Development of a controlled laboratory model for studying compost bedded pack systems and microbial dynamics

This study aimed to develop a compost bedded pack (CBP) model of the active composting layer in dairy housing systems by applying conditions observed on commercial CBP farms along with parameters from published studies. The model was constructed using pack materials collected from 4 commercial CBPs, managed under standardized laboratory conditions to minimize environmental variability. Compost bedded pack material consisting of manure and sawdust obtained from each farm was divided into 6 containers with 3 randomly assigned to control (daily mixing only) and 3 randomly assigned to enriched (daily mixing and manure addition, weekly addition of sawdust). A total of 24 composting containers (n = 24; 6 containers from each of 4 source CBP packs) were managed for 5 weeks. Data were analyzed using a repeated-measures mixed model with treatment, week, and their interaction as fixed effects. The CBP model was assessed by measuring temperature, moisture content, carbon-to-nitrogen ratio, and the levels of cellulose, hemicellulose, and lignin for each container. The enriched treatment supported sustained physicochemical changes consistent with composting processes, as temperature increased from 30.2°C in wk 1 to 40.0°C in wk 5. In contrast, temperatures in the control containers declined from 24.8°C in wk 1 to 22.6°C in wk 5. Moisture in the enriched group remained within optimal composting levels (58.6 - 61.6%), whereas the control showed moisture loss (56.73 - 36.42%). The C:N ratio in the enriched group declined from 28.6 to 16.8 from wk 1 to 5, and overall cellulose content decreased by 26.9% despite weekly sawdust additions. This amount was calculated from data of the ratio of average sawdust addition to manure deposited in summer months on Ontario commercial packs that maintained a temperature above 42°C and between 40% and 65% moisture. The hemicellulose and lignin content did not differ significantly over time even though sawdust was added weekly, suggesting ongoing decomposition. Microbial profiling revealed that Bacillota, Bacteroidota, Pseudomonadota, Actinomycetota, and Verrucomicrobiota were the dominant phyla in both enriched and control containers. Among these, Bacillota, Bacteroidota, and Actinomycetota were detected in 100% of samples at a relative abundance of ≥ 1% and were thus defined as the core phyla. Overall, the laboratory CBP model successfully replicated active composting dynamics and offers a safe and controlled platform for future studies of pathogen survival.