A Study of the Inheritance of Breeding Efficiency in the Beltsville Dairy Herd

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Abstract
Environmental factors affecting the reproductive preformance of cows in the dairy herds maintained by the Bureau of Dairy Industry, Beltsville, Md., were studied, and unbiased estimates of the repeatability and heritability of breeding efficiency in these herds were obtained. Data, available on 834 cows, covered the period from 1920 through 1950. Estimates of the variance components were obtained by a method adapted to obtaining unbiased estimates in nonorthogonal data. Three measures of breeding efficiency were studied. Repeatability was estimated to be 0.18 from the data on the regularity of the occurrence of estrus, 0.12 from the data on the number of services required for conception, and 0.11 from the data on the number of days from first service to conception. Heritability values obtained, using the same measures of breeding performance, were 0.05, 0.07, and 0.07, respectively. Environmental factors found to be of minor importance as the causes of variation in breeding performance were age of the cow, season of the year, and time trends. Advantages and limitations of the data are discussed.