Heritability of Fertility in Dairy Cattle

Abstract

Low reproductive efficiency of dairy cattle has long been recognized as a cause of serious economic loss to the dairy farmer, and it lias seemed reasonable to assume that improvement in reproductive efficiency could be attained by selecting for some measure of this trait. If dairy cattle breeders are to select for high fertility measured in some particular manner--in addition to selecting for other traits of economic importance--it is important to know how effective selection for that particular measure of fertility can be, what the best selection procedure is, and what relative emphasis should be placed on fertility and other traits of economic importance. In order to answer such questions, it is necessary to have reliable estimates of the repeatability and heritability of the particular measure of reproductive efficiency which is to be used. In recent years a considerable amount of work has been done on this problem, and the measures of fertility most frequently employed have been the number of services required for conception, nonreturns to first service--which is undoubtedly highly correlated with the former--and in some instances, calving interval.