Breeding Soundness of Bulls

for half the genetic material in only one calf each year, while the bull is responsible for half the genetic material in 20 to 50 calves. The bull’s ability to locate cows in estrus and breed them is clearly vital to a successful breeding program. Bulls differ in physical appearance, fertility and sex drive (libido). In the past, when a cow failed to become pregnant it was assumed that she was at fault. Occasionally, that is true. However, a clear understanding of the male reproductive system and the differences between reproductive capabilities of bulls indicates that the cow is not always at fault.