Effects of lambing induction on the sensitive period for the establishment of maternal behaviour in sheep

The existence and length of the sensitive period for the establishment of maternal behaviour was investigated in aged, thus presumably multiparous, merino ewes as well as the possible effects of inducing parturition on this component of maternal behaviour. While a few dams still showed spontaneous maternal behaviour after a 24 hr mother-young separation starting at parturition, maternal responsiveness had faded in most cases after 4 to 12 hr of such a separation. When realized two to four days after lambing, a 24 hr separation was of little consequence on maternal behaviour. Ewes which eventually accepted their lambs, either spontaneously or after human intervention, all established a discriminative behaviour at suckling. Inducing parturition by an IM injection of 15 mg of dexamethasone did not affect the length of the sensitive period. By constrast inducing lambing with 20 mg of oestradiol benzoate IM resulted in a significant lengthening of the sensitive period. Possible roles of oestrogens and prolactin are discussed in this respect.