Ava Moynihan and Simon Lanigan from ICBF presented a board on “Breeding for TB Resistance” at the recent Moorepark Open Day. Details of their board and more information can be seen below.
Why breed for TB resistance?
Genetic selection for Bovine Tuberculosis (TB) can be seen as a complementary strategy to the TB eradication program already in place by the Department of Agriculture, Food and Marine (DAFM). Research shows that certain family lines of cattle tend to have a higher prevalence of TB reactors than other cattle from other family lines. Data shows that some bulls that had many progeny in TB infected herds, none of their progeny became TB reactors, while other bulls that produced progeny in the same TB infected herds, were diagnosed as TB reactors.
Breeding values for genetic resistance to TB was launched by ICBF in 2019 to help dairy and beef farmers to maintain healthier cattle. Just as genetics dictates how well an animal can produce milk or gain weight, animal health is also under genetic control. Cattle that are bred for resistance to TB have a greater ability to fight off TB, if they come in contact with the disease. This can result in fewer TB reactors, fewer TB-breakdowns, and fewer cattle diagnosed with liver fluke infection. Breeding for resistance to TB should aid the acceleration the rate of TB removal from Ireland as well as reduce the prevalence of TB without having any major negative ramifications on other traits.
Understanding TB Predicted Transmitting Ability
Each animal’s breeding value for resistance to TB is expressed as the predicted prevalence of TB in that animal’s progeny. Therefore, lower breeding values (PTA %) mean that fewer progeny are expected to be diagnosed with TB. This means that if a bull has a breeding value of 5% for TB resistance, on average, 5% of his progeny are expected to be TB reactors in their lifetime
To achieve the most profitable herd that is also more resistant to TB, select cows and bulls for breeding that have the highest overall breeding index (i.e., EBI, Replacement Index, or Terminal Index) with the lowest breeding value for resistance to TB.
Does selecting for TB resistance reduce production traits and EBI?
No. To demonstrate this we looked at 1000 calves with an EBI greater than €350 (Figure One below).The table clearly shows that you can select for High EBI animals, with a good health SI (includes TB PTA%), without compromising on production traits.
How can I protect my herd?
Farmers can protect their herd by selecting bulls and cows with high EBI and low TB PTA %. To see more rapid improvement in your herd, aim to use bulls with the lowest possible TB PTA%. This can be done using the traffic light system, outlined below.
Traffic Light system
Here at ICBF, we have developed a traffic light system which herdowners can utilise to make informed breeding decisions. This colour-coded system makes it easier to compare animals. This visual tool can help identify good, moderate and poor rated animals for TB PTA% on their animal profile.
If the PTA for TB is red (poorest TB values) we advise to avoid the bull. If the PTA value for TB is orange (average TB values), we advise to proceed with caution if using that bull. If the value for TB is green (best TB values), we advise that this bull is good to use.
- If PTA % value for TB is red, avoid.
- If PTA % value for TB is orange, proceed with caution.
- If PTA % value for TB is green, good to go!
When looking for TB PTA % of the animals within your own herd, login to your HerdPlus EBI profile, in which the TB PTA %, (alongside it being colour coded according to traffic light system), will be visible.
Figure two above, shows an example herd profile available via your HerdPlus EBI profile. Within this example, the EBI of the cows range from €207 to €265. However, when we focus on the TB PTA % values, they vary from 6.8% (colour coded green) to 9.8% (colour coded red). Therefore, it is important to know your TB PTA % status in order to breed for and achieve the best possible results for TB resistance within your herd.
To gain more guidance on breeding for TB resistance, information can be found at https://www.icbf.com/wp-content/uploads/2019/01/TB_Fluke_Helpsheet_v2.pdf and for a more detailed explanation see; https://www.icbf.com/wp-content/uploads/2019/01/TB_explanation.pdf