INDUSTRY SUMMARY

The goal of this research was to develop easily measurable parameters for assessing conditions that would eliminate or reduce potentially pathogenic bacteria in stacked poultry litter. The temperature profile i.e., changes in temperature over time and the physical parameters, water activity (Aw), pH, and moisture content (% dry matter, DM) were intensively monitored for 6, five to 8 ton stacks of poultry litter from broiler chicken facilities. Piles were not turned or aerated after being delivered and instrumented with continuous temperature probes. In addition to continuous probes, manual temperatures were recorded daily at 1 foot to 5 foot depths at a height of 2' from the base of the pile (ground level). The survival of 3 bacteria, Campylobacter, Escherichia coli and Salmonella, bacteria that are also of food safety concern for humans, was measured in 3 piles. From the raw data we generated two predictive models to look at, 1) the effect of the pile on the temperature profile (i.e. changes in temperature over time), and 2) the effect of the physical parameters measured (pH, water activity (Aw), % moisture (DM)) on the temperature profile of the pile. The majority (5/6) of piles reached similar average temperatures (120-155 F), but one pile that was dryer and contained less manure, was cooler on arrival and throughout the testing period. Individual points within piles reached temperatures greater than 170 F. Piles originating from different locations showed a uniform and parallel increase in temperature over time, when measured at a fixed depth and height, 36" and 12", respectively. Temperatures peaked between 2 and 10 days after stacking and declined slowly over the next 10 days. Measuring the pile at incremental depths and heights revealed that areas near the surface heat more rapidly than the deeper portions of the pile. The maximum temperatures generated in the deeper portions of the pile (5' depths) occurred 5 to 7 days after stacking. Also positively correlated with temperature was the height of the measurement from the base of the pile. Temperatures measured near ground level were approximately 5 degrees cooler than temperatures measured at a height of 3 feet from the base of the pile at any point in time (with depth held constant at 3 feet). This means that minimal "safe" temperatures, those necessary to kill microbial pathogens, are depth dependent and guidelines would need to specify the time since stacking and the height and depth at which the measurements should be made. The pH of the litter piles increased for 7 to 10 days after stacking, then decreased, probably due to early volatilization of nitrogen as ammonia. Litter piles with high pH (basic) generated more heat than acidic piles. A 5 C difference was observed between piles with neutral to acidic pH versus those with basic pH at any point in time. Based on this data, litter treatments that lower pH may also affect the heating process of stacked litter. The parameter with the greatest single influence on the temperature profile of stacked poultry litter in our model was Aw. Our model predicts that litter piles with higher Aw will be 20 C hotter than those with low water activity. Thus a producer could adjust the moisture of poultry litter before stacking to improve heating. Bacterial survival in stacked litter was poor. The maximum time after inoculation that bacteria was recovered was 2 h for Campylobacter, 32 h for E. coli and 28 h for Salmonella. Given the sensitivity of our testing these data roughly correspond to a 4 to 6 log reduction in Salmonella within 28 h; a 5 log reduction in E. coli within 32 h, and a 2 to 3 log reduction in Campylobacter in 2 h p.i. The information from this study should be useful to poultry growers that wish to develop on-farm, good management practices for microbial safety of stacked poultry litter. In addition, this information can be used as a marketing tool for producers supplying litter for crop application and could be invaluable in guiding the formulation or revision of regulatory policies for agricultural use of poultry litter.