Types and Market Classes of Live Stock 187 



Colostrum. — Because of more or less incompleteness of the various 

 processes of secretion at the start of the lactation period, the first milk 

 differs in composition from that afterwards secreted, and is called 

 colostrum. It is thick and viscous, contains less water than normal 

 milk, five times as much albumin, twice as much ash, slightly more fat, 

 and about one-half the usual percentage of sugar. It has a laxative 

 effect on the calf, useful in properly starting the work of digestion. 

 In about one week following birth, the yield of milk usually increases 

 and becomes normal in composition. 



Stimuli to secretion. — The cow has no control over the secretion 

 of milk, it being involuntary. During the latter part of pregnancy, 

 the embryo calf makes very rapid growth, and the blood supply to the 

 placenta is much increased. At that time the cow does not ordinarily 

 secrete milk, her excess of energy being given to the growth of the 

 embryo. When the calf is born, the demand through the placenta 

 ceases, and the large volume of blood is turned toward the udder. A 

 short time previous to calving, the udder of the cow shows considerable 

 increase in size, and by the time the calf is born the mammary glands 

 are fulfilling their function nearly to the maximum capacity. In 

 young heifers that have never had a calf, the udder contains a watery, 

 saline fluid. Regular attempts at milking, or manipulation of the 

 udder with the hands, or allowing a calf to suck, may stimulate the 

 secretion of considerable normal milk in such young heifers. The 

 same methods have been known to cause the secretion of a milk-like 

 fluid by the rudimentary glands of males. Thorough milking furnishes 

 a stimulus that causes prolongation of the lactation period, while incom- 

 plete removal of milk tends to check the secretion and shorten the 

 milking period, and it may also cause serious inflammation. Frequent 

 milkings tend to increase the flow of milk, but there is no special ad- 

 vantage in milking more often than twice a day unless the cow is a 

 high producer and the udder becomes very much distended between 

 milkings, as such distention acts as a check to further secretion. Reg- 

 ularity in milking is essential to best results, both in the amount 

 secreted per day and in the length of the lactation period. 



