As part of the latest round of changes to the EBI, the risk of TB is now fully integrated into the breeding index. Prior to this, EBI was a standalone feature in the database where farmers could look up the predicted transmitting ability (PTA) of a bull for TB.Previous research found that genetics is responsible for 12% of the variability in TB infection and the animal’s ability to fight it. There are some AI bulls that, even with many progeny in TB-infected herds, had offspring that became TB reactors. On the other hand, there have also been bulls with four out of 10 of their progeny in TB-infected herds diagnosed as being TB reactors. The benefit of using animal breeding to reduce TB is that breeding is permanent and cumulative, unlike other control methods like vaccines for badgers.
As part of the latest round of changes to the EBI, the risk of TB is now fully integrated into the breeding index. Prior to this, EBI was a standalone feature in the database where farmers could look up the predicted transmitting ability (PTA) of a bull for TB.
Previous research found that genetics is responsible for 12% of the variability in TB infection and the animal’s ability to fight it. There are some AI bulls that, even with many progeny in TB-infected herds, had offspring that became TB reactors. On the other hand, there have also been bulls with four out of 10 of their progeny in TB-infected herds diagnosed as being TB reactors. The benefit of using animal breeding to reduce TB is that breeding is permanent and cumulative, unlike other control methods like vaccines for badgers.
The PTA for TB is now part of the health sub-index in the EBI and the best place to find it is on the ICBF website when you click into the bull’s details. Munster Bovine seems to be the only large station to have the value for TB on its catalogue.
Farmers should look at the TB value for all bulls being used and avoid those that increase the risks of contracting TB in the event of exposure. \ Donal O Leary
The TB figure is given as a percentage, which represents the percentage of the bull’s progeny that is expected to get TB in the event of being exposed to the TB bacterium. According to Siobhan Ring from the ICBF, the range in most bulls is between 1% and 14%, with the average being 7.5%. So, choosing bulls that are lower than 7.5% for TB means that they are less likely to get TB, and choosing bulls higher than 7.5% means they are more likely to get TB.
“The advice is still along the same lines now – choose high EBI as the first port of call, then look for bulls that have a lower PTA for TB. The most recent validation based on 2021-2022 reactors show that those with the worst breeding values for TB had the highest prevalence of TB and had a tendency for the highest probability of TB infection,” Siobhan says.
“Animals with a very poor breeding value for TB were 17% more likely to show up as a TB reactor in a herd test or at slaughter than those with an average breeding value, and were 20% more likely to show up as a reactor than animals with the best breeding values for TB.”
Looking at the bulls on the Active Bull List, most of them are unfortunately above 7.5% for TB. Kilfeacle Pivotal, a widely used AI-bull over the last few years, has a PTA for TB of 11.44%, meaning all of his progeny have a higher risk of TB than most other bulls.
Of course, genetics is a trade-off; one usually has to sacrifice something in order to gain something else and that’s always a challenge with multi-trait indexes. For some farmers, those located in TB hotspots for example, the impact of genetics should be looked at more closely than for others who have never had a TB outbreak. However, in all cases the TB value should be looked at when choosing bulls, and those with a high value should be avoided.
This is a subscriber-only article
SHARING OPTIONS: