Attraction and repulsion by amniotic fluids and their olfactory control in the ewe around parturition.

The reaction of ewes towards amniotic fluids was studied in intact multiparous ewes in various physiological states (oestrus, luteal phase, mid-pregnancy and around parturition), using a test of preference for food associated or not with the presence of amniotic fluids in the food. Fluids were collected on alien newborn lambs. Results indicate that ewes are strongly repelled by amniotic fluid at all of the times tested except for a short period around parturition. Immediately before expulsion of the foetus ewes become strongly attracted by amniotic fluids. This attraction persists just after parturition, but fades within 4 hours in most animals. This attraction-repulsion behavior appears to rely heavily on olfactory cues. Ewes made anosmic with zinc sulphate do not show repulsion or attraction towards amniotic fluids at any of the physiological states studied. These results are discussed in the light of our knowledge about the factors controlling the onset of maternal behavior in the ewe (hormones and genital stimulation).