Determining Reproductive Fertility in Herd Bulls

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Jordan Thomas, Assistant Professor, Animal Sciences

An important factor influencing the productivity of a beef cattle operation is the percentage of the calf crop weaned. This is determined by many factors, but certainly one is the number of cows bred during the breeding season. When natural service is used for breeding, the herd bull(s) will have more influence on herd fertility than any other single animal. Accordingly, loss of fertility by a bull can cause substantial loss to a potential calf crop.

Since the majority of beef cows in the United States are bred by natural service, it is important that bulls be managed to optimize breeding performance. Several factors influence a bull’s fertility. A bull must be adequately developed and have reached puberty in order to be an effective service sire. Additionally, several physical characteristics (soundness, scrotal circumference, semen quality, etc) and non-physical characteristics (libido and social dominance) affect the reproductive fertility of herd bulls.