Factors associated with coliform count in unpasteurized bulk milk
Abstract: The objective of this study was to identify factors associated with bulk milk coliform count. Dairy farms (n=10) were visited once weekly on sequential weekdays over a period of 10 wk. During each visit, in-line drip samplers were used to collect 1 milk sample from 2 points of the milk line (between the receiver jar and milk filters, and after the plate cooler). During the same period that in-line milk samples were collected, university personnel observed milking performance and hygiene and collected liner (n=40) and teat skin swabs (n=40). For all milk samples (n=181), geometric mean in-line milk coliform count was 37cfu/mL. In-line milk coliform count varied by farm, ranging from 5 to 1,198cfu/mL. In-line milk coliform counts were 4 times greater (115 cfu/mL) when milking machine wash failures occurred compared with in-line milk coliform counts after normal washes (26 cfu/mL). Geometric mean in-line coliform count (cfu/mL) increased 6.3% for every 10% increase in in-line milk somatic cell count (cells/mL). Results of this study provide novel information about farm factors associated with coliform counts, as estimated in milk before storage in tankers or bulk tanks, and highlight the importance of proper and consistent milking machine washes in minimizing bulk milk coliform contamination. The nature of the associations between liner coliform counts, rate of cluster washes, rate of milking units fall-offs, and in-line coliform counts indicates that managing and monitoring such events has the potential for improving bacteriological quality of farm bulk milk.