[Health and fertility in relation to production. Embryonal mortality in swine: incidence and possibilities for prevention].

The embryonic mortality rate in the pig is 20-40%. Part of the variation in incidence is due to breed differences. Unavoidable chromosome mutations are unimportant as a cause of embryonic mortality. Within breeds, the incidence depends on factors such as the boar, the interval between parturition and conception, the time of insemination in relation to ovulation, and the level of feeding and stress during early pregnancy. If these factors are taken into consideration, the incidence of embryonic mortality can be reduced. The aetiology of a part of the embryonic mortality is still unknown, and it is thus difficult to predict whether this part can be prevented. In this context, however, recent publications on the relationship between variation in early embryonic development and embryonic mortality, and on the positive effect of the administration of exogenous steroids during early pregnancy on litter size, are promising.