This email received May 30th 2015 from a Wiltshire farmer.
My understanding of the situation is that the skin test for tb simply asks the question - has the animal met mycobacterium bovis, and provides a straight yes or no answer. The question of the animal's susceptibility does not enter into it. I have heard it suggested that where maize is available for badgers a larger than usual proportion of cubs survive into adulthood, contributing to overcrowding in the set, and where tb is present hastening its spread. I am not able to say whether the mineral content of the maize makes the badgers more susceptible or not.