Building bTB resilience through breeding (Feb 22)

Can long-term breeding plans reduce the impact bovine TB can have on your herd and business? We spoke to a producer and a geneticist to find out more.


TEXT SARAH TOMLINSON



Can changes to the way cows are bred help to soften the catastrophic blow of a bTB breakdown? Anglesey-based producer Tudur Evans thinks so. He runs a 160-cow Holstein herd, based at Rhosbadrig, and decided to change the way he breeds replacements to help mitigate the impact bTB could have on his business. In February 2020 the unit suffered its first bTB breakdown, which Tudur says devastated the business. Once a reactor has been identified, cattle are not permitted to leave or enter the holding. And these movement restrictions stay in place until two consecutive clear bTB skin tests have been completed.


Tudur took on running the family herd in March 2020 and decided to take steps to ensure the dairy business would be able to survive financially if they were unlucky enough to suffer another bTB breakdown.


“We switched to using sexed semen on our top cows. We didn’t want any black-and-white bull calves on the unit to rear. These would typically leave the farm before they were six weeks old, but if movement restrictions caused by bTB reactors are put in place then they can’t,” he explains. “And we wanted to breed beef calves that would have a market, even if we did suffer a bTB breakdown again. So we now use an Aberdeen Angus sire on cows we don’t want to breed replacements from to produce calves an approved finishing unit would want to buy. It has been the best thing we have done and not only for peace of mind should we have another breakdown, but also for the business as a whole.”


Technology and data can also help with reducing the risk of bTB to the herd by looking at the heritability of bTB resistance.


Geneticist Mike Coffey, from Scotland’s Rural College, says TB Advantage, the only genetic index in the world that measures bTB resistance in dairy cattle, can help UK producers to make sire-selection decisions and reduce their herd’s risk of contracting the disease.


Additional tool


“The index isn’t a replacement for good biosecurity, testing and culling, and all the other measures used by producers, vets and the Government to control this devastating disease,” he says. “But it is an additional tool that producers can use to increase the background resistance of their herd on which these other control measures are layered.” The index was developed using data from the UK’s bTB test results. All cattle records were subjected to a genetic evaluation, similar to that conducted for all other traits. Cattle are compared within groups of similar cattle in a herd, so affected and non-affected animals by sire are compared within herds.


More resistant


“The end result is the TB Advantage predicted transmitting ability (PTA ) – an estimated breeding value that is presented as a number. The more positive a value the better in terms of helping to reduce the incidence of bTB,” explains Professor Coffey.


“The index allows producers to select sires whose daughters are predicted to be more resistant to bTB than daughters of another bull. If the bulls are of equal merit for all the other traits of interest to the producer, then logic says to choose the better TB Advantage bull. Repeatedly making those choices results in a herd of cows that are more resistant to bTB, and fewer cows becoming bTB positive.


“It is difficult to describe how the TB Advantage PTA relates to outcomes seen on farm due to the complex nature of the transmission of bTB between animals,” adds Professor Coffey. “But we do know that using the index works, and it reduces the number of cows contracting bTB.”



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