Puberty in bulls occurs when they can produce viable sperm. This happens at approximately 12 months of age, though it can vary in individual bulls several months before or after this age depending on biological type (primarily frame size and potential mature weight), nutrition, and health status. Most bulls have reached puberty when scrotal circumference measures approximately 26 cm. A generally accepted guideline is to purchase/use only yearling bulls that have a minimum 32-cm scrotal circumference. Bulls can remain in service until they are 10 or 12 years of age. However, this is not the norm and usually remain in the herd for 4 to 5 years. Many do not last nearly that long due to hoof problems, structural problems, fertility issues, or injuries.