236 A Manual of Veterinary Physiology. 



various ratios, we obtain an insight into the chemical 

 arrangement of its constituents, and as the proportion 

 which these bear to each other considerably influences the 

 digestion of a food, the matter is one of practical import- 

 ance. 



The desirable nitrogenous ratio of a diet depends upon the 

 class of animal, the age, and, in the case of the horse, the 

 work which is expected. In the young and growing animal 

 the proportion of proteids to the carbo-hydrates, minus the 

 indigestible fibre, should be 1 : 2 ; at middle age it should 

 be 1:3; in the adult, 1 : 5. The calculation is effected by 

 dividing the nitrogenous material into the sum of the 

 starch, sugar, and digestible fibre. 



The fatty ratio of a food is obtained by dividing the fat 

 into the quantity representing the nitrogenous portion ; the 

 most favourable fatty ratio should not be more than 1 : 2*2 

 or less than 1 : 3. 



The complete nutritive ratio of a food is obtained by 

 dividing the nitrogenous quantity into the whole of the 

 non-nitrogenous ; the chief object of this ratio is to show 

 the proportion of indigestible fibre existing in a food. The 

 complete nutritive ratio should be about 1 : 87 or 1:9; if 

 it be 1 : 10, 1 : 12, or 1 : 15, it would indicate an undue pro- 

 portion of cellulose and lignin, and such a diet would be un- 

 fit for hard-working horses, though suitable for cattle. For 

 horses performing ordinary work, a ratio of from 1:8 to 

 1 : 8 - 5 is suitable; for hard-worked horses, particularly for 

 fast work, 1 : G or 1 : 7 is judicious. 



In the determination of all these ratios, the salts of the 

 food are not taken into consideration. 



It is important to remember that the nutritive value of 

 a food is not, absolutely determined by its chemical analysis ; 

 bran, for example, gives an excellent analysis, but its 

 nitrogen is useless for feeding purposes. 



