RELATIVE VALUES OF FEEDING STUFFS 593 



full vigor. A very considerable share of the investigations in 

 stock feeding during the last two decades, especially perhaps in 

 the United States, has consisted of experiments intended to 

 determine the effects of the substitution of one feed for another 

 in a ration. 



Undoubtedly the so-called practical trial has an important 

 part to play in the development of a sound theory of feeding as 

 well as in relation to the economic aspects of the subject. Re- 

 garded, however, simply as a means for the quantitative deter- 

 mination of the relative values of feeding stuffs it is subject to 

 precisely the same limitations and uncertainties as the old at- 

 tempt to determine hay values, and in this respect has in 

 general led to scarcely more satisfactory or concordant results. 

 It is as true in the later as in the earlier experiments that 

 the effect of a feeding stuff may vary widely with the com- 

 bination in which it is fed and the conditions under which 

 it is used. 



702. Feed units. An interesting attempt to revive the 

 fundamental conception of hay values in a modified form and 

 within a restricted field, and thus to retain the advantage of 

 expressing the relative value of a feed by a single number, 

 is found in the so-called feed unit system devised by Fjord 

 and his associates in Denmark and extensively used also in 

 Sweden. 1 



The feed unit system, like that of hay values, is essentially a 

 system of empirical equivalents according to which feeding 

 stuffs may replace each other. Instead of hay, the basis of 

 comparison is a unit weight of grain (corn, barley, wheat or 

 rye or a mixture of grains). This is called a feed unit and the 

 amounts of other feeds required to equal the feed unit have 

 been determined in very extensive cooperative feeding experi- 

 ments by the group system (572) with swine and especially with 

 dairy cows. The experiments themselves have been executed 

 with every precaution to ensure accuracy. The results for 

 dairy cows, as revised by Woll for American feeding stuffs, 

 and the Danish values for swine and for the horse are given by 

 Henry and Morrison 2 as follows : 



1 For a more complete discussion of the feed unit system compare Woll ; Wis- 

 consin Expt. Sta., Circular No. 37. 



2 Feeds and Feeding, isth Edition, p. 127. 



2Q 



