Preservation and Storage Mechanisms for Raw Milk Samples for Use in Milk-Recording Schemes.

This study, carried out by the Quebec Dairy Herd Analysis Service, compares (during summer conditions in Quebec) the performance of three types of preservatives for raw milk under four different systems of sample storage: no refrigeration, refrigeration at the laboratory only, refrigeration during transport and at the lab, and complete refrigeration from sampling at the farm to analysis. The objective was to determine the best preservative and storage conditions for protecting milk components during transportation and storage of raw milk samples collected at the farm and sent to a central testing lab for analysis. Milk samples were analyzed at day 3 and at day 7 after sampling to observe the effect of aging. A total of 12,480 samples were collected during the trial. The components studied were percentage of fat and protein and somatic cell count (SCC). In general, samples preserved with bronopol (2-bromo-2-nitropropane-1,3-diol and 2-bromo-2-nitropropanol) in liquid or in microtab tended to give higher readings for fat and protein contents than samples preserved with potassium dichromate. Significantly lower fat values were observed in 7-day-old samples compared to 3-day-old samples. Fat depression was more accentuated in nonrefrigerated samples. Under current methods of handling raw milk samples, refrigeration during the whole process of sampling, transportation, and until analysis, seems an ideal to attain to avoid significant reductions of fat values.