Outlines of dairy bacteriology, 10th edition / A concise manual for the use of students in dairying

by H. L. Russell; E. G. Hastings

The infection traceable directly to the cow is modified materially by the conditions under which the animal is kept and the character of the feed consumed. The nature of the fecal matter is in part dependent upon the character of the food. The more nitrogenous the ration fed, the softer are the fecal discharges, producing a condition which is more likely to soil the coat of the animal unless care is taken. The same is true with animals kept on pasture in comparison with those fed dry fodder.

Stall-fed animals, however, are more likely to have their flanks fouled, unless special attention is paid to the removal of the manure. All dairy stalls should be provided with a manure drop which should be cleaned as frequently as circumstances will permit.

Fig. 9.—Bacteria on Hairs.
Each colony on the hair represents one or more bacteria that were adherent to the hair when it was placed on the surface of the solid culture-medium.

The animal contributes materially to the quota of germ life finding its way into the milk through the dislodgment of dust and filth particles adhering to its hairy coat. The nature of this coat is such as to favor the retention of these particles. Unless care is taken, the flanks and udder become polluted with fecal matter, which upon drying is displaced with every movement of the animal. Every hair or dirt particle so dislodged and finding its way into the milk-pail adds its quota of organisms to the liquid. This can be readily demonstrated by placing cow's hairs on the moist surface of gelatin culture plates. Almost invariably bacteria will be found in considerable numbers adhering to such hairs, as is indicated in Fig. 9.

Dirt particles are even richer in germ life. Not only is there the dislodgment of hairs, epithelial scales, and masses of dirt and filth, but during the milking process, as at all other times, every motion of the animal is accompanied by a shower of invisible particles, more or less teeming with bacterial life. All of this material contains organisms that are more or less undesirable in milk. Bacteria concerned in gassy fermentations and those capable of producing obnoxious taints are particularly common, so that this type of pollution is especially undesirable in milk.

Amount of dirt in milk. When one remembers that the larger part of fresh manure is of such a nature that it does not appear as sediment, the presence of evident filth in milk must bespeak careless methods of handling.

The sediment or dirt test is used quite extensively to ascertain the amount of dirt milk may contain. By means of a cotton filter, the insoluble residue is removed and is made evident upon a layer of absorbent cotton. Milk that would show with difficulty any evidence of dirt upon ordinary examination reveals such defects very readily in this test.

Exclusion of dirt. It is better to keep bacteria out of milk, so far as practicable, rather than to attempt to remove them after they have once gained entrance. As is usual, prevention of trouble is much more easily accomplished than removing the difficulty after it once occurs.