84 MANUAL OF MILK PRODUCTS 



2. The carotin and xanthophylls of milk-fat are not synthe- 

 sized in the cow's body, but are merely taken up from the food 

 and subsequently secreted in the milk-fat. 



3. When food practically free from carotin and xanthophylls, 

 such as the cow usually receives during the winter months, is 

 given to a milk-giving cow, the immediate supply of these 

 pigments in the organism is greatly depleted and may be entirely 

 used up, on account of the constant drain upon the supply by 

 the milk glands. The butter- fat accordingly approaches a 

 colorless condition in proportion to the supply of carotin and 

 xanthophylls in the system, the length of time these pigments 

 are kept out of the food, and also, very probably, in proportion 

 to the amount of milk-fat being produced. 



4. If food rich in carotin and xanthophylls is given to a milk- 

 giving cow whose milk-fat has become practically colorless by 

 reason of the above conditions, the organism will at once recover 

 its lost pigments and the milk- fat will .increase in color in pro- 

 portion to the amount of carotin and xanthophylls, especially 

 carotin, in the food. Fresh green grass, probably being the 

 richest in carotin of all natural dairy cattle feeds, accordingly 

 produces the highest-colored butter. 



5. There is some difference among different breeds of dairy 

 cows in respect to the maximum color of the milk-fat under 

 equally favorable conditions for the production of a high color. 

 Each breed of cows, however, will undergo the same variation in 

 color of the milk-fat which follows a withdrawal or addition of 

 carotin and xanthophylls, especially carotin, to the food. 

 Under some conditions, also, the apparent breed characteristic 

 largely disappears. The popular opinion in regard to the breed 

 characteristic has been overemphasized, and statements in 

 regard to it should in the future be qualified with a statement 

 of the conditions of feed and the like. 



6. Under normal conditions cows of all breeds produce very 

 high-colored milk-fat for a short time after parturition. The 





