Effect of unvaccinated Merino wether lambs on shedding of Mycobacterium avium subspecies paratuberculosis in flocks vaccinating for ovine Johne's disease

TM for at least 5 years, but had not vaccinated their last two drops of wethers were studied. Faecal samples were collected in pools of 50 from 350 vaccinated ewes (1–2 years old) and from 350 unvaccinated wethers of the same age and were cultured to determine the presence of viable Mptb. Results The estimated prevalence of shedding sheep among the unvaccinated wethers was 6-fold greater than among the vaccinated female siblings (0.21% vs 1.27%), with faecal pools collected from unvaccinated wethers being 19-fold more likely to be positive than those from the vaccinated ewes.