Parity effects on maternal behaviour are not related to circulating oestradiol concentrations in two breeds of sheep

Primiparous females of many species, including the sheep, do not show as competent maternal behaviour as multiparous mothers. In this study we investigated whether circulating concentrations of oestradiol might be related to this response, since breed differences in oestradiol concentrations have been shown to correlate with maternal behaviours. Oestradiol concentrations were measured in plasma collected at 2-weekly intervals from primiparous and multiparous ewes of two breeds (Scottish Blackface and Suffolk) throughout gestation, and maternal behaviour was recorded at parturition. Circulating oestradiol concentrations, and the ratio of oestradiol to progesterone concentration (O:P ratio) were higher in late pregnancy in Blackface ewes, but there were no significant effects of ewe parity. However, there was a significant interaction between breed and parity as O:P ratio was lower in primiparous Suffolk ewes compared to multiparous. This relationship was not seen in Blackface ewes. Blackface ewes of both parities groomed their lambs more frequently and made more low-pitched vocalisations than Suffolk ewes. Primiparous ewes were more likely to move as the lamb attempted to suck, and to show withdrawal or aggression towards the lamb. Primiparous Suffolk ewes also made more high pitched bleats than other classes of ewe. The data support previous studies which show an effect of breed on circulating oestradiol and O:P ratio but suggest that parity effects on maternal behaviour may be mediated by sensitivity to circulating concentration of oestradiol rather than variations in the plasma concentrations of this hormone.