Genetic Variation in Services Per Conception and Calving Interval in Dairy Cattle

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Abstract
Number of services per conception and the length of the interval between calvings were studied to determine the genetic variance in these commonly used measures of reproductive efficiency. The data included 1129 cows with services per conception for 2443 calvings and 1016 cows with 2419 calving intervals. The mean number of services per conception was 1.80 and the mean calving interval was 406 days. The estimate of heritability of services per conception was 0.026, while the intra-cow repeatability was zero. Heritability of calving interval length was zero; although, repeatability was 0.133. Evidence from this study indicates little existing genetic variability in the two measures of reproductive efficiency studied. The number of services required for conception for one calving is of no value in predicting the number of services that will be required for a subsequent pregnancy. The length of calving interval does appear to be slightly more a characteristic of the individual cow than is services per conception. Application of genetic principles in selection for fewer services per conception or for a shortening of the length of calving interval has little to offer the dairy cattle breeder. Copyright © . .