Maternal acceptance of alien lambs in ewes treated and untreated with oestrogen at birth

Abstract

Sixteen ewes suckling their own lambs and 20 ewes from which lambs had been removed at birth were tested on 7 occasions, between 1 and 48 h postpartum, for their maternal interest in their own lamb, an alien lamb of similar age, a newborn alien, a ewe-fed older alien and an artificially fed older alien. Half of the ewes under each treatment were given 20 mg 17β-oestradiol benzoate, intramuscularly just prior to parturition, plus 5 mg 17β-oestradiol intravenously at the same time and at 2, 4 and 6 h postpartum. Oestrogen treatment of ewes whose lambs had been removed at birth, produced a small but significant improvement in the number of acceptances of own lambs and alien lambs of similar age and treatment. There were small non-significant trends in the same directions with the other 3 classes of lamb in both groups of ewes. It appears that oestrogen treatment of parturient ewes has only marginal effects on maternal interest and would be of little value in facilitating fostering. Ewes kept from their own lambs accepted alien lambs much more frequently than did ewes left with their own lambs. Hence, limited exposure of newly lambed ewes to lambs may be useful in facilitating fostering by sustaining maternal receptivity but delaying discrimination between lambs. Artificially fed alien lambs, kept from ewes except at testing, were more frequently accepted than alien lambs of a similar age kept with their dams. Thus maternal recognition of lambs as aliens may be facilitated by maternal labelling, and fostering is more likely to be successful if the foster lamb has been isolated and artificially fed, than if left with its dam.