CAROTIN, THE PRINCIPAL YELLOW PIGMENT OF MILK FAT 377 



without causing the animal to draw upon any storage of pigment 

 other than the normal one of the blood serum. The result was that 

 the color of the milk fat dropped from 46 units of yellow to 6 units 

 of yellow in twelve days, whereas in Experiment I it required thirty 

 days to bring about a similar change of color. The very low color 

 of the fat which was reached in Experiment 6 also indicates that 

 only the normal storage was being drawn upon. Experiment 6 also 

 shows that corn silage is not a source of pigment for the milk fat. 

 The chemical changes which take place in this roughage evidently also 

 largely destroy the carotin and xanthophylls. The chemical studies of 

 the pigments of corn silage, which were reported above, showed this to 

 be the case. 



RELATION BETWEEN COLOR OF MILK FAT AND BREED OF COW. 



The foregoing experiments have shown conclusively that dairy 

 cows, exclusive of breed, are dependent on the carotin and xanthophylls 

 in their feed for the pigment of their milk fat, in other words, that 

 they cannot produce the pigment which is thus secreted. The ques- 

 tion is at once raised as to wherein lies the so-called breed character- 

 istic which is so much emphasized by the breeders of Guernsey and 

 Jersey cattle? It will not be denied that a breed characteristic does 

 exist in connection with the color of butter fat. We believe, how- 

 ever, that the data now to be presented will show that this breed 

 characteristic has been overemphasized. 



Since the butter fat is dependent upon the food of the cow for 

 its color, it was necessary to compare the color of the butter fat 

 of the different breeds under comparative feeding conditions, in order 

 to obtain a correct estimate of the breed relation. 



It would naturally be expected that the most favorable condition 

 for studying the accuracy of the views held by the cattle breeders and 

 others that some breeds of cows, such as the Jersey and Guernsey, 

 are color producers while other breeds, such as the Holstein, are not 

 color producers would be a comparison of the color of the combined 

 fat of several cows of each breed. Table 17, which follows, gives 

 such a comparison taken from animals in one herd. The milk and 

 fat production of the various cows varied widely. The comparison 

 was made during the winter months, the only source of pigment being 

 a more or less variable quantity of green alfalfa hay in the ration, 

 which was, however, the same for all the animals. 



