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A Study of the Inheritance of Breeding Efficiency in the Beltsville Dairy Herd¹

Department of Animal Husbandry, Cornell University, Ithaca, N. Y.

J. F. Sykes and R. C. Jones³

Bureau of Dairy Industry, U.S.D.A.

ABSTRACT

Conclusions: The results of this investigation indicate that the intraherd repeatability and heritability values of breeding efficiency in dairy cattle are low. When the number of services required for conception, the number of days from first service to conception, or the regularity of the occurrence of estrus are used as measures of breeding efficiency, selection for improvement in breeding efficiency will not be very effective. Dairy cattle breeders can make greater progress in the improvement of the genetic merit of their herds by practicing selection for other traits of economic importance, such as high milk production, which has much higher repeatability and heritability values.

Environmental factors that appear to be of relatively minor importance as the causes of variation in breeding performance are age of the cow, season of the year, and time trends. A large body of accurate and complete data, based on a herd where adequate controls are maintained purely for the purpose of investigating breeding performance, is needed in order to obtain a more exact picture of the relative importance of these environmental factors.

¹ These data were made available through a cooperative project between the University of Maryland and the Bureau of Dairy Industry and are taken from a thesis submitted by the senior author for the degree of Doctor of Philosophy in Animal Breeding at Cornell University.

² Present address—Animal Industry Department, North Carolina State College, Raleigh.

³ Presently consultant, International Programs, Agricultural Research Administration, U.S.D.A., Beltsville, Md.