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Genetic Factoes Affecting Conception Rate and Early Pregnancy Loss in Holstein Cattle¹

Departments of Genetics and Dairy Husbandry, University of Wisconsin, and Dairy Cattle Research Branch, USDA, Madison

ABSTRACT

Conception rate from first insemination and pregnancy loss to 152 days post-insemination were studied in 181 heifers and 346 parous cows. The effect of the sire line of the dam and system of mating of the embryo were studied in both groups and, in addition, the effect of season of birth on their conception rate was studied in the heifers. Adjustments were made to remove any effect of season of previous calving and parity on conception rate in the cows. Conception rate in the heifers was affected significantly by the season of birth and the interaction of sire line with the system of mating (P<0.05). In the cows, conception rate was affected significantly by the sire line (P<0.01) and the interaction of sire line with the system of mating (P<0.05). The over-all adjusted conception rate in the heifers was 63.6% as compared to 55.3% in the parous cows.

Pregnancy loss was not affected significantly (P>0.05) by either sire line or system of mating in the heifers, but the latter had a significant effect (P<0.05) on pregnancy loss in the cows. Higher conception rates were found in the systems of mating in which the potential embryo was outbred than those in which the potential embryo was inbred; whereas, pregnancy loss was greater in the systems of mating in which the dam was inbred than those in which the dam was outbred. This was true in both heifers and cows where the over-all losses were 2.5% in the heifers as compared to 13.0% in the cows.

¹ From the Department of Genetics (Paper No. 807) and Department of Dairy Husbandry; published with the approval of the director of the Agricultural Experiment Station. This study was supported in part by a grant from the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation and by a grant from the Emmons Blaine, Jr. Fund. Contribution from the Wisconsin Agricultural Experiment Station as a collaborator under the North Central Region Cooperative Research Project entitled Improvement of Dairy Cattle Through Breeding—NC-2, conducted in cooperation with the Dairy Cattle Research Branch, USDA.

² Agent of the Dairy Cattle Research Branch, USDA.

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