SECRETION OF MILK 403 
In choosing cows with large milk capacity look sharply to the 
extent of the development of the milk veins. These are the chan- 
nels by which the red blood is connected with the organs of milk 
secretion. Large milk veins, therefore, are indicative of a large 
milk yield. 
6. Factors influencing secretion.—The three most im- 
portant things to look for in a good dairy cow are indica- 
tions of robust health, a large digestive capacity .and 
proper mammary development. The amount of the 
blood,and its richness, which passes through the udder has 
much to do with milk secre- 
tion. The udder is naturally 
of first importance. It is not 
the size or shape or appear- 
ance that matters most, but 
the internal structure; and 
this touches on the inherit- 
ance, breeding and training 
of the cow. Hence, the cell 
structure and number and 
size of blood vessels of the 
udder influence in greatest 
measure the yield of milk. 
7. Why milk is secreted. 
—During fetal life an off- 
spring is nourished by its 
mother’s blood. At birth 
this consumption of blood 
food is cut off entirely. 
The course of the blood is 
changed and directed into 
the udders. This is a sim- 
ple turn from the arteries 
of fetal nourishment to the Note the fine development of the 
fF H 1 milk veins along the abdomen and on 
arteries of imiulle secretion, 7 rome 
MILK VEINS 
