The cells that produce sperm multiply and grow, thereby accounting for most of the increase of testicle size from birth to maturity. You can estimate the size of the testicles by measuring the circumference of the scrotum. A bull with a larger scrotal circumference also has half-sisters and daughters that reach puberty earlier. Proceedings of the Beef Improvement Federation. After a bull passes the BSE, he must be able to seek out and mate with the females in heat.
Bulls rely heavily on visual indicators to find females in heat.
When the bull sees females standing to be ridden, he will move into the group. The females that are standing to be ridden are the ones that will be served by the bull. The bull must also have sound feet and legs to transport himself freely and without stress. A bull with sore feet or hocks may move around to graze but refuse to mate because of the pain. Libido varies greatly between bulls and is not necessarily related to scrotal size, semen quality, growth rate or even social order.