Butyric acid-producing bacterial spore levels in conventional raw milk vary by farm

Anaerobic butyric acid-producing sporeforming bacteria (BAB) are important microbial contaminants in raw milk that may lead to premature spoilage of certain cheeses during aging. A study was conducted to determine the baseline levels of these spores in raw milk from 7 conventional Northeast United States dairy farms over a 1-yr period. The overall mean BAB concentration was 1.79 log₁₀ most probable number per liter with spore levels differing significantly by farm. A post-hoc farm management practices survey was conducted to determine if there was an association between farm practices on BAB levels in raw milk from these farms. Survey questions included variables related to bedding, milking preparation procedures, teat and udder cleanliness scoring, holding area cleaning procedures, and udder clipping or flaming frequency. Each variable was fitted with a linear mixed-effects model, which revealed no significant association between farm-level factors and the initial BAB concentrations in raw milk; this finding was likely due to the small sample size in this study. To demonstrate the usefulness of our data beyond the initial baseline levels of BAB spores in raw milk, we used this data set to calculate minimum number of individual samples that would be needed to be collected in future studies, which was determined to be 96 to 126 samples, to evaluate the association between farm-level factors and BAB spore concentrations in raw milk. Overall, this study provides dairy industry stakeholders with baseline data on BAB spore levels in raw milk, along with a demonstration on how these data could be used in future studies to calculate sample sizes needed to assess the effect of farm management practices on BAB levels in raw milk.