High levels of rainfall or another factor closely linked to wet weather conditions emerged as a significant driver of high rates of TB in the Burren’s cattle herds up to 2020.

That is according to a study carried out on TB in the Burren between 2015 and 2019 which was recently published in the Irish Veterinary Journal.

The study examined possible causes for the Burren witnessing higher rates of bovine TB than were seen across the country as a whole from as far back as 2005, as well as disease levels higher than the areas surrounding it.

Test results from 939 herds with land in the Burren fed into the analysis and some 27% of these herds saw at least one reactor during the five years of testing.

This was despite the Burren’s herds seeming on paper to be at a low risk of going down with TB.

The area generally has smaller herds than are typically seen nationwide, a low proportion of these are dairy or finishing herds, and these herds see fewer inward cattle movements than is the case in the national herd as a whole.

All of these factors would suggest a lower incidence rate of TB in the Burren than was the case across the country.

While the Burren had more badger setts located within 2.5km of a herd than was seen nationally, this could at least partly be put down to more sett searching efforts in the area than elsewhere, given its history of herd breakdowns.

What’s different

The researchers also noted that badger abundance appeared similar to other regions of the country and badger control operations were deemed to operate as efficiently as elsewhere.

The main factor flagged in the study’s analysis of the Burren’s TB levels was the “relatively high” levels of rainfall in the region.

It stated that generally within the Burren, the areas which saw the worst TB incidence were those which got the most rain. Previous work had established a link between temperature and moisture to TB in herds across England and Wales. This was on top of similar rainfall-TB relationships identified in studies completed on herds in Co Wicklow and in the west.

The researchers stated that harsh weather conditions could push herds into seeking shelter together and this could combine with the possibility of contact with TB infected wildlife.

High levels of rainfall, they commented, could reduce feed quality or the effects of exposing cattle to poor weather could also explain why the disease prevalence was so high in the Burren.

They also proposed that the bacteria which causes bovine TB - Mycobacterium bovis – may survive better in damp areas which receive less sunlight.

As the proportion of cattle with TB undetected until post-slaughter inspections took place was broadly similar in the Burren as elsewhere, the researchers suggested that it was unlikely that rainfall was affecting the reliability of the skin test.

Progress since

There was a “sharp decline” in the Burren’s incidence of TB since 2020 to such an extent that it came into line with the rest of the country by 2023.

These years and the factors behind this improvement were beyond the scope of the study, but the researchers did note that a ramping up of Department of Agriculture interventions, badger culling, outbreak investigations and six-monthly TB testing in the Burren area may have been among the reasons for it.