Impact of Overuse and Sexually Transmitted Infections on Seminal Parameters of Extensively Managed Bulls

Abstract

Natural service is currently the predominant method of breeding in extensively managed beef herds. In these herds, the importance of the bull has been largely overlooked, focusing instead on female fertility. However, the bull might be the most important factor in determining the reproductive performance of the herd, because one subfertile or infertile bull could mean a decrease of 25 to 40 calves per year. Thus, bull management is critical to increase herd fertility. Infectious bovine rhinotracheitis (IBR) and bovine viral diarrhea (BVD) are infections associated with reduced conception rates. In this study, we analyzed the effect of IBR, BVD, and bull: cow ratio on seminal parameters of the bull and herd fertility, finding a significant negative effect of BVD on sperm concentration and motility, and a negative correlation between the number of cows per bull and herd fertility. Our data suggest that serological control of BVD and sperm parameters, as well as including less than 40 cows per bull, could improve the reproductive efficiency of the herd in extensively managed herds.