386 MISSOURI AGRICULTURAL EXP. STA V RESEARCH BULLETIN NO. IO 



SUMMARY. 



1. The fat of cows' milk owes its natural yellow color to the 

 pigments carotin and xanthophylls, principally carotin, the well-known, 

 wide-spread, yellow vegetable pigments found accompanying chloro- 

 phyll in all green plants. 



2. The carotin and xanthophylls of milk fat are not synthesized 

 in the cow's body, but are merely taken up from the food and subse- 

 quently 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 but- 

 ter 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 proportion 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 xan- 

 thophylls, especially carotin, to the food. Under some conditions, 

 also, the apparent breed characteristic largely disappears. The popu- 

 lar opinion in regard to the breed characteristic has been overempha- 

 sized, and statements in regard to it should in the future be qualified 

 with a statement of the conditions of feed, etc. 



6. Under normal conditions cows of all breeds produce very high 

 colored milk fat for a short time after parturition. The pigments 

 of the fat at this time are identical with the normal pigments of the 

 fat. Their increase at this time is probably due to the physiological 

 conditions surrounding the secretion of the milk of the freshening 

 animal. 



