MEASURING THE USEFULNESS OF FEEDS 



35 



Subtracting the amounts of dry matter and of the difiPerent nutrients 

 in the feces from the amounts in the feed, we find the amounts digested. 

 From this we compute the percentage of each which is digested. For 

 example, there was 17.4 lbs. of dry matter in the 20 lbs. of hay the cow 

 ate each day. Of this, 7.1 lbs. was excreted in the feces, leaving 10.3 

 lbs., or 59.2 per ct., as the part digested. 



Some feeds cannot be fed alone, as was done in this trial. For 

 instance, horses and ruminants are not fed concentrates alone without 

 hay or other roughage. Again, while pigs may be fed on grain only, 



Fig. 12. — A Steer in a Digestion Stall 



In digestion trials tlie feces may be collected in seA'eral ways. A common man- 

 ner is by means of the liarness and rubber duct here shown. When it is merely 

 desired to determine the digestibility of a feed, the urine need not be collected. 

 In other nutrition studies the urine must be collected, as is being done in this 

 trial. (From Armsby, Penn. Sta.) 



such feeds as tankage and linseed meal are too rich in protein to be 

 so fed. The digestibility of such feeds must, therefore, be found by 

 difference, instead of directly. To illustrate, a horse is first fed hay 

 for several days and the digestibility of the hay determined. Oats 

 may then be added to the ration, and the total amounts of nutrients 

 digested from both feeds are found, just as in the preceding method. 

 The amount of digestible nutrients coming from the hay is then sub- 

 tracted from the total, leaving the amount assumed to be digested from 

 the oats. 



