The effect of bromocryptine on plasma prolactin concentration and ovulation rate in ewe breeds with different fecundity rates

Abstract

The objective of the study was to investigate the effect of bromocryptine on the neuro endocrine feedback mechanisms that control ovulation rate in two sheep breeds with different fecundity and ovulation rates (Scottish Black Face and Finnish Landrace). Bromocryptine was administered i.m. in doses of 1 mg at 12-h intervals for an entire estrous cycle (16.0 ± 0.5 days), to 12 Scottihs Black Face and 12 Finnish Landrace ewes. The aim was to record the blood prolactin levels and the effect of bromocryptine on ovulation rate. The experiment was carried out during the breeding season (November 1999) and repeated in January 2000. In the first study the ovulation rate was not affected by the low plasma prolactin (<0.5 ng/ml) levels induced by the drug. Ovulation rate in the Finnish Landrace was 2.85 ± 0.69 CLs/ewe for the control and 2.42 ± 0.53 CLs/ewe in the treated group. In the Scottish Black Face ewes, ovulation rate was 1.12 ± 0.35 and 1.37 ± 0.51 CLs/ewe for the control and treated ewes, respectively. When the experiment was repeated at the end of breeding season in January 2000, the ovulation rates were similar. It was concluded that the administration of bromocryptine during an entire estrous cycle at the beginning and the end of the mating season did not affect fecundity and ovulation rate in ewes with different prolificacies.