Methods for Studying Factors that Influence the Sanitary Condition of Milking Machine Teat-cup Liners

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Abstract
Reports on milking machine sanitation frequently indicate that the physical condition of the rubber parts is important in achieving satisfactory results from a bacteriological standpoint. These references apparently pertain to obvious conditions such as freedom from gross dirt, milkstone, cracking, swelling, and softening of the rubber. More recent reports (1, 2, 3) suggest renewed attention to the rubber as a special harbor of bacteria. Jensen and Bor~ree (7) consider that, under practical conditions, bacteria in teat-cup liners may be lodged in the pores of the rubber. It seems possible that rubber liners, even though in apparently acceptable physical condition, may possess characteristics that are important in sanitation problems. Therefore, consideration should be given to such possibilities in methods used for investigating problems in milking machine sanitation. For determining the bacteriological conditions of milking machines Rnehle et al. (12) devised the "artificial udder" method, which was used subsequently by others (4, 5, 9 ,10). The procedure involves the "milking" of sterile water from the "udder." It presmnably achieves a flexing of the rubber teat-cup liners, simulating the action of the machine under practical operating conditions. Bacterial counts of the water are used to represent the amount of contamination from the machine in an equivalent amount of milk during normal milking. A modification of the procedure has been used recently by Wolvcrton and Cone (13). Rinse and swab methods also have been employed to measure the bacteriological condition of teat-cup liners. Since no vacuum is applied and there is ordinarily no flexing of the rubber, it might be expected that counts obtained by such methods would differ from those obtained by the "milking" technique. In both the "milking" and rinse procedures it has been shown that repeated treatments remove additional numbers of bacteria from the parts examined. In addition to methods for estimating the bacteriological condition of milking machines, it is desirable sometimes to contaminate teat-cup liners and other milking machine parts experimentally in the laboratory. Such procedures permit some control in the amount and uniformity of contamination and facilitate laboratory study of certain sanitation problems before final investigation under practical conditions. The artificial "udder" can be used for this purpose by "milking" through milk of high bacterial content. L~neham (8) has devised an apparatus to "milk" controlled quantities of liquid of known bacterial content through individual liners. His device also can be used for measuring bacteriological conditions of individual liners.