New genetic index will help the fight against bovine TB

Published 8 January 16

A new genetic index will be published on 19 January 2016 which will help farmers in the UK breed dairy cows with better resistance to bovine tuberculosis (bTB).

Called the TB Advantage, the index will bring an extra control measure to bear on this infectious disease of cattle which has brought long-term financial and social hardship to large sectors of the farming industry.

The index has been developed following extensive research undertaken by the University of Edinburgh, Roslin Institute and Scotland’s Rural College (SRUC) and supported by Defra, the Welsh Government and the Agriculture and Horticulture Development Board (AHDB).

It will give an indication of an animal’s genetic susceptibility to bTB, highlighting those which may be more prone to infection or – at the other extreme – those which have a higher degree of resistance to the disease.

By selecting bulls with a high score for TB Advantage, farmers will be able to breed better resistance into their herds, which – like all genetic improvement – will accumulate over the generations leading to long-term benefits.

Used alongside existing bTB control measures – including high levels of biosecurity, protecting cattle against infected wildlife and routinely monitoring cattle for the disease – the index is expected to play a part in the plan to eradicate bTB from UK farming.

It is the first genetic index in the world to be developed to help farmers breed better resistance to bTB into their herds.

The TB Advantage will be expressed on a scale which typically runs from -3 to +3, similar to many genetic indexes farmers are familiar with using. The average TB Advantage for all bulls with an index is zero.

Marco Winters 2016Almost all Holstein bulls – both daughter-proven and young genomic sires – will have an index, and those female Holsteins which have had their genotype measured will also be scored for TB Advantage.

Following the initial index run for Holstein bulls which will be published at the time of the British Cattle Conference on 19 January 2016, the TB Advantage will be published by AHDB Dairy as part of the routine genetic evaluations three times a year.

Marco Winters, head of genetics for AHDB Dairy says: “Tackling any problem through breeding is a long-term, sustainable approach and can yield worthwhile rewards.

“However, breeders of dairy cattle have to consider a number of traits which are important to their business and their cattle, and breeding for TB resistance should be only a small part of their broader breeding strategy.”

Professor Mike Coffey, who led the team at SRUC in analysing over 650,000 cattle records as part of the process of developing the index said that the heritability of bTB resistance is about nine percent.

“This means that of all the variation we can detect in the trait, about nine per cent is due to genetics,” he said. “This is on a par with some other health traits, including Somatic Cell Count, which dairy farmers have been improving through breeding 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 said.

“This index is another tool in the breeding armoury and once a farmer has shortlisted the bulls which meet his other chosen breeding criteria, it will always be best to avoid those which have a poor index for TB Advantage,” added Mr Winters.

“We know that improvement through breeding is a long-term approach to any problem but this will stack the odds of fighting bTB in the farmer’s favour and play a part in the plan to eradicate bTB from the UK,” he says.