512 NUTRITION OF FARM ANIMALS 



If there were available definite knowledge regarding the net 

 energy values of feeding stuffs for milk production, the fore- 

 going figures for the total energy of the milk would serve 

 as a basis for estimating the net energy supply required for 

 the production of a given yield of milk for any one of the 

 ten grades, 25 pounds of 4 per cent milk, for example, requiring 

 336 X 25 = 8400 Cals. of net energy in the feed. 



605. Equivalent energy values for fattening. In the ab- 

 sence of determinations of the net energy values of feeding stuffs 

 for milk production (588) it is impossible to make direct use, in 

 the manner just indicated, of the foregoing data regarding the 

 energy content of milk. Pending such determinations, however, 

 it appears possible to estimate the net energy requirements in 

 the feed of dairy cows in another way, viz., by computing from 

 the composition of the milk, in the manner already described 

 (593), the amount of fattening which is equivalent in energy 

 requirement to a unit of milk yield. Thus it was estimated, 

 on certain assumptions, that the amount of feed energy required 

 for the production of one pound of average 4 per cent milk would, 

 if applied to fattening, have produced a gain of only 252 Cals. 

 in place of the 336 Cals. actually present in the milk. Accord- 

 ingly, a ration containing, in excess of maintenance, 252 Cals. 

 of net energy for fattening would have been adequate to pro- 

 duce a pound of milk containing 336 Cals. of energy. In 

 this way the amount of net energy required for the production 

 of one pound of milk of each of the grades included in the 

 previous table may be computed. 



By this device of reducing the total energy content of the milk 

 to the equivalent amount of net energy for fattening, it appears 

 possible to utilize the net energy values of feeds obtained by 

 Kellner and others in maintenance or fattening experiments 

 as a basis for computing rations for milk. Such a method is, of 

 course, provisional, and the basis for it at present is somewhat 

 slender, but it seems the best one now available. In its actual 

 use for computing rations, however, it appears necessary also 

 to take into account the fact shown by Eckles (722) that with 

 well-fed cows the digestibility of the rations is on the average 

 some 5 per cent lower than the average digestion coefficients 

 which are used in computing net energy values. Accordingly, 

 the figures for the equivalent energy for fattening as computed 



