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NEW GENETIC INDEX WILL HELP THE FIGHT AGAINST TB
Holstein breeders are accustomed to using genetics to improve the health of their herds. Now they can reduce their herd’s chances of contracting TB, as a new index is launched.
H
olstein breeders now have a new genetic index to help them make breeding selections following the launch of the TB Advantage by AHDB Dairy in January 2016.
The index can be added to existing selection criteria to help breed dairy cows with better resistance to bovine tuberculosis (bTB).
Although no one in the industry is claiming the TB Advantage will be a cure-all for bTB, it certainly has the scope to improve an animal’s resistance to the disease and, like all genetic improvement, benefits will accumulate over the generations, says AHDB Dairy’s head of genetics Marco Winters. “The index has been developed following extensive research undertaken by the University of Edinburgh, Roslin Institute and Scotland’s Rural College and supported by DEFRA, the Welsh Government and the Agriculture and Horticulture Development Board.
“By using data from the Animal and Plant Health Agency from animals which react to the official bTB skin test and are sent to slaughter, they have been able to identify patterns of resistance among different bloodlines,” he explains. The breeding patterns they have established form the basis of the genetic index, which is the first genetic index for bovine TB to be used in the world.
“The introduction of the TB Advantage continues a long tradition of innovation in genetic indices in the UK. Holstein UK was the first organisation in the world to introduce locomotion scoring for dairy cows and was also pioneering in the development of an index for body condition score.
“Since those days, the industry has become accustomed to using genetic indices for health and fertility, and has seen significant genetic improvement in the traits which have been targeted,” he says.
He particularly cites somatic cell count which has been found to have a similar heritability to bTB resistance.
“The heritability of bTB resistance is about 9%, which means that of all the variation we can detect in the trait, about 9% is due to genetics,” he says. “This is on a par with some other health traits, including somatic cell count, which Holstein breeders have been improving through genetic selection for a number of years. “All of this gives us confidence that the TB Advantage will be an effective tool in the fight against bTB, but it does not detract from the other control measures which must continue to be taken as part of the broader disease eradication plan,” he says. Continuing with the usual measures of biosecurity, the protection of cattle against
Marco Winters Head of genetics, DairyCo
infected wildlife and the routine monitoring of cattle for the disease remain core components of the strategy to eliminate TB from the national herd.
Using the TB Advantage The TB Advantage provides an indication of the degree of resistance to bTB a bull is predicted to pass on to his offspring and, like all genetic indices used by Holstein breeders, it is a Predicted Transmitting Ability (PTA), he adds.
Expressed on a scale which typically runs from -3 to +3, a positive index is desirable. “For every point of a bull’s TB Advantage, 1% fewer daughters are predicted to become infected during a TB breakdown,” explains Mr Winters, adding that the difference between daughters of the best (approx +3) and the worst (approx -3) bulls is, therefore, about 6%. “This means that six fewer cases of bTB could be expected in every 100 cows in one generation when the best bulls are chosen over the worst. “And as with all genetic improvement, the benefits are cumulative, building up over the generations.” However, Mr Winters emphasises that the TB Advantage should form only part of a broader breeding strategy.
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