2i6 Bulletin 397 



In feeding for flesh production an increase in the whole body of the 

 animal is sought, and all feed consumed above that used in maintenance 

 is available for such production. In feeding milch cows, however, the 

 secretion of a single set of glands is the object desired. An increase in 

 body weight in a dairy cow may take place, but it is undesirable, par- 

 ticularly in a feeding experiment. It results in the use of the ingested 

 food for other purposes than milk production, and any considerable fat- 

 tening tends to check the activity of the mammary glands. Thus, 

 improper rations not only may limit the quantity of milk produced, but 

 also may deflect production from milk to flesh. 



Milk secretion is a less understood process than flesh production and 



is much more subject to disturbing factors and to wide variation. In 



this connection Armsby (1917:500) states: 



The feeding of a milking animal is in a certain sense a secondary factor in dairying. 

 The possibilities of successful milk production depend primarily upon the capacity 

 of the animals as milk producers and upon the maintenance of such an environment 

 as will give free play to this capacity. Feed . . . cannot greatly stimulate pro- 

 duction, though it may limit it for lack of material. . . . Improper rations, . . . , 

 even if sufficient in quantity, may if deficient in quality deflect production from milk 

 to fattening, or possibly to greater muscular activity, and thus fail to utilize fully the 

 milk-producing capacity of the animals. 



Milk secretion is a periodic function, having as its object in nature 

 the nourishment of the young. The length of a lactation period varies 

 with different animals, and with the same animal in different years. The 

 decrease in production during a lactation period is also a variable factor. 

 The rate of decrease may vary widely at different stages in the same 

 animal, and may vary from year to year at a corresponding period of 

 lactation. Marked irregularities are frequently shown which cannot be 

 explained by any observed conditions. Toward the end of the lactation 

 period, whether a cow is with calf becomes an important consideration. 

 Gavin (1913 a) has shown that the fall in milk yield due to fetal growth 

 begins from nine to twelve weeks after service. At from seventeen to 

 twenty weeks a decrease of roughly ten per cent was found, and about 

 twenty-five per cent at from twenty-five to twenty-eight weeks. 



Hills (1896) has found variations in yield due to time of calving. He 

 found that a fall cow maintains her production better than does a spring 

 cow, and produces milk of imiform fat content. On the other hand , a spring 

 cow betters the quality of her milk beginning five months after calving, 

 while this was found to be the case with a summer cow at the end of three 

 months. Hills found that abortion caitses a shrinkage of one-third in 

 milk yield, and a gain of one-tenth in quality, as compared with the 

 production of the previous lactation. 



The plane of nutrition is an important factor in feeding experiments, 

 because an increase in weight usually begins before the maximum capacity 



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