M. bovis can Survive on Salt Blocks

Researchers and veterinarians have long known that bovine tuberculosis (TB) can spread between cattle, or from wildlife to cattle, through feed sources. Researchers at Michigan State University now have confirmed that Mycobacterium bovis, the primary pathogen associated with bovine TB, can survive for up to three days on salt or mineral blocks.

The researchers, from MSU’s College of Veterinary Medicine, Center for Comparative Epidemiology, inoculated salt blocks and salt-mineral blocks, with M. bovis over two 12-day periods during the summer and winter, using a strain currently circulating in Michigan livestock and wildlife. They placed some blocks in the shade and some in sunlight, then collected and cultured samples from the block surfaces beginning within one hour after placement, twice a day for the first four days and once a day from days seven through 11.

Their results indicate that while environmental conditions affect survival of the pathogen, M. bovis can survive on salt or mineral blocks. The researchers found viable M. bovis for up to two days on salt blocks and for more than three days on salt-mineral blocks. The odds of finding the pathogen on the blocks were almost five times as high during the winter as during the summer and three times as high when the block was in the shade compared with blocks exposed to sunlight.

The researchers concluded that salt or mineral blocks can act as sources for spreading bovine TB, especially in areas where wildlife populations serve as reservoirs for M. bovis.

The research results are published in the American Journal of Veterinary Research.