Fertilization and embryo mortality in Bungaree Merino ewes mated in autumn

Abstract

Fertilization and embryo mortality were examined in Bungaree ewes to determine their contribution to the known low autumn fertility of these ewes. A group of approximately 100 ewes was joined for 34 days in April with two Bungaree rams and a similar group was joined with two Peppin rams. Ewes were removed from the groups within two days of mating and half the mated ewes were laparotomized to determine ovulation rate and percentage of ova fertilized. Remaining ewes were allowed to lamb and embryo mortality was calculated as the difference between the expected number of fertilized eggs and the number of lambs born to ewes mated but not laparotomized. There was no significant difference between the groups in either fertilization rate or estimated embryo mortality. The mean fertilization rate was 53.3 per cent of ova recovered (53.4 per cent of ewes had fertilized ova) and embryo mortality was calculated to be 19.6 per cent of ova fertilized. The mean percentage of ewes losing all fertilized ova was calculated to be 7.8 per cent of ewes mated. It is suggested that fertilization failure is the major factor in the low fertility of these ewes.