MILK SECRETION

Waikato Times, Volume 127, Issue 21280, 26 November 1940, Page 2

MILK SECRETION

N ATURE OF UDDER HOW MILK IS MADE Milk is primarily a secretion—that is to say, a substance built up in a special organ of the body to serve a special purpose, and not merely a means of getting rid of waste material such as urine, which is consequently termed a secretion. But * the udder can also act as an excretory organ, and allows substances to pass through it without change, especially the active principles of certain drugs, and this well-known fact is made use of in medicine as a means of supplying certain drugs in a dilute condition to infants or calves. This, however, is not the normal activity of the udder, but rather its exceptional activity. It is, however, of importance to the dairy industry, for it is probable that most of the taints due to feeding enter the milk in this way, especially where such foods are given shortly before milking. In such cases nature takes the most rapid means of eliminating the waste product, but if the food is given after milking, then the waste product is eliminated from the body by other organs, the true excretory organs, before milking takes place. Cellular Matter The normal function of the udder —the building up of milk—is of a two-fold character; firstly, there is a secretion of a watery liquid or serum, and, secondly, there is a growth of cellular tissue. When the milk is drawn the serum is the first portion to come away, hence the poverty of the first drawn milk. But, as milking proceeds, the cellular tissue begin to break down, and the quality of the secretion improves, so that the last portion to come away is the richest in solid matter, consisting largely of those broken-down sells. It is the skill of manipulating the udder in such a fashion as to bring down this cellular matter which constitutes a good milker, but which is, probably, possessed by the calf to a far greater extent than by any human hands. Natural Fluctuations Natural fluctuations may affect either the quantity of the milk or the quality. The normal conditions of fluctuations are breed, individuality, time since calving—what we may term external influences. Of the normal conditions, the most important are the size and activity of the udder. This depends mainly upon breed. Naturally, small breeds will have large udders, and so the quantity of tlje milk yielded will depend first upon the size of the udder. But the size of the appears to affect mainly off** one portion of the secret! the serum. The of cellular matter lj e broken down does n °l to vary so greatly, we find that while the quantity of the milk varies enormously, the quality does not vary, except in inverse proportion to the quantity. In small cows, the large cellular destruction in the small udder being diluted with only a small secretion of serum produces rich milk. In the large cow a similar amount of cellular destruction produces, naturally, poorer milk. Twofold Nature of Secretion If we wish to understand the mysteries of milk production we must first clearly realise the twofold nature of the secretion, namely, the production of serum and the production of cellular matter, and that the two are more or less independent. For it is mainly owing to the suppression of the secretion of one of these constituents, or to an undue development in the secretion of serum, that nearly all abnormal milk is due. This explains the well-known difference between the morning’s and the evening’s milk where the hours of milking are unequal. The longer the period which has elapsed since last milking the greater the amount of serum secreted, on the one hand, and the more complete the building up of the cells, on the other. This complete building up of the cell contents diminishes the production of fat to the other constituents, and these, so to speak, “ripe” cells being diluted with the increased secretion of serum, the milk fat will frequently fall. On the other hand, in the evening milk of the same cow we have a smaller production of serum coupled with less development of the cell contents, so that the fat is present in greater proportion to the other solids than in the morning’s milk. 1 The longer interval between milking, owing to the resulting dilution with serum, not only diminishes the 'actual amount of solid matter in the milk, but has more effect upon the fat than upon the other constituents. Hence it is that the farmer has to fear in his morning’s milk a deficiency of fat.—F. J. P.