RELATION BETWEEN MILK PRODUCTION CONDITIONS AND RESULTS OF BACTERIOLOGICAL TESTS WITH AND WITHOUT PRELIMINARY INCUBATION OF SAMPLES1

Abstract

Summary The effectiveness of various bacteriological methods in detecting insanitary production conditions was studied over a two-year period at three centers. It had been planned to use the pulsating rinse test as a yardstick, but it was found necessary to supplement this with a weighted scoring system for “faults” reported on inspection. Farms were classified as satisfactory or unsatisfactory on this basis. In contrast to previous experience, preliminary incubation (PI) at 55 F for 18 hr failed to show any significant advantage. However, subsequent studies revealed that results would have been more favorable had samples been taken from full tanks, rather than of the first two milkings. Results varied markedly between the three centers in the degree to which unsatisfactory conditions were reflected by both standard plate counts (SPC) and resazurin reduction tests. Resazurin reduction times equivalent to various SPCs varied strikingly from center to center, and even between two groups of farms at a given center. All were appreciably greater than those currently in vogue. Bacteriological standards as stiff as 10,000/ml SPC failed to detect up to 32% of farms scored as unsatisfactory, emphasizing anew the importance of regular, frequent, careful inspection of farms.