Warning -- choose your bull with care
Dairy farmers are using a range of tactics, including “due diligence”, quarantine and opting for virgin bulls to protect their cows from Mycoplasma bovis, according to DairyNZ.
The disease, which was mainly spread via close physical contact with infected animals, made using bulls that had been exposed to other stock an added risk, DairyNZ response manager Hamish Hodgson said.
Some farmers were thinking twice about continuing to use a combination of artificial insemination and bulls, and considering extending AI to remove bulls from the equation altogether, or reduce the number required.
DairyNZ had received a number of inquiries from farmers over recent weeks wanting more information to weigh up the risks and benefits associated with each approach.
Mr Hodgson said the best thing farmers could do to protect their herds and farms was to “do their homework”, but there was no silver bullet. Both AI and bulls had pros and cons.
While a lot of farmers had been considering adapting their usual approach, most weren’t making drastic changes, however. The majority appeared to be sticking with a combination of AI and bulls, despite reports that some farmers were shying away from using bulls.
“There have been some murmurs that farmers were going to avoid using bulls and just use artificial breeding, however, after considering the risk and the cost to their businesses, few have elected to proceed with a full AI system due to the likely lowering of overall fertility stats, perceived costs, and increased labour for accurate heat detection,” Mr Hodgson said.
“Those using bulls should still do their due diligence, check where they’ve come from and if they’ve been in herds with a history of disease. This is extremely important, especially if they’re older bulls that have done a few mating seasons on other farms.”
He understood there had been a spike in demand for virgin bulls that had had minimal exposure to other animals, while farmers had also been asking about M. bovis tests for bulls.
“There is a polymerase chain reaction (PCR) test that is highly sensitive and will detect if M. bovis is present in a sample, but the complex nature of the disease can make this challenging,” he added.
“Because infected animals only shed the bacteria intermittently, it is dependent on M. bovis being present where the sample is taken, and on the day the animal is tested.
“This means a result of ‘not detected’ doesn’t necessarily mean it’s disease-free. That’s why we’re recommending farmers gather as much information as possible about the source of any bulls and don’t rely on PCR results.”
DairyNZ recommended that farmers keep bulls apart from their main herds for at least seven days to allow time for the disease to present itself if they’re infected.
Any farmer concerned about the health of bulls should contact their veterinarian before introducing them to their herd.
■ For more information on mitigating the risks of M. bovis this mating season, go to dairynz.co.nz/mbovis