RATIONAL FEEDING OF ANIMALS 345 



been fed. Growth, work and animal products are all 

 produced from the excess of nutrients over those required 

 for maintenance purposes. For example, a pig weighing 

 200 pounds requires about five pounds of grain per day 

 for maintenance. If 5.5 pounds per day are fed, an in- 

 crease in weight is secured only from the half pound in 

 excess of the maintenance ration. 



469. Standard Rations. For feeding purposes stand- 

 ard rations have been proposed, giving the amounts of 

 nutrients required by different classes of animals for dif- 

 ferent purposes. These tables have been prepared largely 

 as the result of digestion experiments and feeding trials. 

 The table in most common use is that prepared by Woulff 

 and modified from time to time by various investigators. 

 This table is given at the close of the chapter. 



470. Food Requirements of Animals. In the feeding 

 of balanced rations, tables of feeding standards should be 

 used largely as guides. It is not necessary that the 

 rations should, in all particulars, absolutely conform to 

 the standards given. On the other hand, it is not advi- 

 sable to have the amounts of nutrients in the rations vary 

 in any large degree from the standards. It is difficult to 

 specify the amounts of nutrients which, under all con- 

 ditions, will meet the food requirements of all classes of 

 animals. In previous chapters, it has been shown that 

 the composition of forage crops is subject to variation as 

 is also their digestibility. Hence, tables giving the 

 amounts of digestible nutrients are only approximately 

 correct, and if assumed for all fodders and conditions, the 

 calculated amounts of nutrients would, in some cases, 



