Exogenous prolactin delays photo-induced sexual maturity and supresses ovariectomy-induced luteinizing hormone secretion in the turkey (Meleagris gallopavo)

Abstract

A direct effect of prolactin (Prl) on gonadotropin secretion has been suggested but not convincingly demonstrated. The secretion of LH in response to photostimulation (phs) and ovariectomy (ovx) was evaluated in adult female turkeys that had received injections of ovine Prl (124 IU/bird/day for 14 days). In experiment 1, oPrl administration initiated on the day of ovx and phs in reproductively quiescent birds suppressed (p < 0.05) the elevated LH from a peak level of 11.7 ± 3.5 ng/ml to 5.1 ± 0.8 ng/ml in ovx hens. The photo-induced LH increase was unaffected by the oPrl treatment in intact birds. In experiment 2, the oPrl treatment was initiated 7 days before ovx and/or phs. This treatment blunted the peak increase in LH level that follows phs in intact (p < 0.05) and in ovx (p < 0.05) hens. In both experiments, onset of lay following phs was delayed (p < 0.05) in the oPrl-treated groups (29.4 ± 0.9 days vs. 22.3 ± 0.9 days; 34.8 ± 0.5 days vs. 25.0 ± 0.9 days). In experiment 3, administration of oPrl after ovx of laying hens suppressed the LH rise at essentially all sampling times tested. At the end of the experimental period, 6 of the 7 sham-operated, oPrl-treated laying hens, but none of the sham controls, displayed incubation behavior and had Prl levels of 1020 ± 370 ng/ml compared to 34 ± 7 ng ml in vehicle-treated controls. The results suggest a role for Prl in incubation behavior and LH secretion in the turkey.