Low-dose BCG vaccination protects free-ranging cattle against naturally-acquired bovine tuberculosis.

•BCG vaccine was trialled in New Zealand cattle against naturally-acquired bovine TB.•We applied a five-fold lower BCG dose to cattle than any previously-used in cattle.•Annual TB prevalence was low (<4%); nevertheless vaccine efficacy was significant (87.5%).•Reduced BCG doses could favour cost-effective use of the vaccine in farming.