Investigation of Factors Contributing to the Bacterial Count of Bulk-Tank Milk. I. Influence of Two-Day Storage and Effect on Results of Preliminary Incubation

The effect, on the standard plate count of milk, of storage in the bulk-tank with alternate-day collection was investigated using samples from 48 farms drawn from three widely separated regions in Canada.On the whole, preliminary incubation had a greater effect on the counts o£ milk that had been stored under refrigeration than on those of nnstored milk.Storage in the tank gave slightly higher counts after incubation than did storage at constant temperature in the laboratory, but not enough to represent a major factor in the effect of preliminary incubation.A series of collaborative studies was made, between 1961 and 1964, on the detection of unsanitary conditions of production by bacteriological tests on milk from refrigerated bulk-tanks.Some of the findings of the work, which was done at the Universities of Alberta (Edmonton), Manitoba (Winnipeg), and Guelph (Ontario), have been reported (4).The results of those studies, and the problems of their interpretation and application, showed a need for more information on certain points.A further collaborative study was, therefore, initiated in an endeavor to trace the build-up of bacteria in milk, from milking of the cows until alternate-day tanker collection.The ef-