FEEDING HORSES AND MULES 279 



time; but for horses working at ordinary pace only a relatively 

 small protein supply is required. The amounts of non-nitrogenous 

 components of the ration, on the other hand, must be increased 

 with the amount of work done. The standards for work horses, 

 therefore, call for a relatively wide nutritive ratio of 1:6 or 1:7; 

 even this ratio is narrower than that of rations ordinarily fed in 

 this country, unless alfalfa or clover hay is fed, in which case a 

 considerably narrower ratio is fed. Horses in the eastern and 

 northern States are frequently given no other feeds than timothy 

 hay and either oats or corn and oats. The nutritive ratios of these 

 feeds are as follows: Timothy hay, 1:16; corn, 1:9.5, and oats, 

 1 : 5.5. It is evident, therefore, that rations composed of these feeds 

 will be likely to have nutritive ratios of 1:9 or wider. American 

 horses (outside of alfalfa sections) are rarely fed appreciable 

 quantities of high-protein feeds, showing that they require but 

 relatively small amounts of protein in their feed, and that they 

 receive wide nutritive ratios even when at hard work. 



Measurement of Work. The amount of work done by a horse 

 may be measured by one of the usual units of mechanical energy, a 

 foot-pound or a foot-ton. A foot-pound is the amount of energy ex- 

 pended in raising one pound one foot high; a foot-ton is that 

 expended in raising one ton one foot high. The horse-power is 

 another common unit of energy, and is equivalent to 550 foot- 

 pounds per second, or nearly 2,000,000 foot-pounds per hour. A 

 horse's capacity for continuous work is, however, considerably smaller 

 than this amount, and may be put at about 1,000,000 foot-pounds 

 per hour per 1000 pounds weight. Light work done by horses, as 

 commonly understood, will mean from 500,000 to 1,000,000 foot- 

 pounds per hour, medium work from 1,000,000 to 1,500,000, and 

 heavy work from 1,500,000 to 2,000,000 foot-pounds. 1 Instead of 

 measuring the amount of work done by units of mechanical energy, 

 this may be measured in the same way as the potential energy of 

 feeds, by the unit of heat, a Calorie or a therm (p. 45) ; this is a 

 convenient method, because these unit values are now often used in 

 feed analyses and in statements of feeding standards. One Calorie 

 corresponds very closely to 1.54 foot-tons or 3087 foot-pounds. 



The relation of the nutrients required for the production of a 

 certain work by the horse under varying conditions has been studied 

 in extensive investigations by German and French scientists, espe- 

 cially among the former, by Wolff, Zuntz, and Kellner. These 



1 Murray, " Chemistry of Cattle Feeding," p. 153. 



