ENERGY VALUES OF RATIONS FOR FARM ANIMALS. 25 



THE CHOICE OF FEEDING STUFFS. 



When, as in the last example, feeding stuffs must be purchased in 

 order to get the desired relation between the protein and the energy 

 of the ration, it is evident that often a wide range of choice may be 

 offered. In such a case the question at once arises which of the vari- 

 ous feeds available is it most economical to purchase, it being evident 

 of course, that this is not necessarily the one offered at the lowest price. 



No simple method of determining this point is possible, because, 

 as we have seen, the feed serves two entirely distinct purposes in the 

 body. Sometimes the supply of protein is the specially important 

 point, and in other cases what is needed is a supply of energy without 

 special reference to whether its source be protein or nonnitrogenous 

 material. Consequently, the relative values of two feeding stuffs may 

 vary under different circumstances. Some writers have based their 

 comparisons of the values of by-product feeds solely upon their con- 

 tent of protein, for the reason that such feeds are often bought espe- 

 cially to supply this ingredient, while the fats and especially the car- 

 bohydrates are usually produced in abundance upon the farm. They 

 regard that purchased feeding stuff as the most economical which fur- 

 nishes a pound of digestible protein at the lowest cost, ignoring any 

 value hi the other ingredients. It is obvious, however, that this is a 

 one-sided view. The other ingredients have a value, and this is espe- 

 cially true in the case of a feeder who buys a considerable part of his 

 grain supply and depends upon it as a source of energy as well as of 

 protein. The method of comparison illustrated in the following pages 

 is based primarily upon the cost per unit of energy because this is on 

 the whole the most important function of the feed, but the method 

 takes account also of the amount of protein present. 



Let us suppose the following feeding stuffs are available to a dairy- 

 man at the prices named : 



Prices of feeds per ton. 



Oats (40 cents per bushel) $25 



Corn meal 25 



Wheat bran " 21 



Wheat middlings (flour) 24 



Dried brewers' grains 23 



Gluten meal 27 



Cottonseed meal (prime) 30 



Old-process linseed meal 33 



The supply of coarse feed on the farm is sufficient to furnish each 

 animal per day 32 pounds of silage and 8 pounds of clover hay; the 

 cows average 1,000 pounds each and may be expected to produce per 

 day about 24 pounds of milk testing 4.5 per cent fat. 



