Ovulatory activity, hormonal induction of ovulation and fertility of young Cashmere and Angora female goats in a temperate environment

Abstract

Reproductive parameters of young Cashmere and Angora goats born between 1988 and 1990 and grazed on temperate pastures in southern Australia were examined with a view to reducing the age of first breeding. Females born in August or October of 1989 and 1990 were examined each month by laparoscopy to determine natural ovulatory activity when 6-19-months old. Cashmeres commenced ovulating as young as 7 months of age or as light as 12 kg. Almost all Cashmeres were ovulating by 8-10 months of age at a liveweight of at least 18 kg, and their breeding season extended from April to October. By comparison with Cashmeres, Angoras grew more slowly, fewer ovulated, they commenced ovulation later, their ovulation rates were lower and their breeding season was shorter. A stratified sample of these females was injected with 200 I.U. or 400 I.U. of pregnant mare serum gonadotrophin (PMSG) after treatment with controlled internal drug release (CIDR) devices for 16-18 days to induce ovulation at 6, 9, 12, 15 and 19 months of age. Ovulation rates after CIDR-PMSG treatment were higher for Cashmeres than for Angoras and tended to be higher for females injected with 400 I.U. PMSG than 200 I.U. PMSG. The proportion of females remaining anovulatory after exogenous hormonal treatment was higher for Angoras than for Cashmeres (38% and 10% respectively) but it was not affected by the dose of PMSG or age. For kids born in 1989, the kidding rates to insemination (with follow-up mating) after CIDR-PMSG treatment for 8-month-old and 20-month-old Cashmeres (in the breeding season) were similar (75.0% and 83.8% respectively) but the rate for 14-month-old Cashmeres was only 10.0% (in the non-breeding period). The kidding rates for Angoras bred at 8, 14 and 20 months of age were 8.4%, 20.0% and 30.0% respectively. Ovulatory activity and fertility in the non-breeding period, with or without CIDR-PMSG treatment, did not improve with melatonin treatment.