Induction of ovulation in seasonally anoestrous ewes by continuous infusion of low doses of Gn-RH

Abstract

Two groups of 12 seasonally anoestrous ewes were infused with Gn-RH at the rate of 125 or 250 ng/hr for 48 hr. Four control ewes were infused with the saline vehicle alone. Mean LH concentrations increased significantly in response to Gn-RH infusion and were significantly higher (P < 0.05) in ewes receiving 250 ng Gn-RH/hr. LH concentrations remained unchanged in the control ewes. Oestrus was detected in 22/24 Gn-RH-treated ewes and occurred at a mean time of 37.0 ± 1.2 hr after the start of infusion. Ovulation occurred in all but one of the 24 Gn-RH-treated ewes with mean ovulation rates of 1.27 ± 0.14 (125 ng-Gn-RH/hr) and 1.75 ± 0.22 (250 ng Gn-RH/hr). These results demonstrate that a sustained elevation in mean circulating concentrations of LH induced by continuous administration of Gn-RH is sufficient to invoke the final phases of follicular development, and thereby ovulation, in the seasonally anoestrous ewe.