Illegal persecution of badgers does not reduce infection risk of bovine tuberculosis (TB) in cattle and may play a role in maintaining epidemic hotspots according to researchers at Queen’s University Belfast.

The Institute for Global Food Security collaborating with the University of Glasgow and the Agri-Food and Biosciences Institute, found that illegal disturbance of badger social groups contributed significantly to new bovine TB breakdowns in nearby cattle herds.

The study, funded by the Wellcome Trust, and published in Natural Scientific Reports, found that about 5 per cent of badger setts in Northern Ireland had recent signs of illegal interference or persecution. For example, recent digging indicative of badger baiting, sett entrances being blocked with soil, boulders and branches or being pumped full of slurry, setts being ploughed over or having farm debris dumped on top, damaged by livestock trampling, and development such as the construction of roads or newly built houses.

Dr David Wright, who led the study said “Whilst interference with badger setts was relatively rare it was clustered in known bovine TB hotspots in cattle and we hypothesised that those taking action against badgers may actually contribute to maintaining the disease. So we were interested in investigating the interaction of cattle and badgers in disturbed and undisturbed populations.”

Bovine TB has proven difficult to control and eradicate in cattle costing the UK Government more than £100M in annual testing, slaughter and compensation. The badger has been identified as a major factor contributing towards the difficulty of eradicating the disease as it is a wildlife reservoir of infection. However, the relative importance of badgers in maintaining the cattle epidemic is extremely controversial.

Both the British and Irish Governments have invested in large-scale regional badger culling programmes in an attempt to control the disease. In Britain, badger culling has been associated with a decreased prevalence of TB in cattle inside cull areas, but an increase in neighbouring herds such that the total impact has been judged negligible. Moreover, culling operations are expensive, have animal welfare implications, and are difficult to implement. The proposed reason for the limited effect is due to so called ‘perturbation’ as culls are never 100 per cent effective with surviving badgers migrating due to social group disruption spreading the disease as they go. Nevertheless, in the Republic of Ireland where badgers have been removed over larger, more isolated regions, it has been claimed that badger culling is effective in controlling the disease in cattle.

The new study found that farm-level risk factors, including the number of cattle movements, frequency of international cattle imports, previous bovine TB history and the proximity of neighbouring farms with a bovine TB history were far more strongly associated with new cattle herd breakdowns than measures of the badger population or badger persecution. This suggests that disease control could be improved further by increased frequency and accuracy of cattle testing, development of more sensitive tests and improved farm biosecurity.

Nevertheless, the risk of bovine TB breakdowns in cattle was significantly elevated in areas of high badger social group density and high rates of persecution through sett interference.

Dr Neil Reid, Lecturer in Conservation Biology at Queen's University, explained “The relationship between badger persecution and bovine TB in cattle could either be because persecuting badgers perturbs the population stimulating spread of the disease or farmers are more likely to persecute badgers if their livestock have previously had a TB breakdown. We can’t say which way round the relationship is but we can say that persecuting badgers certainly does not lower TB risk in cattle, it is illegal and may make the situation worse. Farmers should be aware of the risks incurred by disturbing badger setts.”

This is the first study to highlight the potential importance of badger population disturbance, rather than officially sanctioned Government culling, in sustaining the bovine TB epidemic in cattle.