A population study of apparent embryonic mortality in cattle, with special reference to genetic factors

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Abstract
SUMMARY: Apparent mortality among 280 215 embryos from the 4th to 16th week of gestation was studied from returns to service records following first inseminations with fresh semen from 100 bulls of five dairy and three beef breeds of cattle over a period of 8 years.The average incidence of apparent mortality was 20·3% for embryos conceived by fresh semen first inseminations. Differences in rates of apparent embryonic mortality between breeds of sire and also between sires within the Guernsey, Ayrshire and Dairy Shorthorn were statistically significant although confounded with the breed of dam. The highest incidence was from matings by bulls of the Channel Island breeds. These results suggest that hereditary factors influenced embryonic mortality in cattle.The rate of apparent mortality was higher among embryos conceived by frozen semen than by fresh semen. Ageing of fresh semen extra-corporeally also increased the rate of apparent embryonic mortality but to a lesser extent than frozen semen.The rate of apparent embryonic mortality increased with the greater number of inseminations required for conception possibly because of a deteriorating maternal environment.