The Genetics of TB

AHDB has recently launched TB Advantage, which is a new genetic index to help dairy farmers make informed breeding decisions. Rose Jackson explains more.

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Rose Jackson explains more about AHDB Dairy’s TB Advantage scheme.

AHDB has recently launched TB Advantage, which is a new genetic index to help dairy farmers make informed breeding decisions to select cows which have an improved resistance to bovine tuberculosis (bTB).

This is the first genetic index of its kind in the world. Using data on over 650,000 Holstein cows who have bTB data recorded by the Animal and Plant Health Agency (APHA) more resistant bloodlines have been identified.

Heritability is 9% which is about the same as SCC so in the long term, breeding for more resistant animals should have a positive effect on the TB status of a herd. That said, as for SCC control, environmental and biosecurity measures are still critical in the management of bTB.

The TB Advantage is currently available for all dairy breeds with work under way to establish if the index can be extended to beef breeds. TB advantage is available for all UK proven and genomic bulls. We can also obtain a figure for individual females through our Genomic testing service, Clarifide.

How to use TB Advantage

AHDB Dairy explain more about how to use TB advantage (take from AHDB Dairy).

TB Advantage can be used as part of a range of important genetic traits to form a balanced breeding plan for the herd; this way the herd’s strengths are maintained and weaknesses improved. The degree of emphasis on the TB Advantage may further depend on whether the herd is within or close to a TB affected area or not.

The index indicates the degree of resistance to bTB a bull is predicted to pass on to his offspring and is expressed on a scale which typically runs from -3 to +3 and as for most other traits, positive values are desired. For every +1 point in the index, 1% fewer daughters are expected to become infected during a TB breakdown.

TB Advantage has small but favourable relationships with all traits currently in the UK breeding indexes, £PLI and £SCI. Selecting bulls with positive TB Advantage therefore will, on average, have no detrimental effect on any other trait. However, farmers should look at each bull on a case by case basis, as any individual could have weaknesses that should be avoided for a particular herd.

The reliability for the TB Advantage ranges from 20 to 99%, with an average reliability of 65% for bulls with UK daughters, and 45% for those with a genomic index only. Although the reliability of genomic predictions for the TB Advantage is currently less than for some other indexes, it can still be used as part of a dairy herd’s breeding strategy and has shown to be valuable in predicting future performance.

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