Niall Collins
Question:895. Deputy Niall Collins asked the Minister for Agriculture, Food and the Marine the methodology used to identify animals that are deemed to be at high risk of contracting tuberculosis. [23909/20]
View answerTuesday, 15 September 2020
Questions (895)
Written answers
Ongoing research over many years has identified the risk factors which can put animals and herds at higher risk for Bovine TB. Much of this research has been performed in Ireland, Northern Ireland and Britain with similar results emerging. The Centre for Veterinary Epidemiology and Research Analysis (CVERA) in UCD has been responsible for much of the research in Ireland but similar studies on risk emanate from Northern Ireland and Britain also. The results of these epidemiological analyses inform the Department's advice and initiatives on helping farmers to reduce risk to TB on their farms. Examples of the issues which can put an animal or a herd at a higher risk of TB include:
1. Animals that had previously tested inconclusive to a TB skin test, but had passed all tests thereafter are higher risk. This is because the skin test will identify only 80% of infected animals, on average, because of the failure in some cases of the animals immune system to mount a strong enough reaction. Because of this, previously inconclusive animals are restricted to the herd of disclosure for life and are removed if that herd experiences a TB breakdown.
2. Animals which had been present during a TB breakdown previously are at a higher risk for TB. The reason for this is similar to inconclusives higher risk. The animals were exposed to TB during the original breakdown and, in some cases, these may have become infected but for immunological reasons some may not react to testing and therefore remain as false negatives, i.e. clear animals. This phenomenon is called residual TB and is a significant reason why it can take up to 10 years for a herd to return to normal levels of risk after experiencing a TB breakdown. It is advisable for animals that were previously present during a breakdown to be considered for culling when decisions are being made on farms on which animals to retain, if the herdowner wishes to reduce the risk of a TB breakdown.
3. Animals which have had multiple movements are at higher risk for TB than animals which have not. This is associated with the increased potential for exposure to sources of infection because of movement between different herds and lands.
4. Significant variation in inherited susceptibility to TB has been identified and farmers can now choose to breed from bulls whose offspring are more resistant to TB.
5. Many studies have reported increased prevalence of TB with age meaning older cows are higher risk for TB. This is associated with increased chance to exposure to infection sources. This factor should be considered when making culling decisions to increase herd resilience.
The definition of a closed herd is one where none of the animals within the herd have been purchased from, or returned from, outside the herd. Animal Health Ireland and Teagasc have published advice over many years on the benefits for animal disease in maintaining a closed herd. This crucial biosecurity measure is beneficial across all cattle diseases – not just TB.
My officials provide this advice to farmers so that they can make choices appropriate to their own farming circumstances to reduce their risk of TB, should they so wish.