A Study of the Reproductive Performance of a Purebred Hereford Herd1

Abstract

The reproductive performance of a purebred Hereford herd was studied for the period from 1935 through 1952. The reproductive performance of this herd gradually declined during this period. The average reproductive performance for this period was: number of services per conception, 1.7; interval from calving to conception, 108.2 days; gestation length, 285.7 days; calving interval, 394.2 days; interval from calving to first breeding, 75.5 days; and interval from first breeding to conception, 31.0 days. In general, the reproductive performance was higher in summer and fall than in spring and winter. Cows more than 10 years of age declined rapidly in performance. All correlations and regressions of performance on age of cow were positive and significant. The rapid decline at the older ages caused the regression to be curvilinear. During the period of this study 530 cows were taken from the herd at an average age of 7.8 years. Cows that were sent to market at the end of their productive life had an average age of 9.2 years. Thus they had a productive life of 7.5 years. Heritability estimates of reproductive performance were determined by the paternal half-sib intra-class correlation, the correlation between daughter and dam records, and the regression of daughters' records on dams' records. The repeatability estimates were determined by intra-class correlations. The estimates were generally low. Most heritability estimates were near zero. Repeatability estimates varied from 0.03 to 0.15. Cows bred more than 60 days post partum required fewer services per conception than those bred prior to 60 days post partum.