Microbial Characteristics and Safety of Dairy Manure ComPosting for Reuse as Dairy Bedding

SIMPLE SUMMARY: The cost of cow manure treatment and bedding increases the operating cost of the ranch. Many ranches fill out the recycled manure solids (RMS) process to dry manure as bedding material. However, the microbial safety of RMS bedding is still uncertain, and the change of microbial diversity of the feces after each processing step is not clear. In this study, an amplified fragment sequence was utilized to analyze the microbial flora, bacterial phenotype, and metabolic function prediction of the products in the process of RMS processing. At the same time, samples of sand soil bedding material, rice husk bedding material and RMS bedding material were compared and analyzed. The results will be useful to further study the safety of RMS padding to reduce the operation cost of dairy farms and the incidence rate of mastitis. ABSTRACT: Changes in bacterial community, phenotype, metabolic function, and pathogenic bacteria content in recycled manure solids (RMS) were analyzed by 16S rRNA sequencing, Bugbase, picrost2, and qPCR, respectively. The data from RMS bedding were compared to those of sand bedding and rice husk bedding. The results show that the proportion of potentially pathogenic bacteria among the manure flora of RMS after dry and wet separation, after composting, and after sun-cure storage was 74.00%, 26.03%, and 49.067%, respectively. Compared to RMS bedding, the proportion of potentially pathogenic microorganisms in sand bedding and rice husk bedding was higher. The picrust2 analyses show that the level of lipopolysaccharide biosynthesis changed significantly during RMS processing. In addition, the qPCR results show that composting could effectively reduce the detection and quantification of pathogens, except Streptococcus uberis, in RMS bedding. In general, composting is an essential step to improve the safety of bedding materials in the process of fecal treatment. However, at the same time, RMS bedding may increase the risk of mastitis caused by Streptococcus uberis.