Shkehy — The Influence of Feeding on Milk Fat. 479 



fed cows the subsequent feeding of an abundant ration resulted in an 

 inci'ease in the percentage of fat as well as an increase in the total milk and 

 total fat. The experiment continued over a number of years. Yet Eiihle 

 [1919] and Pritzker [1919] find, from a large number of analyses made 

 during the period 1914-18, no evidence to show that food deficiency causes 

 a decrease in the fat content of milk. Data collected by the Dairy Section 

 of the Department of Agriculture and Technical Instruction for Ireland 

 does not lend support to this view, but is rather in agreement with the 

 work of Wing and Foord. Eeferring to the effect of water in the food on 

 the composition of milk, Turner, Shaw, Norton, and Wright [1916] state 

 that the water content of a ration has no effect on the composition of milk 

 yielded therefrom ; and Berry [1921] comes to the same conclusion. It is 

 evident that there is no unanimity of opinion among previous investigators 

 as to the effect of feeding on milk fat. 



Much of the work referred to was done on good condition cattle, con- 

 tinuously getting abundant supplies of food, so that the effect of the changes 

 in diet was difficult to detect. Besides, changes were made by completely 

 substituting one food for another, so that usually more than one food con- 

 stituent was involved. For instance, the subsfitution of brewers' grains for 

 cotton cake involves a change in the quantity of carbohydrates and fats, and 

 in the quantity and quality of the proteins. Thus more than one variable 

 was introduced, and there was not a clear comparison of the effect of one 

 food ingredient with that of another. Eealizing the necessity for conducting 

 such an investigation under conditions approximating to laboratory control, it 

 was decided in this investigation to substitute goats for cows. To the diet of 

 these animals the individual food constituents could be added at comparatively 

 small cost, while at the same time sufficient milk is yielded to afford a consider- 

 able margin for fluctuation resulting from experimental changes in conditions. 

 In the goat, as in the cow, the milk yield is highest at the beginning of 

 lactation, and it declines gradually towards the end. The lactation period, 

 in the case of the old Irish breed, usually begins in April and terminates 

 about December. As in the cow also the percentage of fat in the milk 

 tends to increase as lactation advances, and the weight of the animal's body 

 similarly increases towards the termination of the milk flow, especially with 

 liberal feeding. The general procedure in this investigation was first to 

 observe the quantity of food which just maintained the animal's weight and 

 at the same time yielded a constant flow of milk, and then test the effect of 

 adding to this " milk and body maintenance " ration different quantities of 

 individual food constituents. Then, when the effect of an addition to the 

 ration was determined, the effect of the withdrawal of that addition was 

 subsequently investigated. Extra food assimilated above the "milk and 



