204 THE CREAMERY PATRON'S HANDBOOK. 



salts in milk do not exist in the same relative proportion as in the blood 

 which also tends to disprove the theory so long maintained that the separa- 

 tion of milk is largely a process of transudation. 



QUANTITY AND QUALITY OF MILK SECRETED. 



Wild animals secrete only a sufficient quantity of milk to meet the 

 needs of their young until they become sufficiently developed to secure 

 their own food. Under the influence of domestication the functional ac- 

 tivity of the gland has been greatly developed both in the quantity produced 

 and in the duration of the period of lactation. In all good dairy cows 

 the period should extend over several months, and in some it is practically 

 continuous. The average yield per cow is less than 4,000 pounds per 

 annum, but in good dairies it is more nearly 6,000 pounds, and in individuals 

 it will greatly exceed that amount. In one instance it was over 30,000 

 pounds. 



The flow of milk is greatest shortly after parturition and gradually 

 decreases until the close of lactation. 



As milk is dependent upon the metabolism of the mammary gland, 

 this is in turn dependent upon the quantity of blood passing through it. 

 For large milking capacity it is necessary that there should be large gland- 

 ular development, but more important still, a large circulation of blood 

 in the part. The cow must receive an ample supply of food and have the 

 capacity to eat, digest, assimilate and turn into blood the elements necessary 

 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 foetus, 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 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 important 

 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 first and second periods are somewhat shorter. 



The quantity and quality of milk secreted each day is fairly constant. 

 Variations do occur within certain limits and may be due to numerous 

 causes. In general, the evening milk contains about a half per cent, more 

 fat than morning milk, but the latter exceeds the former by about 25 per 



