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This NebGuide describes factors to consider when evaluating a beef bull's reproductive ability. These include the reproductive tract, semen and mating desire. A herd bull that will settle a higher percentage of cows during a limited breeding season is essential to a successful cow-calf operation. In many cow-calf operations, however, the bull's role in the herd's reproductive performance is taken for granted. The bull's fertility is several times more important than that of a cow. Each bull can be expected to settle as many as 30 cows. The bull also contributes half of the genetic potential of the entire calf crop, while each cow is expected to wean only one calf each year. Sub-fertile bulls frequently cause low calf crop percentages; they also may be the reason for poor herd weaning weights. Every cycle that a female fails to conceive can cause a 35 to 45 pound loss in calf weaning weights. Poor fertility or infertility in bulls can be expensive to the cow-calf producer. Research has shown that about 20 percent of all beef bulls are deficient in some aspect of reproductive capacity. The reproductive function of bulls depends upon sexual desire, mating ability, and the formation and deposition of semen. Determining the condition of all body systems that affect reproduction is as important as determining the status of the genital system. Performance records and pedigrees are important, but the sires must be capable of settling cows.