Divergent selection for ovulation rate in sheep : effect on embryo survival

Extract

The relative importance of genetic variation in ovulation rate and in embryo survival together with the genetic relationship between these traits are important issues in terms of manipulating prolificacy in all multitocous mammalian species. Evidence in sheep, primarily from study of breed differences but also based on results of selection for litter size, shows that genetic variation in litter size is essentially attributable to differences in ovulation rate although genetic differences in embryo survival have been identified. Results from selection on litter size also suggest that genetic variation in ovulation rate is independent of any variation in embryo survival. The evaluation of the relationship between these traits in sheep is somewhat problematical in most populations due to the low level of ovulation and particularly the associated high proportion of ewes which shed a single ovum. The objective of the present study was to use lines of Finn Sheep, a breed with a high ovulation rate and in which single ovulations are rare, which have been developed by divergent selection on ovulation rate to evaluate the genetic association between ovulation rate and embryo survival.