-GLOBULIN TYPE, FERTILITY AND EMBRYONIC MORTALITY IN CATTLE

Abstract

It has been reported previously that serum [beta]-globulin polymorphism affects fertility in dairy cattle, matings between homozygotes being significantly more fertile than matings involving heterozygotes. Indirect methods have been used to determine whether this is due to differential mortality of the embryonic genotypes, or to differences in fertilization efficiency. From a study of six unrelated dairy-cattle populations and a closed beef-cattle population, it was shown that an excess of heterozygotes is born. The distribution of returns 25 days or longer after artificial insemination, used as an index of embryonic death, as well as the distribution of genotypes from known matings, support the conclusion that homozygotes are less viable than heterozygotes in utero. The distribution of returns 0 to 24 days after insemination, however, showed that matings between homozygous parents of like genotype have a greater chance of achieving fertilization than matings between homozygous parents of unlike genotype. It is concluded that the [beta]-globulin locus in cattle affects fertility in two ways, at fertilization, and in utero.