An Evaluation of Raw Milk Microorganisms as Markers of On-Farm Hygiene Practices Related to Milking

Abstract

Dairy farm hygiene audits were undertaken at 24 farms during summer and winter and the results compared with transformed bacterial indicator levels in raw milk samples collected during each audit. The bacterial indicators measured were total viable counts, Escherichia coli, coliforms, Bacillus spp., Bifidobacteria spp., and Pseudomonas spp. The results of initial comparisons using Pearson product-moment correlation coefficients showed presumptive relationships between some bacterial groups and the subjective quantitative audit scores. When investigated further using linear regression, the presumptive relationships were found to be influenced by external factors. Possible reasons for the low correlations between on-farm hygiene and bacterial indicator counts in raw milk were further investigated. Measurements of the uncertainty associated with the bacteriological results were undertaken and revealed geometric relative standard deviations that ranged from 0.019 to 1.05. Toward the higher end of this scale, the uncertainty associated with the laboratory estimations of bacterial numbers may have been large enough to blur hygiene score-marker bacteria relationships. The samples obtained from on-farm raw milk storage tanks were representative of the whole tank contents and not a significant source of error. Although total bacterial counts are widely acknowledged by the milk industry as not always giving a true measure of on-farm hygiene during milking, we were unable to find any marker bacteria that showed consistently higher correlations and were thus better suited as indicators of on-farm hygiene.

Effect of pre-milking teat preparation procedures on the microbial count on teats prior to cluster application

“…There is strong evidence that among all pre-milking procedures, wet cleaning treatment, followed by paper towel manual drying will result in the lowest bacterial counts [4,6,17,7]: this practice is particularly effective in reducing milk bacterial contamination during the winter housing period [17]. Similar seasonal bacterial infection trends linked to the pasturing/housing routine have been observed by Hutchison et al [11]. …”

“…The losses associated with mastitis include discarded milk, increased number of culled cows, cost of antibiotic treatment and reduced milk quality and price [11,13]. Even though, it has been shown that factors such as genetic characteristics, impaired immune-function, feeding regimes [20] and machine milking [22,1] are related to mastitis, poor milking hygiene has been associated with increased somatic cell count (SCC), reduced milk production and inferior milk quality [12,18,20].…”

“…Machine milking may also be considered as a major cause of bacterial cross contamination from cow to cow. However, a good premilking hygiene routine can decrease the cow infection ratio by not only reducing udder bacterial contamination from the environment, but also reducing bacterial contamination from other infected animals [9,12,11]. Newbould [21].…”

Fluid Milk and Cream Products

“…Milk handling on the farm results in further contamination and growth of spoilage organisms. Sources of microbiological contamination on the farm include equipment used for automated milking, milk handling lines, and refrigerated bulk milk storage tanks (Polyanskii et al, 2005;Hutchinson et al, 2005). Psychrophilic bacteria (i.e., the genus Pseudomonas sp.)…”

“…The end products of bacterial growth that are responsible for this highly objectionable off-flavor may be produced either (1) directly by the bacteria when they grow in the milk or (2) indirectly when they grow on improperly cleaned equipment surfaces from which they are transferred into the milk. Spoilage by psychrophilic bacteria has been the subject of numerous studies (e.g., Bodyfelt, 1974Bodyfelt, , 1980aBodyfelt, , 1980bBradley, 1983;Hankin and Anderson, 1969;Hankin and Stephans, 1972;Hankin et al, 1977;Mikolajcik and Simon, 1978;Polyanskii et al, 2005;Hutchinson et al, 2005).…”