Fertilization and early embryonic losses in ewes that had grazed oestrogenic pastures for 6 years

Abstract

Ewes that had grazed native, improved, or red clover pastures over 6 years were slaughtered 1–2 days, 30 days, or 60 days post coitum (pc.). Their reproductive tracts were examined for the distribution of spermatozoa, for the presence of fertilized eggs or embryos, and for cystic endometrial hyperplasia (C.E.). The severity of the C.E. was significantly greater in ewes grazed on red clover (P < 0.02), but there was no significant difference between the ewes that had grazed the native or the improved pastures. Fewer of the ewes with > 10 cysts in the cervix had sperm in the fallopian tubes, as compared with ewes that had < 10 cysts (P < 0.005). Of the ewes with > 10 cysts in the cervix, or in the uterus, a smaller proportion were pregnant 30 days p.c. than in ewes with < 10 cysts (P < 0.005). Increasing the number of services per ewe resulted in an increased proportion of ewes in which sperm were found in the tubes, and in an increased proportion of the eggs being fertilized. The major cause of the infertility in ewes that have grazed oestrogenic pastures over long periods appears to be non-fertilization due to absence of sperm from the fallopian tubes. Death of embryos in the first 60 days p.c. also appears to contribute to the low fertility in ewes with C.E.