Pathogen re-colonization of in-house composted and non-composted broiler litter

Authors: Brooks, John; McLaughlin, Michael; Adeli, Ardeshir; Miles, Dana

Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2015
Publication Date: 6/15/2015
Publication URL: https://handle.nal.usda.gov/10113/62579
Citation: Brooks, J.P., Mclaughlin, M.R., Adeli, A., Miles, D.M. 2015. Pathogen re-colonization of in-house composted and non-composted broiler litter. Journal of Applied Poultry Research. 24:157–167. doi.org/10.3382/japr/pfv013.

Interpretive Summary: In-house composting of broiler litter is an effective method to reduce pathogenic bacteria in litter which can otherwise lead to diseased birds or foodborne contamination. This method of composting is based on allowing good bacteria to create heat in a static pile which will generate ammonia and subsequently kill off the pathogenic bacteria. While this approach is quite useful, there is potential for re-colonization of pathogens once the temperature goes down or when the birds are reintroduced. This potential is related to indiscriminate killing of many other good bacteria during the heating process; these good bacteria occupy certain niches which when removed from the niche, allows for the colonization of pathogens. This study simulated the heating of composting and potential for recolonization of pathogens in broiler litter. The study was simulated over a single flock period with pathogens inoculated into the litter, thus allowing for potential colonization. The study demonstrated that composted litter was more susceptible in the early periods of the flock, which most likely was due to a less complex microbial population, which confirmed the hypothesis. Growers can continue to use in-house composting, however, caution should be taken during the initial weeks of the flock cycle during which pathogens can recolonize more readily.

Technical Abstract: “In-house” litter composting has been reintroduced to the industry and shown to reduce bacteria by as much as two orders of magnitude. Other industries have demonstrated that pathogens can recolonize a waste-residual when microbial competition has been reduced or inhibited following composting. Poultry growers, in the process of shifting to in-house composting for pathogen control, should be aware of this potential problem. In-house composting of litter has not become an industry wide standard; however, prior to its full adoption, this potential caveat should be investigated. A laboratory microcosm study investigated pathogenic bacteria re-colonization into composted and non-composted broiler litter over a simulated broiler “grow out” cycle. Objectives were to: 1) determine colonization rates for human and poultry bacterial pathogens; 2) identify beneficial bacteria which reduce pathogen re-colonization; and 3) identify the effects of ammonia on pathogen re-colonization. Composted broiler litter allowed foodborne pathogens to colonize at a slightly faster rate within the first two weeks of the “grow-out” period when compared to non-composted. Colonization was nearly identical by the end of the “grow-out” period, and showed that bacterial pathogens had essentially been overtaken by commensal or normal bacteria. DNA identifications demonstrated reductions in Proteobacteria associated with composted litter, which may indicate that this type of bacteria was necessary to reduce initial colonization. Ammonia generation did not inhibit or promote bacterial colonization, as levels were high for both litter treatments and no differences could be attributed to ammonia. This study neither suggested nor condemned the continued use of this cost-effective, litter-treatment process; findings suggest that while the “good” microbial population was initially reduced, it quickly recovered and pathogen colonization was neither enhanced nor inhibited because of this. This study demonstrates that the recently adopted in-house composting process may continue to be used, provided poultry health gains continue to be seen.