274 EXPERIMENT STATION RECORD. 



time these pigments are liept out of the feed, and also very probably in pro- 

 portion to the amount of milk fat being produced. 



" If feed rich in carotin and xanthophylls is given to a milk-giving co\v 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 feed. Fresh green grass probably being the richest in carotin of 

 all natural dairy cattle feeds, accordingly produces the highest colored butter. 



" There is some difference among the 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 feed. Under some con- 

 ditions, 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 the feed, etc. Under normal conditions cows of all breeds pro- 

 duce very high colored jnilk fat for a short time after parturition. The pig- 

 ments 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 

 Burrounding the secretion of the milk of the freshening animal." 



IT. The pigments of the body fat, corpus luteum, and skin secretions of the 

 coto (pp. 211-221). — In these studies it was found that "the yellow lipochrome 

 of the body fat, corpus luteum, and skin secretions of the cow, like the lipo- 

 chrome of butter fat, is composed principally of carotin, which sometimes has 

 associated with it one or more minor xanthophyll constituents. The carotin and 

 xanthophyll pigments of the body fat are derived from the feed of the cow. 

 The body fat of Jersey cows formed on a ration deficient in carotin and xantho- 

 l-hylls is devoid of color. 



" The body fat of Jersey and Guernsey cows is usually characterized by a 

 liigher yellow color than the body fat of other breeds. This is of great im- 

 port;ince in explaining why Jersey and Guernsey cows sometimes show a much 

 slower elimination of pigment from the milk fat on a nonpigmented ration, as 

 during the winter months. In these cases the body fat furnishes a supple- 

 mentary source of carotin and xanthophylls for the milk fat. The yellow body 

 fat of the Jersey and Guernsey cows should not be a point against the use of 

 these animals for beef. The pigments here are the same as those for which the 

 consumer will pay a higher price when present in butter. 



" The bree<lers of Jersey and Guernsey cattle are no doubt correct in their 

 belief that the yellow skin and skin secretions of these animals are character- 

 istic of these breeds. It is not correct, however, that this characteristic is 

 indicative of the ability of the breeds to secrete yellow milk fat under all 

 conditions. The only indication of this is whether the feed contains an abun- 

 dance of carotin and xanthophylls. The blood serum of the new-born Jersey 

 calf is free from carotin and xanthophylls. The small amount of fat on the 

 body is tinted faintly with these pigments." 



III. The yellow lipochrome of blood serum (pp. 223-236). — "The well-known 

 lipochrome of the blood serum of the cow is, like the lipochrome of the milk 

 fat, body fat, etc., of the same animal, composed principally of carotin, the 

 widespread hydrocarbon pigment of plants. Associated in small quantity with 

 the carotin of tlie serum, probably dissolved in the fat of the blood, are one or 

 more xanthophyll pigments which are always found in more or less variable 

 quantity associated with the carotin of plants. The carotin and xanthophylls 



