THE MERCK VETERINARY MANUAL
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Bull Reproductive Management

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A desirable goal for beef producers is a 95% calf crop delivered within 45–65 days, with an optimal weaning weight obtained at the most efficient cost. Bull selection, management, and evaluation of performance are integral aspects of beef improvement. The bull can affect calving percentage as well as quality of calves. The use of performance-tested bulls (beef and dairy) is recommended for both natural breeding and artificial insemination.

A disease control program for bulls should include the following procedures: 1) Before use, bulls should be checked for brucellosis, tuberculosis, trichomoniasis, and paratuberculosis (ie, from a herd free of paratuberculosis). Bulls previously used in other herds, particularly herds in which disease status is not known, may spread diseases, particularly campylobacteriosis and trichomoniasis. Prophylactic sheathwashing with antibiotics may reduce the risk of Campylobacter transmission. 2) Depending on prevailing health status and market requirements, bulls should be vaccinated against infectious bovine rhinotracheitis, bovine viral diarrhea, clostridia, Haemophilus, campylobacteriosis, and leptospirosis if available. Vaccines should be administered around puberty, at 6 mo and 1 yr of age, and then annually, 1 mo before the breeding season. 3) Breeding soundness examinations should be performed annually at the most economically advantageous time for the producer (usually 1 mo before the breeding season).

All bulls should be on the premises 2 mo before the breeding season to allow them to adapt to the environment. Isolation of all new additions to the herd (bulls or cows) is recommended for proper adaptation and preparation. A breeding soundness examination consisting of a thorough physical examination, including internal and external genitalia, measurement of scrotal circumference, and microscopic examination of semen for sperm motility and morphology, should be conducted ~1 mo before the breeding season. Opportunities are emerging for more objective methods of semen evaluation to be used alongside standard microscopy, such as computer-assisted semen analysis (CASA) for motility and flow cytometry to assess morphologic defects. (Also see Breeding Soundness Examination of Bulls.)

During the breeding season, the bull should be watched closely for mating behavior. The standard recommendation is 25 cows per bull. There are significant variations in this ratio, depending on the breeding soundness and libido of individual bulls, differences in terrain, and length of breeding season.

The weight loss that develops in bulls during the breeding season should be restored during the off-period, but overconditioning should be avoided.

Last full review/revision April 2015 by Jonathan Statham, MA, VetMB, DCHP, MRCVS

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