There is anecdotal evidence that some breeds of sheep and cattle differ in their susceptibility to Johne’s disease. We have recently completed a trial to examine differences in susceptibility between four breeds of sheep: Merino, Border Leicester, Poll Dorset and first-cross Suffolk x Merino lambs. We found that all the breeds studied developed infection and became clinically diseased. However, there was a big difference in the number of animals from each breed that developed clinical disease by the end of the trial. Another major finding from this study was that while many sheep became infected disease was not visible in many of them.