174 PRINCIPLES OF POULTRY FEEDING 
Some of the feed eaten is not digested and is voided with the 
droppings. Only that part which is capable of digestion is of 
value in nutrition and worthy of consideration by the feeder. The 
undigested residue must be subtracted from the original material 
in computing nutritive value. It is only the digestible nutrients 
which are available for assimilation. This fact is important and 
should be borne in mind in selecting feeds, as many which are rich 
in certain nutrients have a very low digestibility. The percentage 
of a feed which is digestible is called the “‘ digestion coefficient.” 
For example, whole wheat grains contain 11.9 per cent of protein, 
only 80 per cent of which is digestible or of assimilative value; hence, 
out of every 100 pounds fed, containing 11.9 pounds of protein, only 
9.5 pounds are of use to the fowl. Digestion bears a direct ratio to 
the health of the flock; and the stronger and healthier the birds are 
the better able they will be to digest a large amount of feed and get 
all of the possible good out of it. The following are some of the 
factors which affect the value or the digestibility of feeds: 
(1) Young, tender shoots of grasses and forage plants are more 
digestible than mature tissues; hence, they have a higher value 
than if allowed to become old and woody. 
(2) Grains or by-products if exposed to rains or dampness 
during the process of curing or storing will have a greatly reduced 
value as compared to those cured under favorable conditions. 
(3) A ration not properly balanced will tend to waste the 
surplus nutrients. (See Chapter XII.) 
(4) The digestibility of feed for poultry is seldom increased 
and often found*to be decreased by cooking. 
(5) The indigestible portion of feeds may serve in some in- 
stances to give needed bulk to a ration, but it often places a heavy 
tax on the energy of the fowl and sometimes offsets entirely the 
nutritive value. 
Aside from the digestibility of feed, the question of its physical 
effect on the condition of the individual is an important considera- 
tion. The point to determine is whether the ration is best suited 
to the birds to which it is fed. Feeds which in themselves are 
valuable may cause disastrous results if improperly fed or if given 
to a wrong type of birds; for example, ground green bone is highly 
nutritious, but if fed in excess will often upset the digestive system 
and thus retard the object sought,—namely, that of increasing egg 
production. Hence, ease of digestion is as important a factor as 
total digestibility. Milk is both entirely digestible and easily 
