TYPES AND MARKET CLASSES OF LIVE STOCK 163 



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 capac- 

 ity. In young heifers that have never had a calf, the udder con- 

 tains 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 incomplete 

 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 advantage 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. Regularity in milking is essential 

 to best results, both in the amount secreted per day and in the 

 length of the lactation period. 



