324 THE FEEDING OF ANIMALS 



We are led to the reasonable conclusion that, outside the 

 building of milk solids, a large expenditiu-e of food energy 

 is required to sustain the work of additional food con- 

 sumption, the increased metabolic cell activity and 

 warming of the extra water and food, which are necessarily 

 involved in milk secretion. This view is sustained by the 

 results of investigation. In experiments by the writer 

 with two cows in full flow of milk, which made only a 

 slight gain in body weight, the energy of the digestible 

 part of the rations and of the milk was determined. The 

 figiu-es reached were approximately as follows: 



Table LXIX 



Cow 10 Cow 12 



wt. 775 lbs. wt. 1,200 lbs. 



Calories Calories 



Energy of digested nutrients . . . 27,120 31,300 



Energy of milk solids 8,460 10,200 



Energy not used in milk 18,670 21,100 



Maintenance needs of non-productive 

 animal ... 10,100 13,700 



Balance of energy not accounted for 8,570 7,400 



This energy not accounted for, amounting with the 

 two cows to more than one-fourth the total energy of 

 the nutrients digested, may properly be charged to the 

 work of milk production, including of course, food appro- 

 priation. Science and practice agree in naming 15.5 to 

 16.5 pounds of digestible organic matter as approximately 

 the proper daily amount of digestible nutrients for eco- 

 nomical milk production with a productive cow of aver- 

 age size, much less than which is not to be considered as 

 generous feeding. The necessary supply of nutrients will 

 vary according to the size and productiveness of the cow. 

 Productivity independent of size is a controlling factor. 



