Inspections are an inevitable part of the routine on most dairy farms. The demand for a safe, high quality product is driven, in part, by consumers who put pressure on producers for transparency and adherence to safety standards. Processors also require a product that consistently meets their standards resulting in the production of a high quality, uniform product on a regular basis. Producers in turn, may be rewarded with premiums for meeting quality standards. But do these inspections correlate with the quality of milk that is being shipped?

Do audits correspond with microbiological milk quality indicators 

Previous research has demonstrated mixed results to this question. Recently, a group of researchers in the Netherlands revisited this topic. The researchers sought to correlate farm audits with the microbiological measure of total bacterial counts (TBC; Flores-Miyamoto et al., 2014). The TBC is determined using a piece of laboratory equipment that directly counts the bacteria present in a sample of raw milk. The analysis is completed within a matter of minutes. Direct counting methods are different from traditional culture-based methods because both viable and non-viable bacteria are counted, whereas culturing only provides a count of viable bacteria in a sample.

The audits conducted in this study included the use of veterinary drugs, animal health, equipment, facilities, personnel and farm hygiene, disinfection procedures, residues, and management of feed and water. Data from over 13,000 farm audits were examined with a goal of quantifying a microbial measure of bulk tank milk with audit results. TBC were determined twice a month for a period encompassing 6 months prior to the audit through 6 months following the audit. Producers received notice 2 to 5 days before the audit was conducted. 

The results of this study demonstrated a statistically significant difference with the 10 TBC samples taken from 1.5 to 6 months following the audit when compared to the values from a sample taken at the time of the audit. The researchers suspected the observed lag was due to a delay in receipt of audit results from 3 to 6 weeks after the audit. On average, the number of bacteria decreased by 6% after the audit. Farms that had unfavorable audit results generally had higher TBC than farms that were approved during audits. Other observed variations were related to seasons and maintenance of milking equipment and utility room-tank. Overall, if an audit provided a negative assessment, then TBC were higher. The researchers indicated that audits provide additional information on milk quality for producers, but the information may be limited. 

Similar studies previously have been conducted in the United Kingdom (Hutchinson et al., 2005) and in the United States (Ingham et al., 2010). The study conducted in the United Kingdom included 24 farms with audits conducted during the summer and follow-up during the winter. Bacteria counts were monitored prior to the audit to ensure that the farms selected for the study had stable counts. A sample was taken at the time of the audit then 3 additional visits were made to collect a total of 20 additional samples. Microbiological measures included total viable counts, Escherichia coli, coliforms, and 3 other bacterial indicators. The researchers were not able to draw consistent conclusions that any of the bacterial indicators examined provided a better representation of hygienic practices on the farms than total viable counts when compared to the audits.

The study conducted in the United States (Ingham et al., 2010) relied on data collected from more than 11,000 grade A dairy farms in Wisconsin. The researchers sought to correlate farm inspection reports with laboratory somatic cell counts (SCC), standard plate counts (SPC), and β-lactam drug residue (DR) results for the farms. The farm inspections included evaluation of the cleanliness of cows, the milk house, and the barn, examination of the water supply, waste disposal, plumbing, and pest control, the sanitation and condition of milking equipment, the temperature of the bulk tank, and the use and storage of veterinary pharmaceuticals. Data were analyzed several ways including by transforming the microbiological indicators and the inspections to indicate “pass” or “fail.” None of the variables demonstrated a strong correlation with inspection results. Farms that typically shipped milk that passed SCC, SPC, and DR requirements were unlikely to fail an inspection. An issue with SCC, SPC, or DR was only weakly reflective of problems observed during an inspection.   

Farm audits or inspections serve a clear and meaningful purpose as does the microbiological examination of bulk tank milk samples. However, the research that has been conducted to date does not appear to define a clear relationship between these useful management tools. As new technologies and tools emerge for examining milk quality so may a microbiological indicator with a clear link to inspections or audits.