We should be thinking about bulls at the start of AI rather than at the end of it. It is advisable to have bulls on farm at mating start date to allow enough time to prepare them for the natural mating period. They should be vaccinated and socialised prior to work and if they are unvaccinated, at least six weeks are required prior to joining for the vaccines to be fully protective.
At CVC we recommend all bulls are vaccinated for “Vibrio”, a venereal disease that has the potential to cause early term abortion. Unvaccinated animals require two shots four weeks apart, with the second dose given at least two weeks prior to the start of bull mating. Previously vaccinated animals require an annual booster given two weeks prior to work.
It is also advisable to consider testing for “Pestivirus” in all bulls that have not received the “Pestigard” vaccine. We are learning more about this disease each year, and although vaccines are available, their use is often not required. All positive bulls should be slaughtered immediately as they pose a significant threat to the reproductive performance of your herd. For obvious reasons, all vaccinations and screening tests should occur prior to the introduction of bulls to any animal on farm.
A common problem during the natural mating period is lame bulls. Lame bulls pose a significant risk to the empty rate of your herd, despite many showing no reduction in libido. Sore bulls will not mount correctly, often will not finish the job, and if they do, any infection present will likely reduce the motility and viability of their semen.
There are several management strategies to minimise the incidence of lameness in your bulls:
Socialise your bulls prior to joining – if they are fighting, they aren’t mating!
Ensure suitable numbers of bulls are being used for your herd
Rotate the bull teams to ensure regular rest periods
Minimise the walking bulls are required to do – avoid yarding them with the cows on concrete
Preventative trimming or blocking bulls immediately prior to work
Avoid feeding excessive concentrates prior to and during the joining period
The most common reason dairy farmers have too many empty cows is due to insufficient bull numbers. The bulls selected have to work harder than they should, they break down and then very few cows are actually joined. Current guidelines suggest 3 bulls per 100 cows at mating start date, i.e. for a 400 cow herd 12 bulls are required. This increases to 4 bulls per 100 cows if synchrony is used.
The bulls should be split into “bull teams” usually by size, age and temperament to reduce the likelihood of fighting. How these teams are managed is up to the individual, however it is suggested they work for no longer than 7 days at a time.
For the example above, you could use 3 teams of 4 bulls, rotating the teams every four or five days. However, some people have had success rotating the teams more frequently; some even have day and night teams. The great advantage of the later scenario is very few sore feet; the disadvantage is drafting the bulls in the paddock! Dairy bulls are generally used from about 18months of age for 2-3 years before being replaced.
Vibrio vaccine is available in the clinic as individual shots, so you don’t have to buy a large bottle and discard the unused doses.