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



yellow would accordingly indicate a fairly well colored to light col- 

 ored butter, between 20 and 8 units of yellow would be called light 

 to very light colored butter, while below these limits ranging down 

 to i or 2 units of yellow would be called white to "dead" white, 

 especially if the fat was still in the form of butter. 



Experiment i. 



The ration of Cow No. 57, a pure bred Jersey, was changed 

 from a ration rich in carotin and xanthophylls to a ration containing 

 a very small amount of these pigments. The ration rich in carotin 

 and xanthophylls consisted of alfalfa hay and yellow corn. The ration 

 poor in these pigments was composed of bleached clover hay and 

 white corn. The results of the experiment are shown in Table n. 



The change from a ration rich in carotin and xanthophylls to 

 one poor in these pigments caused the color of the butter fat to drop 

 from 43 units of yellow to 8.5 units of yellow, from a well colored 

 to a very light colored fat. This change of color was very gradual 

 and required 29 days. It should be stated, however, that the cow 

 did not relish her non-pigmented ration. She lost weight regularly, 

 and her milk production fell off a great deal. It was apparent that 

 the animal was drawing heavily during this entire period from a 

 storage of pigment in her body. It will be shown in the subsequent 

 papers of this series that in this experiment the blood and also the 

 body fat were supplying the pigments for the milk fat. 



It may be stated that a slow lowering of the color of the milk 

 fat, such as took place in this experiment, would be normal for all 

 Jersey cows whose ration is changed to an unpalatable, non-pigmented 

 one like that used in this experiment. The explanation for this is 

 found in the high color of the body fat of this breed of cows. We 

 therefore have here a clear explanation of why Jersey cows will some- 

 times apparently give yellow milk fat during the winter months when 

 their food is almost or entirely lacking in carotin and xanthophylls. 

 Under these conditions if the body fat is called upon to supplement 

 the digestion products of the food in the production of milk fat at 

 the same time the blood serum storage of pigments is being drawn 

 upon, it is clear that the reduction in color of the milk fat will be very 

 gradual, as in the case of Cow No. 57, and a complete elimination of 

 color may require a long period of time. 



Continuing the discussion of the experiment it is seen that when 

 the color of the milk fat had dropped to 8.5 units of yellow the white 

 corn in the ration was replaced by mixed corn, white and yellow 



