Refinement of Feeding Experiments for Milk Production 219 



As a result of six years trial Hills (1907) advances the opinion that this 

 scheme is inferior to the simple alternation system, particularly if only 

 a small number of animals are available. 



Relative merits of the three systems 



The advantage of the alternation system lies in the fact that the trial 



of the two sets of rations with the same animals eliminates many of the 



factors due to individuality and obviates uncertainties in attempts to 



make up groups of like production. On the other hand, the use of the 



alternation system necessitates a short feeding period. Hills (1907) 



recognizes this disadvantage. In this connection he quotes Babcock as 



follows (page 1 1 7 of reference cited) ; 



It seems likely . . . that there are certain reserve forces which enable an animal 

 to adapt itself to adverse conditions and even to overcome the effect of malnutrition 

 for much longer periods than have heretofore been considered sufficient. 

 Much additional knowledge concerning the physioiogical influence of foods may be 

 gained, and thereby many of the uncertainties which exist to-day regarding feeding 

 problems be eliminated, by greatly extending the experimental periods. 



Thome, Hickman, and Falkenbach (1893:82), after two years use 

 of the alternation system, say:' "We need to expand the 90-day test 

 into a 1 2 -month test . . . We might as well drop the three or four- 

 week test altogether." 



Another disadvantage of the alternation system results from the residual 

 effect of a given ration on a succeeding one. Armsby states (1917: 525): 

 "It is not an unusual experience in dairy feeding experiments to see a 

 change of rations followed by a temporary stimulation of the milk pro- 

 duction which is not sustained." 



Woll (1904) states that any change in the system of feeding is generally 

 accompanied by an immediate disturbance of the normal character of 

 the production of the cows, and that several weeks may be required for 

 adjustment. Those who have used the alternation system have endeavored 

 to offset this residual effect by the use of a preliminary period. However, 

 these periods have imquestionably been too short in most cases. Indeed 

 there is a question whether, when a ration has been used which reduces 

 a cow's production considerably below normal, the cow can be brought 

 back to normal production during the given lactation period. Soule 

 and Fain (1905), speaking of their use of the continuous system, state 

 that, tho they recognize its defects, they consider it preferable to the 

 alternation system because of the time required to get a cow under the 

 influence of a given foodstuff. 



The continuous system obviates the disadvantages of the short feeding 

 period and the residual effect. On the other hand, in this system ques- 

 tions arise as to the equaHty of individuals and groups selected on the 



329 



