44 FEEDS AND FEEDING 



stored; i. e., whether it formed part of proteins built into body tissues, or whether 

 it was stored as fat. 



From the nitrogen analyses of the feed it was found that the total intake of 

 nitrogen in the feed consumed by the steer was 0.683 Ib. A loss of 0.231 Ib. 

 nitrogen occurred in the undigested matter of the feces and a further loss of 

 0.375 Ib. in waste nitrogenous material in the urine, making a total loss of 

 0.606 Ib. Subtracting this from the total intake of nitrogen, 0.683 Ib., it was 

 found that the steer gained 0.077 Ib. of nitrogen during the day. This must have 

 been built into the protein tissues of the body. 



From the data secured it is possible to compute in the following manner the 

 actual amount of protein and fat stored in the body of the steer during the day. 

 To find the amount of protein stored we multiply the 0.077 Ib. of nitrogen stored 

 by 6.25, which gives us 0.48 Ib. of dry protein tissue stored in the body. As 

 carbon forms, on the average, 52.5 per ct. of protein body tissues, about 0.25 Ib. 

 of the carbon stored in the body must have been built into this protein. 



Subtracting this amount of carbon from the total stored, 0.73 Ib., we find that 

 the difference, 0.48 Ib., must have been stored as fat, for the carbohydrate 

 (glucose and glycogen) content of the body of an animal at rest does not vary 

 from day to day. This 0.48 Ib. of carbon formed about 0.63 Ib. of fat, for pure 

 animal fat is on the average, 76.5 per ct. carbon. 



As fresh lean meat or other protein body tissue is nearly two-thirds water, 

 the 0.48 Ib. of dry protein stored in the body equaled about 1.25 Ibs. of fresh lean 

 meat or other protein tissues. The body fat of a steer is about two-thirds fat and 

 one-third water; hence this steer gained about 1.00 Ib. of fatty tissue during the 

 day. This careful respiration study therefore shows that from the feed consumed 

 by the steer during 24 hours he stored in his body about 1.25 Ibs. of fresh protein 

 tissue and 1.00 Ib. of fatty tissue. 



By analyzing feeds, feces, and urine for mineral matter, it is possible to 

 determine in the same manner as in the case of nitrogen, just how much total 

 mineral matter the animal has gained or lost in a day, or how much of any 

 particular mineral constituent, as calcium or phosphorus. 



75. The respiration calorimeter. A still more accurate means of meas- 

 uring the usefulness of feeds is furnished by the respiration calorimeter. 

 This is an improved and exceedingly complicated form of the respi- 

 ration apparatus, in which not only the feces, urine and gaseous waste 

 products can be analyzed, but in which the heat given off by the animal 

 can also be accurately measured. By means of this apparatus, it is 

 possible to find exactly how much of the gross energy of the feed the 

 animal has been able to use in growth, fattening, work, or milk pro- 

 duction. The first and only respiration calorimeter built in this country 

 for carrying on experiments with large animals was erected by Armsby 

 at the Pennsylvania Station some years ago thru the co-operation of 

 the United States Department of Agriculture. 5 



76. Gross energy of feeds. A mature animal may be compared to a 

 steam engine, in which a part of the power derived from the fuel is 

 used for the operation of the engine itself, while the surplus may 

 perform useful work. The steam engine derives its energy from coal 

 or wood; the animal from the feed it consumes. Both require a small 

 amount of repair material steel, brass, etc., for the engine, and protein 

 and mineral matter for the animal but the largest demand with engine 

 and mature animal alike is for fuel. It is therefore both important and 

 interesting to consider the relative value of feeds in terms of the fuel 

 they can furnish the body. 



Expt. Sta. Eecord, 15, pp. 1037-50; U. S. D. A., Bur. Anim. Indus. Bui. 51. 



