Spatial variability of heating profiles in windrowed poultry litter

In-house windrow composting of broiler litter has been suggested as a means to reduce microbial populations between flocks. Published time-temperature goals are used to determine the success of the composting process for microbial reductions. Spatial and temporal density of temperature measurement can influence the accuracy in determining what portion of a windrow section has achieved specified time-temperature goals. In this study, windrow section temperature was recorded every 2 min for 7 d on a 10 × 10-cm grid in 183 (width) × 91 cm (height) windrow sections. In 5 windrow sections, ordinary kriging was used to predict the mean portion of the windrow cross-sectional area reaching time-temperature goals of 40°C for 120 h, 50°C for 24 h, and 55°C for 4 h. Based on these results, 88.5 ± 2.0%, 80.8 ± 3.9%, and 38.4 ± 11.7% of the windrow cross-sectional area can be expected to reach published microbial reduction time-temperature goals of 40°C for 120 h, 50°C for 24 h, and 55°C for 4 h, respectively. This study illustrates the need to monitor temperature at multiple locations within windrowed litter to characterize heating profiles. Temporal and spatial sampling densities must be standardized to properly characterize temperature profiles in windrowed broiler litter. Additional research should be conducted to determine the degree of pathogen destruction achieved in the various time-temperature regions of the windrow pile. This study was useful in illustrating the efficacy (proportion of windrow cross-section) of windrow composting as a treatment method for reducing microbial populations as measured by time-temperature goals in used broiler litter.