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

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Abstract
Conception rate from 1st 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 heifers was affected significantly by 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 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 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.