28 THE ECONOMICS OF FEEDING HORSES 



other food of known composition and digestibility, and 

 the proper deductions made in estimating the excreta. 

 An even more exact determination of the digestibility of 

 a food can be made by means of an apparatus known 

 as a "respiration chamber," in which the animal is 

 placed during the course of the feeding experiment, so 

 that not only the urine and faeces can be obtained for 

 analysis, but the intake of oxygen and output of carbon 

 dioxide by the lungs can also be determined. By this 

 means a complete record of the animal's intake of food 

 and excretion of undigested and waste products is 

 obtained ; and, further, the method is of great value 

 in determining the use of food in relation to work. For 

 the purposes of this book the results of the digestion 

 experiments carried out by Wolff, Kellner, Zuntz, and 

 other German workers, have been entensively used, 

 though some figures are taken from Jordan and Hall's 

 compilation published by the United States Bureau of 

 Animal Industry. Out of 100 parts of a food supplied, 

 the number of parts digested is stated, and this number 

 is called the digestion coefficient of that particular food. 

 Of course, these figures refer to the digestion of a good 

 sample of the food by a horse in normal health and 

 under normal conditions. 



There are circumstances which altogether alter the 

 digestibility of a food, and some of these must be men- 

 tioned now. The quality of the food itself is undoubtedly 

 a factor, for just as quality affects the chemical composi- 

 tion, so it affects the digestibility. Bad as a poor sample 

 of food may be shown to be by analysis, it may be, in fact, 

 much worse in the animal because of lowered digesti- 

 bility. Especially in the horse does excess of crude 

 fibre lower the digestion coefficients. Again, a food 



