This decision should largely be based on the geographic location of the herd and the classification of the herd as a closed, modified open or open herd. Closed herds have no new additions except for bulls and there is no animal to animal contact with neighboring herds. New bulls should be isolated, tested and vaccinated for transmissible diseases before introduction into the herd. Level of immunization for a closed herd is less because risk of exposure is low. Modified open herds have a higher risk of exposure to pregnancy-wasting diseases through additions of bulls and replacement heifers, animals moving in and out of the herd to exhibitions, or through contact with neighboring herds.
Open herds have a very high risk.
This exposure is due to the frequent introduction of replacements or exposure of the breeding herd to stocker cattle or other recently purchased, stressed cattle. Like human employees, you want your bulls to clock in for work every day they are called upon. To be sure they don't have any unwanted sick days, proper nutrition, immunization, housing, parasite control and a functional reproductive tract are required. Good managers watch over and evaluate their employees' progress. Neglecting herd sires can lead to unacceptable performance, reduced calf crop, younger calves at weaning and decreased income.