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G. R. FALLON

Summary.

Rectal temperatures of 934 Jersey and Australian Illawarra Shorthorn dairy cows were recorded during summer months immediately before artificial insemination. They ranged from 98·8°F to 105·0°F (mean 101·6 ± 0·9°F) and were related directly to stage of oestrus, supporting an earlier report of a thermal response at oestrus. Thus, the temperature of the cow's genitalia may be high during oestrus; and the sperms may be subjected to such environment for several hours after insemination.

In addition, the data support the hypothesis that the normal diurnal rhythm of body temperature is restored some hours before ovulation occurs. Under such conditions, high rectal temperatures at the time of insemination were not inimical to the subsequent fertilization process. Indeed, in one group of cows, inseminated at a late stage of oestrus, fertility was better (P <0·05) in cows with elevated temperatures than in those with low values.

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G. C. ASHTON and G. R. FALLON

Summary.

It has been reported previously that serum β-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 β-globulin locus in cattle affects fertility in two ways, at fertilization, and in utero.