At the recent ICBF and Sheep Ireland genetics conference in Athlone, Dr Siobhan Ring of Teagasc gave a presentation outlining work currently being done to establish a link between genetics and the prevalence of TB in cattle.

Dr Ring, who is carrying out this study under the guidance of Professor Donagh Berry of Teagasc, explained the basis for this research at the beginning of her presentation: “Why is it that only some cattle in herds get TB when, theoretically, all animals in the herd are exposed to the same factors?”

This would lead to the possibility that genetics plays a role in the prevalence of TB in certain animals and not others.

Observations

As part of the research, multiple herds with TB infection were examined.

By doing so, it was identified that less than 5% of some sires’ progeny within a TB-infected herd had contracted TB, whereas 30% to 40% of other sires’ progeny had contracted TB from similarly infected herds.

In short, in TB-infected herds, the prevalence of TB in stock varied significantly between sires.

Following on from this, the research has concluded that the heritability of TB is as high as 12%.

In comparison, the heritability of direct calving ease is just 9%.

With that, Dr Ring explained the potential impact this could have for the reduction of TB in Ireland.

If farmers were to select purely for health traits, the link between genetics and TB shows that the prevalence of TB could be reduced by 1.9% annually.

TB prevalence also varies between indices.

On average, high-EBI and replacement index bulls have a lower TB prevalence, whereas high-terminal index bulls have a higher TB prevalence.

Considerations for use

The potential impact of this research could be significant in terms of reaching the end goal of TB eradication in Ireland.

Dr Ring explained that one such impact could be to “screen-out the worst males and females” to lower the risk of exposure in herds.

This threshold could become lower over time, ie screen off animals with a risk of 30% first, and then lower the threshold to 25% and so on, thus constantly reducing the risk of TB infection through generations.

Future plans

With this research now acting as the foundations, the future plan is to roll out an economic breeding value for TB in the spring of 2019.