A new analysis published yesterday indicates that only 6% of the transmission of bTB to cattle herds is from badger-to-cattle contact. Fresh analysis of the data collected from the Randomised Badger Culling Trial (RBCT), conducted under the previous government, published by Imperial College goes on to say that although the initial transmission rate is low, this source of infection is responsible for up to half of the cases of TB in a high TB incidence area. The mathematical model used suggests that 5.7 per cent of transmission to cattle herds is from badgers to cattle, with the rest of the contribution attributed to badgers due to cattle-to-cattle transmission within and between herds.

Professor Christl Donnelly, who lead this statistical research, told the BBC that "The 6% figure tells you about introductions into herds and that tells you that 6% of the introductions into herds come from badgers; 94% of them come from other cattle herds." However, this data is from trials which predate new cattle movement restrictions designed to prevent the spread of the disease within and between herds. As a result of these measures, the onward transmission should be significantly reduced. 

The report states that although an average overall contribution from badgers of at least 38% indicates their importance in the disease system (at least within the areas analysed), it does not indicate how this contribution might best be limited. The authors conclude that "Our findings show that badgers play a major role in maintaining M. bovis infection in England's high incidence areas, but also indicate that badger-to-cattle transmission events are amplified by onward transmission within local cattle populations. Hence, our findings inform debate even if they do not point to a single way forward."

The researchers' refusal to make recommendations based on their findings reflects the ambiguity and margin of uncertainty of the study. As a result, it will be for policy makers and pundits to debate whether Defra's chosen approach of badger culling is appropriate, or whether, as John Bourne, the vet who oversaw the RBCT trials recommends, cattle-based measures could be tightened further.