CAROTIN, THE PRINCIPAL YELLOW PIGMENT OF MILK FAT 4OI 



data on Cow No. 207, it is to be noticed that the inside fat all had 

 a color equal or greater than the corresponding fat of Jersey Cow 

 No. 2, while the outside fats were uniformly much lighter in color. 

 In explanation of this result it may be said that milk cows are known 

 to lay on fat first on the inside of their body, and we have data to 

 show, not only that this particular Holstein cow normally produced 

 high-colored milk fat under favorable feeding conditions, but also 

 that the laying on of most of the fat, whose color is shown in the 

 table, was during the summer when her ration was largely fresh 

 green grass. 



This does not hold true for Holstein Cow No. 221, for much of 

 her fat was also laid on while on grass. It should be added too 

 that the milk fat of this cow was never known to have a very high 

 color. This was brought out especially in a carrot-feeding experi- 

 ment with this animal which was reported in the preceding paper 

 of this series. The maximum color obtained in that experiment was 

 practically the same as the maximum color found in her body fat. 

 There seems to be a breed characteristic evident here, but owing 

 to the high color readings obtained from Holstein Cow No. 207, it 

 may be due to the individual rather than to the breed. 



Perhaps the most important point brought out by this data is 

 that the color of the body fat of any individual, regardless of breed, 

 laid on under given feeding conditions is practically the same as the 

 color of the milk fat under the same conditions. 



Another point which should be mentioned here, but which will 

 be more readily understood in the light of the results which will 

 be given in a subsequent paper, is that this difference between indi- 

 viduals is not due to lack of carotin in the blood. The amount of 

 carotin in the blood of Cow No. 221 at the time of slaughtering was 

 as great as is found in the blood of a Jersey cow receiving the same 

 feed. 



Our data is not sufficiently extensive to warrant any conclusions 

 as to the normal difference in body fat pigmentation between the 

 different breeds. Very probably it is considerably greater than the 

 normal difference between the milk fat pigmentation of the different 

 breeds. The reason for this is not evident from our present knowl- 

 edge of the physiology of pigmentation. The fact that such a wide 

 difference often does exist is of considerable importance, however, 

 in explaining why the milk fat of Jersey and Guernsey cows often 

 has a higher color than can be explained by the character of the 

 ration. Reference was made to this in connection with the feeding 

 experiments reported in the preceding paper on the milk fat pigment. 



