Methods of processing recycled manure solids bedding on Midwest dairy farms I: Associations with bedding bacteria counts, milk quality, udder health and milk production

This observational study investigated the relationships between method of processing recycled manure solids (RMS) bedding and 1) bacteria counts in RMS bedding, 2) bacteria counts in bulk tank milk, and 3) udder health and milk production. A convenience sample of 29 farms in Minnesota and Wisconsin were recruited to represent 4 RMS processing systems; green (GRN, n = 7), anaerobic digestion (DIG, n = 6), composting (COM, n = 4), and hot air drying (DRY, n = 12). Premises were visited twice (summer/winter) to collect fresh bedding and bulk tank milk (BTM) samples for culture, test day records, and a herd management questionnaire. Coliform and Klebsiella spp. counts were lower, or tended to be lower in DRY, COM or DIG versus GRN RMS samples. Counts of Streptococci and Strep-like organisms (SSLO) were statistically or numerically lower in COM or DRY as compared to GRN or DIG RMS samples. Coliform and SSLO counts in BTM were lower, or tended to be lower, in DIG, COM or DRY as compared to GRN RMS samples. Test-day average linear score, proportion of cows with infection, and proportion of cows with chronic infection was lower, or tended to be lower, in herds using DRY or COM versus GRN RMS bedding. Average 305ME was higher, or tended to be higher, for herds using DRY versus GRN or DIG RMS. Adoption of COM or DRY processing could allow producers to mitigate the negative impacts of high bacteria levels in GRN RMS bedding, though more research is needed.