MILK SECRETION

New Zealand Herald, Volume LXXVI, Issue 23470, 6 October 1939, Page 12

MILK SECRETION

SCIENTIFIC PROBLEM SOME WASTEFUL METHODS ROLE OF UDDER PRESSURE HY OUIIMRIt The mystery of tlin secretion of milk from the blood stream still Imfi'les investigators, but in tlio course of research into this subject much of practical value to the dairyman has been learned. For instance, it has been proved that except during a short period immediately following milking milk secretion is a steady and continuous process. This explodes the popular idea that a great part of the milk is secreted during the actual process of milking. Secretion is most rapid in the re-cently-emptied udder, but gradually' decreases in rate as the pressure of milk within the udder increases. As the pressure increases and secretion is slowed up re-absorption into the blood stream of some of the milk takes place and the fats arc the first to be absorbed. If, by repeated frequent milkings, the udder is never allowed to become tightly distended, the percentage of butter-fat is constant, and the milk production is increased. 'I ho reason why morning's milk is frequently lower in butter-fat than the night's yield is thus explained by the longer period between evening and morning milking which is the rule on most dairy farms.

It has been proved that more milk is produced per hour when the pressure is low than when it is allowed to become high. This indicates that the ideal udder on n dairy cow should be soft and elastic, and of great capacity, capable of expanding easily as the milk is secreted without any appreciable increase in pressure. Even with cows having such udders, and with a high yield, it would be economical during the flush of the season to milk them three times a day instead of twice, and at regular intervals of time —as every eight hours —to keep the pressure low. It is also important that, at any time, tlio herd should be milked at regular intervals of 12 hours instead of one of 16 ftnd one of eight hours, as is now often the practice. When actual milking commences there is found to be a considerable increase in udder tension or pressure resulting from nerve stimulation of the teat which leads to a nerve muscle reflex which tenses the tine network of muscle fibres present in the udder. This forces the milk out of the secreting ducts and tissue into the milk cisterns. This effect is noticeable as the cow "letting down her milk." It is possible for the cow in a nervous state, or in strange surroundings, to control and prevent this reflex, in which case she "holds up her milk." Also, this tensing of the udder onlv continues for a limited time, which varies with individual cows. The muscle fibres becomo tired, and so relax, and the milk is retained in the fine ducts of the secreting tissue. This explains the greater quantity of milk got from cows by fast milkers, and also the greater necessity, in the case of slow milkers or slow milking machines, of stripping. More and richer milk is obtained by a quick, strong milker than by a "slow, inefficient milker, and with milking machines a greater quantity of rich milk will be won and less stripping will be necessary ? when the four quarters are emptied in as short a time as possible.