MILK SECRETION 11 



to eat, digest, assimilate, and turn into blood the elements neces- 

 sary to form milk. Some time after parturition there is a 

 tendency toward a shrinkage of the vessels of the udder, and 

 this becomes more marked as the period of gestation advances. 

 All the excess nutrition of the body is needed for the developing 

 fcetus, and hence a lessening of the functional activity of the 

 gland. That pregnancy is an influence tending to diminish 

 milk secretion is demonstrated by the fact that spayed cows 

 will continue to produce milk a long time, even from two to 

 five years, during which time the quantity and quality make a 

 very gradual decrease. While pregnancy Has its influence upon 

 the period of lactation, there are other factors that are of even 

 greater importance and cannot be overlooked, the most im- 

 portant of which is the regularity and thoroughness of the 

 emptying of the gland. If the milking process be done at 

 irregular intervals, or incompletely, the activity of the gland 

 soon ceases. Shortage of feed or water or disease may result 

 in immediate cessation of secretion. The ordinary period of 

 lactation is from nine to ten months throughout the life of the 

 animal. 



" The. nervous system of the cow is closely associated with 

 the production of the milk. When the teats are stimulated, 

 either by the hands or the sucking of the calf, the nerves sur- 

 rounding them become irritated, and through these the nerves 

 of the secreting glands within the udder are excited, causing 

 their contraction and the discharge of their contents. The 

 action of the blood vessels and veins is affected by the activity 

 of the nerves. Ordinarily the greater the capacity of the 

 arteries and veins connected with the udder, the larger the milk 

 secretion will be. This shows the importance of securing cows 

 with a strong development of the arteries and veins of the 

 udder and abdomen. An examination of the belly of a good 

 dairy cow reveals thereon, extending from the udder along each 

 side, a milk vein about one-half inch in diameter. The milk 



