Despite overwhelming evidence supporting the genetic advantage of artificial insemination over natural service, many dairy producers consider the use of natural service to be advantageous to their reproductive management program. Considering the low heat detection rates and pregnancy rates on many dairy farms today it is no wonder why bulls are being used more often. Natural service becomes a valid option when the pregnancy rate falls below 10%. This option will only be maximized if bulls are employed that are able and willing to impregnate cows in estrus. Bulls should pass a breeding soundness examination prior to use and this test should be repeated quarterly. Bulls should receive the same immunizations or vaccination program as the cows in the milking herd, except only bulls are given the trichomonosis vaccination. Particular attention should be made to the prevention of vibriosis and trichomonosis. Reproductive performance monitoring of natural service bulls should be conducted on a periodic basis. The use of the new DHI-PCDART report 126 can be used to monitor pregnancy rates and thus natural service versus AI breedings. Housing and dietary factors may impair bull fertility and management should be aware of and consider alternatives to maintain the highest fertility possible. An important aspect of bull management is the bull to cow ratio. Although superior bulls can accommodate considerably greater number of cows, the standard recommendations of 1:25 or 1:30 bull:cow ratio is generally safe, especially with young bulls. Social effects may strongly influence bull reproductive success. With multi-bull groups, bulls of higher rank may inhibit bulls lower in dominance rank. In general, social rank is most influenced by age, or seniority, although body size, presence of horns and breed may also be important. The most serious effects of adverse bull interactions may be avoided by employing homogenous groups of younger bulls. However, as older females may also inhibit inexperienced young bulls, it is wise to monitor breeding activity, at least initially. Safety is a major concern with bulls on dairy farms, partly because cows are handled often and the lack of adequate facilities and personnel training for bull handling. Bad temperament in a dairy bull should not be tolerated. Other safety considerations should include the preferred use of younger bulls and strict adherence to safety protocols. Accidents occur when people cut corners with such protocols, particularly when they assume they are safe. Bulls become more agitated and dangerous when separated. It is advisable to keep them in groups as much as possible.

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