Nonreturn Rate of Artificially Inseminated Dairy Cows as Affected by Age of Semen, Breed of Bull, and Season

Abstract

Summary Records from 71,098 first services involving 60 bulls from six dairy breeds were obtained during 1951 and 1953. The breed of bull, age of semen, date of service, and collection number were recorded in the field on IBM mark-sense cards. Records of repeat services included the code number of the bull previously used, and the collection number, so that unsuccessful first services could be identified. It was found that: (a) Nonreturn rate decreases from five to 11 percentage units (depending on breed) for each additional day of storage of the semen. (b) Breeds, as represented in this study, have different potential nonreturn rates, and these rates are differentially affected by storage of the semen. (c) Seasonal effects on the percentage of nonreturns depend, somewhat erratically, upon the age of the semen. (d) Although the decline in fertility of stored semen is least rapid in the winter months of December, January, and February—as might be expected—it is no greater in the summer than in the spring and fall seasons. However, it may be that apparent seasonal effects are partially confounded with dairy husbandry practices associated with recommended time between calving and first service, milk pricing systems, and types of milk marketing.