By the mid-1970s the evidence that badgers played a significant role in infecting cattle was sufficiently strong that the UK Ministry of Agriculture, Fisheries and Food (MAFF) began to kill badgers in areas where it was judged that they posed a threat to the health of cattle. This policy was highly controversial. Firstly, because the role of badgers in transmitting TB to cattle was not conclusive, and secondly because the badger is a protected species, and in addition many people considered the method of killing, using poison gas, to be unacceptable. Although gassing of badgers was subsequently halted on humane grounds, the effects of mass culling of badgers on the incidence of TB in cattle was monitored in some detail in certain areas. It was found that the number of cases of TB in cattle fell sharply during and after the badger-removal period, but eventually started to increase again after the culling of badgers was stopped. This was further evidence that TB infection in badgers plays a significant role in the spread of the disease to cattle.
Thats from here if you want to read it all:
http://www.nimr.mrc.ac.uk/mill-hill-essays/tuberculosis-in-man-cattle-and-badgers