The ins and outs of service bulls

Trudy and Matthew Holmes.


By Frank Portegys – DairyNZ consulting officer in Waikato


21 August 2018

You’ve just had your last day of artificial breeding (AB) and now you’re ready to let the bulls do their job.

No more heat detection, no more tail painting, no more drafting out cows, no more waiting for the AB technician – the pressure’s off, right?

It’s tempting to think that, but good planning and management is still essential if the tail end of mating is to be successful.

It’s easy to underestimate the number of bulls needed, which can lead to a lower in-calf rate. You should have at least one bull for every 30 non-pregnant cows, (one bull to every 25 yearlings), plus the same number resting so you can rotate the bulls. If bulls are over worked their fertility will quickly drop off. The below table has some good guidelines.

Helen Thoday

Now let’s talk biosecurity. Bringing any new stock onto your farm is a biosecurity risk, and bulls are no exception.

Unless you’re rearing your own bulls, you will need to either purchase or lease service bulls, so you’ll need to minimise the risk of introducing diseases to your herd, such as Mycoplasma bovis, bovine tuberculosis (TB), bovine viral diarrhea (BVD), or a venereal disease.

Choose virgin bulls, if possible. If not, discuss testing for venereal diseases (Trichomoniasis and Campylobacter) with your vet.

Insist bulls are certified free of TB, BVD, Infectious Bovine Rhinotracheitis (IBR) and Enzootic bovine leukosis (EBL), and blood test negative for Johne’s disease. Again, discuss with your vet.

Bull suppliers can have their mobs tested for M.bovis. Given the possibility that infected animals may shed bacteria intermittently, testing may not completely exclude the possibility of infection, so results will be reported as “not detected” rather than “negative”. Multiple negative tests from bulls from the same property will offer some confidence.

It’s important to know the health history of the herd you receive the bulls from. Bulls should arrive properly identified and accompanied by their movement history. Make sure you let the vendor or agent know that you expect to be provided with these details.

On arrival, ensure the bulls are held separately from the herd for at least a week to assess their health and to make sure all NAIT records are up-to-date and correct.

Last but not least, remember to take extra care when around bulls as they can be extremely unpredictable. It’s a good idea to run through some refresher training with your team to make sure they’re aware of the warning signs to avoid being attacked.

For more information on how to get the best out of your bulls and maximise your reproduction performance, visit

Frank Portegys

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