Factors Associated with the Duration of Gestation in Dairy Cattle

Abstract

The duration of gestation in dairy cows is of importance to the dairy husbandman from a management standpoint, for it is desirable that dairy cows be in a no~l-lactating state during the last 6 to 8 wk. of each pregnancy. Thus, it is possible to prepare the cow physically for parturition and her next lactation. Dairy cattle breed associations also require that a living calf be produced within a maximum time limit after the completion of certain types of official production records. The purpose of this requirement is to assist in verifying the duration of pregnancy during the Official testing period. Recently the Brown Swiss Cattle Breeders' Association has extended the calving requirements following the completion of an official record to conform with the abnormally long gestation period found to exist in the Brown Swiss breed. Likewise, the Holstein-Friesian Association has reduced the gestation length used in the verification of applications for registration. This decision was based on the preliminary results of this study and data from similar investigations. In addition to these very practical applications, the possibility of various environmental and genetic factors influencing the duration of gestation is intriguing and may lead to fundamentally important discoveries.