Purpose: To evaluate possible associations between on-farm management practices and levels of psychrotolerant sporeformers in bulk tank milk.
Methods: One bulk tank sample was obtained and a management/herd health questionnaire was administered to 99 New York State dairy farms. Milk samples were spore pasteurized (SP) (80°C (176°F), 12 min) and analyzed for most probable number and for sporeformer counts on initial day of SP, and after refrigerated storage (6°C) at 7, 14, and 21 d post-SP. Management practices were analyzed for association with sporeformer counts and bulk tank somatic cell counts, respectively. Select isolates were characterized by partial rpoB gene amplification, sequencing, and allelic type assignment.
Results: Sixty-two farms had ‘high’ sporeformer growth ( ≥ 3 log CFU/ml at any day post-SP) with an average sporeformer count of 5.20 ± 1.41 mean log CFU/ml at 21 d post-SP. Thirty-seven farms had ‘low’ sporeformer numbers ( < 3 log CFU/ml for all days post-SP) with an average sporeformer count of 0.75 ± 0.94 mean log CFU/ml at 21d post-SP. The percent of milking cows with dirty udders in the milking parlor and herd size were significantly associated with farms that had ‘high’ sporeformer growth. The majority of isolates characterized represented either Bacillus spp. (71.4%; 317/44) or Paenibacillus spp. (26.4%; 117/444).
Significance: On-farm adjustments in management decisions specifically focused on udder cleanliness may directly impact the shelf-life of pasteurized fluid milk.