MASSACHUSETTwS ANIMAL INDUSTRY -^^^ 



THE UTILIZATION OP FEEDS BY HORSES 

 By J. B. LINDSEY AND J. G. ARCHIBALD 



Although it is recognized that for many industrial purposes the autonioljile, 

 auto truck and farm tractor have rephiced tlie horse as a source of power, we 

 believe that the horse, for a long time to come, will continue to have his place 

 upon the farm and in certain other lines of industry. 



For a number of years studies have been made at this Station of the 

 digestibility, metabolizable energy and net energy of the ordinary roughages, 

 grains and by-products likely to be fed to farm and other work horses in 

 order to ascertain their relative nutritive values. 



Units of Measurement. 



In order to get at relative nutritive values, we must have one or more 

 units of measurement. Obviously the foot rule or the yardstick would not 

 serve for such a purpose. The best units we have are (a) chemical analysis 

 of the feed, (b) its digestibility, (c) its total, metabolizable and net energy 

 values. 



(a) Chemical analysis tells how much of each of the several groups, pro- 

 tein, fat, carbohydrate and ash, a feed contains but it does not tell how much 

 of each group the animal can finally utilize. 



(b) Digestibility. By digestibility is meant the amount of each ingredi- 

 ent the animal can digest or so transform that it can be carried into the 

 blood stream and made use of as food. The solid excreta or feces is the 

 undigested portion of the feed which, subtracted from the total feed, leaves 

 that which is digested. The digestion coefficient means simply the percentage 

 of the feed or ingredient digested. Thus, if a feed contains 30 per cent or 

 pounds of fiber in 100 pounds and 1.5 pounds is digested, the coefficient is 50. 



(c) Energy. Every food may be regarded as a mass of latent energy. 

 Digestion liberates this energy and the animal lives and produces, as a result 

 of the liberation. 



Total energy represents all of the energy contained in a feeding-stuff, and 

 is determined by the use of a complicated piece of apparatus known as a 

 bomb calorimeter 



Metabolizable energy is the total energy less that contained in the feces and 

 urine. 



Net energy is the total energy minus that lost in the feces and urine and 

 that used in the process of digestion and assimilation. 



While the determination of digestibility tells us the amount of a food di- 

 gested, it does not tell the cost to the animal of the energy expended in the 

 digestive processes. Comparative digestibility of feedstuffs, however, is a very 

 helpful unit of measurement, but net energy is the more exact. Unfortunately 

 the present method for determining net energy is very difficult, expensive and 

 time consuming. The only equipment available in the United States for large 

 animals is that at the Institute of Animal Nutrition in Pennsylvania, financed 

 by the National Government. The late Professor Armsby, the director of 



