The general decline in fertility and increasing dairy herd production demands, make mop-up bulls critically important. Bulls on many dairy farms are not being effectively used and are often a danger to the farmer and farm's economic viability.
Effective mop-up bull management should be a priority for every dairy farmer in order to avoid the need to rebreed cows or heifers. Appropriate bulls should be capable, healthy and safe.
A ratio of one bull to forty cows (joined and unjoined) should be used, with this number increasing if there is a tighter mating period. This number relates to both his ability to identify cows on heat and his serving capacity. One of the easiest assessments of a bull's serving capacity is scrotal circumference and this should be considered when buying bulls. One method available to assist in reducing the risk of unsatisfactory joining results and maintaining the bull's sexual interest is rotating his team between a rest paddock and the herd, with a second bull team also running an alternate rotation. A week is generally a sufficient rest period for a healthy bull team.
Bulls should be grouped with equivalent sized bulls and ideally they will have grown up with one another. When managing bull groups try to avoid shuffling bulls between groups as each time a new bull enters a group, the whole social hierarchy will need to re-establish and this process can lead to stress and injury. Stress should be avoided due to its impact on future sperm production, with both environmental and management stress having an impact. Included in this is nutritional stress so bulls need to be adequately fed.
Bull health is the most important factor limiting the reproductive potential of bulls on farm. In many instances the bulls are not at an appropriate condition score, not vaccinated or are afflicted with some form of aliment. Ensuring the bull is free from injury and/or structural defect is a priority when assessing a bull's ability to get cows in calf. The bull's conformation is important due to the strenuous nature of mounting cows. A bull with foot, leg or back issues will struggle to mate cows and if the issue is significant enough, may not even attempt to mount.
Eyes, nose and mouth are also crucial because a bull requires these senses to identify cows on heat. The final health component is vaccination, due to the bull's ability to transfer disease to a large number of the herd.
This means vaccinating bulls for '7 in 1', pestivirus and vibriosis, as well as any other vaccine you are giving the cows. Have the vet check them at least one month before the joining period.
Personal safety is also an important issue that deters many dairy farmers from using bulls and as a result is costing them in reduced conception rates and a need to spend extra cash on AI programs.
This issue is best managed through a zero tolerance approach to aggressive behaviour. If the bull is aggressive, either towards people or other cattle, definitely don't keep him. Let him finish the season and replace him for next year.
In summary: unhealthy bulls do nothing but cost you money and waste your time. A healthy bull can improve the fertility and the economics of your farm system. For more information on bull management or selection contact Matt Reynolds, DEPI Warrnambool, telephone 0408 534 595.