Effects of growth hormone injections on ovulation rate in ewes

Coopworth ewes were either treated with 5 mg recombinant-derived bovine growth hormone per day for each day of the oestrous cycle or were untreated. Ovulation rates at the pre-treatment, post-treatment and a subsequent oestrus were determined by endoscopy. These were 1.34, 1.51, 1.38 for the treated ewes and 1.32, 1.43, 1.39 for the control ewes. The ovulation rate post-treatment was significantly higher than for the other two cycles in the treated ewes but it was not significantly different from the post-treatment value of the control ewes. Plasma concentrations of insulin-like growth factor-I (IGF-I) were elevated during treatment (90-130 nmol L-1) compared with concentrations of 25-50 nmol L-1 in the control ewes. No relationship was found between plasma IGF-I concentration and ovulation rate. Injection of ewes grazing ryegrass/white clover pasture with bovine growth hormone did not result in increased ovulation rate.