RELATIONSHIP OF CIRCULATING ESTROGEN AND PROGESTERONE CONCENTRATIONS DURING LATE PREGNANCY AND THE ONSET PHASE OF MATERNAL-BEHAVIOR IN THE EWE

Maternal behavior in several species has been stimulated with exogenous estrogen and this behavior can be blocked with progesterone (P4). In this study, attempts are made to correlate the ewe's endogenous pattern and concentration of these two steroid hormones during late gestation with specific maternal behaviors. Five yearling ewes with known breeding dates were fully acclimated to the presence of the investigator during the gestation period. Each ewe was allowed to parturiate in the location of her choice within the small barn and paddock in which she had been housed throughout gestation, and specific maternal behaviors were recorded. All areas of the facility were equally observable to the investigator. Blood was collected daily at 16:00 h via jugular venipuncture from 21 days prior to the expected lambing date until the day of parturition. Estrogen (estrone + estradiol-17-beta; E) and P4 were measured in plasma by radioimmunoassay. High correlations were observed between E concentrations 2-3 days prepartum and maternal behaviors displayed by the ewe during the first 4 h postpartum. Specific maternal behaviors and correlations are: (1) time from the completion of birth to the start of grooming (r = -0.97); (2) percentage of suckling attempts accepted by the ewe (r = 0.99); (3) mean number of vocalizations per min by the ewe (r = -0.96); (4) percentage of time of direct contact between ewe and lamb (r = 0.95). High positive correlations were also observed between P4 concentrations on the day of parturition and the time from the completion of birth to the start of grooming (r = 0.97), as well as the mean number of vocalizations per min by the ewe (r = 0.99). These data suggest that E exposure 2-3 days prepartum facilitates maternal behavior during the immediate postpartum period whereas P4 exposure inhibits such behavior.