60 FEEDS AND FEEDING 



This is probably the chief reason why a quiet steer which will ' ' eat and 

 lie down' 7 makes more economical gains than a wild or nervous animal. 

 This effect of difference in temperament also explains why some horses 

 are much "easier keepers" than others. It has been found that the 

 presence of flies caused a horse to burn 10 per ct. more fuel in its body 

 than normally, a fact which has a practical bearing in feeding stock. 3 



Armsby 4 found that steers when standing required 41 per ct. more 

 nutrients for maintenance than when lying down. This is partly due to 

 the work of maintaining the body upright and also to the greater mus- 

 cular movement of the animal when standing. The condition of an 

 animal influences the maintenance requirement somewhat, a fat animal 

 requiring more feed for maintenance than a lean one of the same weight 

 or of the same body surface. 5 



It has been shown on the preceding page that the chief loss of heat 

 from the body is by radiation. Such loss of heat from solid masses has 

 been found by scientists to be proportional not to their weights, but to 

 their surfaces. This is because large bodies have less surface per pound 

 than small ones. Theoretically, therefore, maintenance rations for ani- 

 mals of various sizes should be computed on the basis of the body surface 

 and not live weight. Since it is difficult to measure the surface of an 

 animal's body, the body surface may be computed by the well-known 

 geometrical law that the surfaces of solids are proportional to the 

 squares of the cube roots of their weights. In scientific trials, main- 

 tenance rations have usually been computed on this basis.* However, 

 Armsby found in his trials that the actual maintenance requirements 

 of steers of various weights and ages correspond as well with their live 

 weights as with their body surfaces, as computed by this formula. In 

 the Morrison feeding standards the maintenance requirements are stated 

 per 1,000 Ibs. live weight, assuming that this will give results of sufficient 

 accuracy in figuring rations under practical conditions. 



The rate at which heat is lost from the body by radiation also depends 

 on the difference between the air temperature and the body temperature. 

 Due to this Trowbridge, Moulton, and Haigh found at the Missouri 

 Station 6 that the maintenance requirements of an animal are less in 

 the spring than in the winter. In the summer they are higher than in 

 spring, due to the extreme heat and the presence of flies. They also 

 found that unthrifty animals required much more feed for maintenance 

 than healthy ones. The maintenance requirement of young animals was 

 greater than of older ones of the same weight. 



Exposure to cold winds, especially with animals having scant coats, 



8 Landw. Jahrb., 23, 1894, p. 161. 



Mour. Agr. Research, 13, 1918, pp. 43-57. 



5 Armsby, Jour. Agr. Research, 11, 1917, pp. 451-72. 6 Mo. Research Bui. 18. 



*Moulton states (Mo. Res. Bui. 30) that the maintenance requirements of 

 fat steers are more nearly proportional to the five-ninths power of their weights, 

 and of steers in medium to thin condition to the five-eighths power of their 

 weights. 



