NUTRITIVE VALUE OF FEEDING STUFFS 41 



Available Energy. — The following computation from an ex- 

 periment with, timothy hay conducted by Armsby will illustrate the 

 method of determining the available energy of a feeding stuff by 

 means of the respiration calorimeter. 



Available Energy of Timothy Hay 

 Energy of feed 



7.50 lbs. timothy hay .■ 13.41 therms 



Energy of excreta 



11.15 lbs. feces 5.47 therms 



. 14.71 lbs. urine 0.61 therm 



0.18 lb. methane 1.10 therms 



Total 7.18 -therms 



Available energy 6.23 therms 



Per 100 pounds 83.07 therms 



A large number of determinations of this kind have been made 

 with feeding stuffs, both abroad and by Armsby and coworkers. 3 It 

 has been found that there is no material difference in the available 

 energy per pound of dry matter in different feeding stuffs of the 

 same kind. There is a marked difference between coarse and con- 

 centrated feeds, however, largely due to the greater losses in the 

 feces of the former feeds. It might be expected from the results 

 stated that the available energy per unit of dry organic matter of 

 different feedsi will be rather uniform, and this has also been found 

 to hold true to a remarkable extent. This fact makes it possible to 

 estimate the amounts of available energy in different feeds from their 

 contents of digestible organic matter by use of certain factors, viz. : 



Roughage 1.588 therms per lb. 



Grains and similar feeds 



with less than 5% digestible fat 1.769 therms per lb. 



with more than 5% digestible fat 1.814 therms per lb. 

 Oil meals, etc 1.996-2.177 therms per lb. 



The figures for available energy do not, however, tell the whole 

 story, because a certain amount of the energy in the feed is largely 

 lost to the animal through the increased body activity in connection 

 with the mastication of the feed, the solution and assimilation of the 

 digested portion, and the passage of the waste through the digestive 

 tract. In an animal at rest the energy thus lost finally takes the 

 form of heat, which can be determined by measuring the additional 

 heat production caused by the feed consumed. An example will show 

 how the energy expended in feed consumption is calculated: A 

 steer consuming 7.5 pounds of timothy hay per day produced 7.79 

 therms of heat; in the following period the hay ration was in- 

 creased to 12.34 pounds and the heat production rose to 9.52 therms. 

 It follows, therefore, that each additional pound of hay increased 

 the heat production by .3575 therm ; that is, this amount of energy 



■ Jr. Agr. Res., 3, p. 435; Penn. Bui. 142, p. 10. 



