Fertilization, sperm transport, and early embryonic loss in ewes grazed on cultivars of subterranean clover. (T. subterraneum)

Abstract

The causes of infertility due to phyto-oestrogens were investigated in ewes which had grazed Dwalganup, Yarloop, Geraldton, Woogenellup, and Mount Barker cultivars of subterranean clover (T. subterraneum L.) for 5 years. At laparotomy, sperm transport was investigated by making counts of spermatozoa in the oviduct 22-26 hr post coitum; fertilization rates were checked 72 hr post coitum and embryonic survival at 27-31 days. A larger proportion of ewes on high oestrogen cultivars Dwalganup, Yarloop, and Geraldton) had low oviducal spermatozoa counts and the fertilization rate was significantly lower (P < 0.05) than in ewes grazed on low oestrogen cultivars (Woogenellup and Mount Barker) (44% v. 63 %). There was no statistically significant difference in embryonic survival between these groups. Merino ewes had fewer oviducal spermatozoa and a lower (P < 0.05) fertilization rate than Border Leicester x Merino ewes. Impaired sperm transport is considered to be the reason for reproductive failure in the ewes that had grazed the high oestrogen cultivars of subterranean clover.