Effects of silage fermentation and ammonia treatment on activity of Mycobacterium avium subsp. paratuberculosis

It was confirmed in a previous paper that M.avium subsp.paratuberculosis was killed when kept in a high moisture silo with low pH value and high lactic acid content. In the present paper, effects of storage on survivabiiity of M.avium subsp.paratuberculosis in low moisture- or ammonia- treated silages containing less organic acid and having a high pH were investigated in 2 kinds of pouched silages. Pouch silos containing sterilized ground alfalfa hay and a piece of filter paper onto which M.avium subsp. paratuberculosis suspension had been applied were made at moisture levels of 75, 60, 45, 30 or 10%, with lactic acid bacteria added at the time of ensiling. The other pouch silos containing the same materials were made with 30% moisture, and 1 or 3% ammonia added at ensilaging. Though the count of M.avium sub sp.paratuberculosis in the pouch silos with moisture of 60% or more, low pH and containing high lactic acid decreased below the detectable level, bacteria in pouch with 45% moisture or below, containing less lactic acid with a higher pH survived after 14 days incubation at 30 deg C. However, the count of M.avium subsp.paratuberculosis in the pouch treated with 3% ammonia decreased below the detectable level, while in the pouch treated with 1% ammonia, it also decreased and some bacteria survived. The above results suggest that low moisture silage, hay and roughage treated with 1% ammonia made from grass or forage crop that are contaminated with M.avium subsp.paratuberculosis, might be a cause of Johnes' disease. When grass or a forage crop possibly contaminated with M.avium subsp.paratuberculosis must be fed, it is suggested that it should be stored as high moisture silage at low pH with added formic acid, or low moisture roughage treated with more than 3% ammonia.