FACILITY OF DIGESTION A FACTOR IN FEEDING als 
/measured by its fuel value (digestible nutrients), is converted 
into heat, and when once it takes this form it is of use only in 
so far as it may be needed to keep the body warm, while it 
cannot be used to replace lost tissues or to build up new. The 
total expenditure of energy in these processes has been desig- 
nated as the work of digestion and assimilation.”* 
Much more energy is required to masticate and digest rough- 
ages than concentrates. The loss resulting from fermentations 
in the digestion tract is also greater with the former class oi 
feeds than with the latter. Zuntz has shown that 11.3 per 
cent. of the energy of hay and 2.8 per cent. of oats was used: 
in chewing these substances. “The same author calculates 
that the work of mastication and digestion combined is 48 per 
cent. of the energy value of the digested material from hay 
and 19.7 per cent. of that from oats.” 
Less digestible nutrients from corn meal, therefore, were re- 
quired for maintenance than from hay, because less energy of 
the feed was used in the work of digestion and assimilation. 
A similar explanation will account for the more rapid gain of 
the pigs fed skim milk than those fed middlings (page 22) ; 
for the more rapid gain of the calves fed skim milk than those 
fed Blatchford’s meal (page 19), and for the greater gain in 
live weight of the cows fed the most concentrates (page 8). 
B. PRODUCTIVE VALUE OF NUTRIENTS IN CONCENTRATES AND 
ROUGH AGE. 
In the preceding experiment it was shown that a consider- 
ably less amount of digestible nutrients was required for main- 
tenance when the ration consisted of corn meal than when com- 
posed of hay. The extra nutrients required in the roughage 
ration is attributed to the extra energy required in digestion 
and assimilation and to the loss of energy resulting from fer- 
*Armsby, Penn. Bulletin 71. 
+Jordan, The Feeding of Animals, p. 165. 
