520 NUTRITION OF FARM ANIMALS 



by-products containing a minimum of fat, may a favorable 

 effect upon the yield of milk and its percentage of fat be antici- 

 pated from an increase in the supply of digestible fat. 



614. Influence on utilization of energy. None of the ex- 

 periments on the influence of the fat supply upon milk production 

 afford any exact data regarding the concurrent gain or loss of 

 tissue, since no determinations of the gaseous excreta were made. 

 It is impossible, therefore, to determine whether the observed 

 effect of the feed fat was brought about by a stimulation of milk 

 production at the expense of fattening, i.e., by modifying the 

 direction in which the energy of the feed was utilized, or whether, 

 under its influence, the metabolism in the milk gland was actu- 

 ally effected more economically. 



Ash requirements for milk production 



Practically no data are on record upon which a trustworthy 

 estimate of the ash requirements of the dairy cow can be based. 



615. The outgo in the milk. It is true that the outgo of 

 mineral elements in the milk may be determined without special 

 difficulty and that reasonably accurate figures are available 

 from which it may be estimated. This, however, is but a single 

 element in the problem. It became evident in considering the 

 ash requirements for maintenance in Chapter IX (421-436) 

 and those for growth in Chapter XI (492-497) that neither the 

 actual availability of the mineral elements of feeding stuffs 

 nor the influence of the amount and quality of the ash supply 

 upon the losses in feces and urine has been sufficiently investi- 

 gated to permit any satisfactory conclusions as to the influence 

 of these factors. 



Kellner 1 has, however, computed the approximate require- 

 ments for calcium and phosphorus from the outgo in the milk. 

 Accepting Henneberg's estimate of 71.4 grams of calcium and 

 21.8 grams of phosphorus per 1000 kilograms live weight for the 

 maintenance requirements, he adds to these three times the 

 average amounts found in the milk upon the somewhat ques- 

 tionable assumption that only one-third to one-half the feed 

 ash is available. Computed for a yield of 20 pounds of milk 

 per day by a thousand pound cow, his results are as follows : 



1 Ernahrung landw. Nutztiere, 6th Ed., p. 595. 



