The Microflora of Milk Drawn Aseptically from the U.S.A.C. Dairy Herd

Early studies on the bacterial content of milk were made mainly to satisfy the interest of people who wished to determine the various materials that contained bacteris. Soon the value of bacterial counts, as an indication of the general conditions of production, of handling, and of the keeping qualities of milk, became evident and bacterial counts were used to obtain information concerning these problems. Numbers of bacteria in milk have been used also in the studies of the desirable and undesirable changes in milk. In the last few years our citizenry has been made more conscious of the presence and importance of bacteria in milk. As the number of milk dealers have increased and our population in the cities has become more conjested, more stringent regulation of our milk supplies has been practiced. Of major importance in this regulatory program is the bacterial count of milk. Large dairy manufacturing plants, which have also recognized the importance of high bacterial counts in influencing the quality of their products, have encouraged production of low count milk even to the extent of giving bonuses to such producers and rejecting milk that did not come within their standards. It is a well recognized fact that the producer may control the bacterial content of milk which results from external contamination, but what about the contamination coming from the interior of the udder? Not as much attention has been paid to the latter problem as to the former. From the standpoint of ordinary market milk from healthy cows, the intermal contamination does not assume much importance but to the producer of low count milk, and especially certified milk with its common standard of 10,000 bacteria per cc., this problem of interior contamination from the udder may become of major importance. Some cows with apparently normal udders have been known to consistently give milk of high bacterial content. Some of these examples may be noted by studying cases quoted in the historical section of this thesis (14). In some instances the failure of certified milk to come up to the bacteriological requirements has been due to a few cows giving exceptionally high count milk. The exclusion of this milk has immediately brought the number of organisms within the required limits (11).* In this investigation a study has been made of the normal number of bacteria in milk aseptically drawn from apparently normal cows of the Utah State Agricultural College dairy herd. In other words, in this herd what is the count of bacteria that is unavoidable, even with the greatest care in milking? Does the number of bacteria in the udders vary from month to month? Does the number between cows vary and is there a significant variation between quarters? Are there certain cows that consistently produce milk of low count? From this information it should be possible to predict the quality of milk, high or low count, the cow will produce. What types of bacteria occur in the udder? Is this flora constant or does it vary