518 Report of the Department op Animal Husbandry of thh 



impelled to the conclusion that the milk fat which this cow pro- 

 duced while under experimental observation had some other 

 source than either the food fat or the previously stored body fat. 



Did this Milk Fat Come from the Protein or from the 



Carbohydrates ? 



In discussing this question we must confine ourselves to the 

 data obtained for the fifty-nine consecutive days during which a 

 record was kept of the income and outgo of both the nitrogen and 

 fat These data show that in this time 38,8 pounds of fat was 

 found in the milk. If this fat was formed through the metabo- 

 lism of protein, the most generally accepted theory is that urea 

 would be a product of the chemical changes necessary to produce 

 this result. This view being correct, the production of 38.8 

 pounds of fat would, according to several theorizers such as 

 Wolff, Henneberg, Voit and Foster, require a minimum of from 

 75.5 to 95 pounds of protein. As a matter of fact, the nitrogen of 

 the urine during the period under consideration was only 2,417.5 

 grams, equivalent to 33.3 lbs. of protein, assuming protein to be 

 N X 6,25. Osborne's and Ritthausen's results show that N x 6 is 

 probably more nearly correct, which would give 32 pounds of pro 

 tein. If we adopt Henneberg's (also Wolff's) fat factor for pro- 

 tein, viz.: 51.4 per cent, which is the highest suggested, 33.3 

 lbs. of protein would furnish 17.1 lbs. of fat, leaving 21.7 lbs. to 

 be accounted for in some other way. In this fifty-nine days the 

 digested food fat was only 3.3 lbs. and the weight of the cow 

 increased 33 lbs. with the nitrogen balauce slightly against her 

 body. 



It is noteworthy, moreover, that during twenty consecutive days 

 of the fifty-nine, the daily nitrogen in the cow's urine was equiva- 

 lent to only 0.4 lb. of protein, while the average daily production 

 of milk fat was 0.58 lb. Granting that none of this protein was 

 metabolized for maintenance purposes, which is unlikely, it is of 

 itself greatly insufficient to account for the milk fat, as it would 

 theoretically be equivalent daily to not over 0.2 lb. of fat. 



