What is the minimum age for bulls before they can be used for service?

Bulls typically reach sexual maturity and are able to successfully breed at around 12 to 15 months of age; however, they are recommended for service at a later age to ensure they are fully developed both physically and reproductively. The common consensus in the livestock industry is that bulls should be at least 18 months old before they are used for service.

Using bulls that are too young may lead to suboptimal breeding outcomes and could affect the overall health and development of both the bull and the cattle being bred to him. As such, the benchmark for best practices in breeding dictates a minimum of 18 months for bulls, allowing them to be more effective and healthier contributors to the breeding program. This understanding indicates that the age mentioned in the question is meant to represent best practices in animal husbandry.