468 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



periment is begun. The composition and quantity of the milk is 

 then determined for a period of ten days. A test period follows in 

 which the feeds to be tested are compared. One method of pro- 

 cedure is as follows : Suppose Indian corn and Kaffir corn are 

 to be compared. All groups are fed roughage, concentrates, and 

 equal quantities of Indian corn and Kaffir corn during the pre- 

 liminary period. At the beginning of the test period, Group A 

 receives Kaffir corn in place of Indian corn and Group B Indian 

 corn in place of Kaffir corn. Group C receives the same ration 

 as before, containing equal parts Kaffir corn and Indian corn. 

 Including the transition period, the feeding test lasts I to 2 

 months, and every 8 to 10 days, as before, the average milk pro- 

 duction is determined. In the last 10 days of the period the 

 composition of the milk is also determined. An after period of 

 i to 2 months follows, in which the food is the same as in the 

 preliminary feeding period. The live weight is also to be de- 

 termined on three successive days at the end of each period and 

 in each sub-period. All factors except the feed tested should 

 remain constant. 



Effect of Nutrition on Milk Production. The composition and 

 quantity of milk depends ; first, upon the capability of the animal 

 and the state of lactation ; and secondly, upon the food. The 

 animal cannot increase the milk flow above the limits of the 

 capacity of the animal. An excess of feed will go into body fat. 

 A deficiency of food will decrease the milk flow, shorten the 

 period of lactation, and may permanently injure the productive- 

 ness of the animal. The food should be adjusted to the greatest 

 quantity of milk possible to be produced and should be decreased 

 gradually during the period of lactation. When the ration is 

 reduced from a sufficient to an insufficient one, the milk glands 

 do not respond immediately to the change, but they consume more 

 or less body substance for the production of milk, and the condi- 

 tion of the animal becomes visibly worse. This fact is observed 

 so often with cows fresh in milk, that many believe that cows 

 must always become thinner after calving. But the effect of in- 

 sufficient food soon shows in a decrease in the quantity of milk 



