Aim:  The pathogen growth in dairy compost was studied in a greenhouse setting under different seasons. Methods and Results:  The five‐strain mixtures of each Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes were inoculated separately into dry compost to yield c. 1 log CFU g−1. After acclimation at room temperature, the inoculated compost was initially adjusted to moisture levels of 10–50% and then kept in a greenhouse under different seasons. The populations of all three pathogens increased by 2·1–3·9 log CFU g−1 within 3 days in autoclaved compost with initial moisture content of at least 40%. Listeria monocytogenes multiplied up to 2·4 log CFU g−1 in compost with initial moisture content of 30% and was detected up to 28 days for all seasons, whereas populations of both E. coli O157:H7 and Salmonella increased by c. 1 log in compost with initial moisture content of 30% during winter months only. No pathogen growth in nonautoclaved compost was detected. Conclusion:  Bacterial species, temperature, light intensity and moisture content affected the growth potential and survival of pathogens in compost when the population of background microflora was low. Significance and Impact of the Study:  Keeping compost as dry as possible and maintaining certain levels of background microflora may be critical to prevent the growth of pathogens.

Our results have provided scientific data on the pathogen survival in dairy and poultry composts, which could be used for the risk assessment of using animal waste-based composts as biological soil amendments.