Persistence of Mycobacterium avium subsp. paratuberculosis and Other Zoonotic Pathogens during Simulated Composting, Manure Packing, and Liquid Storage of Dairy Manure

Livestock manures contain numerous microorganisms which can infect humans and/or animals, such as Escherichia coli O157:H7, Listeria monocytogenes, Salmonella spp., and Mycobacterium avium subsp. paratuberculosis (Mycobacterium paratuberculosis). The effects of commonly used manure treatments on the persistence of these pathogens have rarely been compared. The objective of this study was to compare the persistence of artificially inoculated M. paratuberculosis, as well as other naturally occurring pathogens, during the treatment of dairy manure under conditions that simulate three commonly used manure management methods: thermophilic composting at 55°C, manure packing at 25°C (or low-temperature composting), and liquid lagoon storage. Straw and sawdust amendments used for composting and packing were also compared. Manure was obtained from a large Ohio free-stall dairy herd and was inoculated with M. paratuberculosis at 10⁶ CFU/g in the final mixes. For compost and pack treatments, this manure was amended with sawdust or straw to provide an optimal moisture content (60%) for composting for 56 days. To simulate liquid storage, water was added to the manure (to simulate liquid flushing and storage) and the slurry was placed in triplicate covered 4-liter Erlenmeyer flasks, incubated under ambient conditions for 175 days. The treatments were sampled on days 0, 3, 7, 14, 28, and 56 for the detection of pathogens. The persistence of M. paratuberculosis was also assessed by a PCR hybridization assay. After 56 days of composting, from 45 to 60% of the carbon in the compost treatments was converted to CO₂, while no significant change in carbon content was observed in the liquid slurry. Escherichia coli, Salmonella, and Listeria were all detected in the manure and all of the treatments on day 0. After 3 days of composting at 55°C, none of these organisms were detectable. In liquid manure and pack treatments, some of these microorganisms were detectable up to 28 days. M. paratuberculosis was detected by standard culture only on day 0 in all the treatments, but was undetectable in any treatment at 3 and 7 days. On days 14, 28, and 56, M. paratuberculosis was detected in the liquid storage treatment but remained undetectable in the compost and pack treatments. However, M. paratuberculosis DNA was detectable through day 56 in all treatments and up to day 175 in liquid storage treatments. Taken together, the results indicate that high-temperature composting is more effective than pack storage or liquid storage of manure in reducing these pathogens in dairy manure. Therefore, thermophilic composting is recommended for treatment of manures destined for pathogen-sensitive environments such as those for vegetable production, residential gardening, or application to rapidly draining fields.