suffolk and Scottish Blackface), which differ in their expression of maternal behaviour. Plasma oestradiol-17 beta concentration was significantly higher in Blackface ewes in the last 6 weeks of pregnancy, whereas plasma progesterone was higher in Suffolk ewes in early and mid gestation. Factor analysis revealed three factors that accounted for 50% of the total variation between variables. Factor 1 described lamb activity and had positive loadings for lamb behavioural latencies immediately postpartum, and negative loadings for sucking frequency. Factor 2 described some aspects of ewe maternal behaviour, and had positive loadings for ewe-lamb separation and lamb vocalisation, and negative loadings for ewe grooming behaviour and plasma oestradiol concentration. Factor 3 described ewe and lamb-sucking interactions, and had positive loadings for ewe moving as the lamb made sucking attempts, and negative loadings for ewe and lamb vocalisation. Factor 1 scores were significantly affected by lamb breed: Suffolk lambs received positive scores, indicating a longer latency to right and stand, whereas Blackface lambs had negative scores. Maternal progesterone concentration was significantly correlated with Factor 1 scores. Factor 2 and 3 scores were significantly affected by ewe breed. This study has shown that there are two behavioural axes to maternal behaviour in sheep, and that maternal oestradiol concentration is related to affiliative behaviours (e.g., grooming) but only weakly to ewe responsiveness to lamb-sucking attempts. (C) 1999 Elsevier Science Inc.