Pharmacological Evidence that Prolactin Acts from Late Gestation to Promote Maternal Behaviour in Rabbits

We investigated the role of prolactin and suckling stimulation in the expression of maternal behaviour of primiparous rabbits. Bromocriptine (1 mg/kg/day), given to intact mothers across postpartum days 1-5, decreased serum concentrations of prolactin to undetectable levels, reduced crouching, and increased time inside the nest. Failure of maternal nest-building, provoked by bromocriptine injections from pregnancy day 26 to parturition or to postpartum day 5, correlated with a stronger reduction in crouching and an increased time inside the nest, measures of disturbed maternal behaviour, on postpartum days 3 and 5. Preventing suckling by thelectomy did not prevent prolactin release but reduced crouching incidence and increased the time spent inside the nest on postpartum days 3 and 5. Bromocriptine, injected in thelectomized mothers across postpartum days 1-5, further reduced the incidence of crouching and increased the time spent inside the nest on postpartum days 3 and 5. We conclude that prolactin acting prepartum facilitates maternal behaviour initiation in rabbits and, together with pup stimulation, maintains this behaviour across lactation.