560 IX. CAROTENOIDS AND VITAMINS A 



content of milks, which depends upon the proportion of green pasturage 

 available to the cattle at various times of the year.*^"'^^^ However, Hibbs 

 et al}^"^ reported that a closer relation exists between the pasture carote- 

 noids and the milk carotenoids than between pasture carotenoids and milk 

 vitamin A. After the initial rise at the start of the pasture season, milk 

 carotenoids follow the change in pasture carotenoids more closely when 

 their level is below 250 Mg-/g- fat than when it is higher; this indicates a 

 maximum response in the milk at the above level. The comparative values 

 for the carotenoid content in the milks of cows during the winter (stall-fed) 

 and summer (pasture-fed) are given in Table 5. 



Similar but less pronounced variations in the vitamin A content in 

 milk, as related to season, may be observed. This is reflected in the vita- 

 min A content of butter at different seasons. Thus, in a nationwide sur- 

 ygy893 Qj^ i\yQ j.Q]g q{ buttcr as a source of vitamin A in the diet in the United 

 States (1947), it was found that the vitamin A content of the total output 

 of butter averaged 15,000 I.U./lb.; that of summer butter approximated 

 17,000 to 18,000 T.U./lb., while the potency of winter butter was, on an 

 average, 10,550 to 11,200 I.U./lb. 



Chanda et al.^''^ and Nylund*^^ reported that seasonal variations occur 

 in the carotenoid and vitamin A content of human milk just as in the case 

 of cattle, according to the availability of green foods. 



d. The Effect of Diet on the Carotenoids and Vitamin A in Milk. The 

 seasonal variation in the carotenoid and vitamin A content of the milk, 

 discussed in the previous section, is a reflection of the effect of seasonal 

 variations in provitamin A intake. 



When the vitamin A intake is increased, there is a'parallel increase in the 

 vitamin A excreted in the milk. When supplementary doses of vitamin A 

 varying from to 4,200,000 I.U./day were given to Holstein and Guernsey 

 cows receiving a diet containing a large amount of alfalfa, a progressive 

 rise in the vitamin A level was noted in the milk fat, as shown in Table 6. 



When vitamin A was given in doses of 4,200,000 I.U. per day, it was 

 found that the butterfat produced had a vitamin A content as high as 331 

 I.U./g.,^^^ which compared with a value of 29.6 I.U./g. in the same group 

 before the supplementation with vitamin A was started. Coincident with 

 the increase in total vitamin A, there w^as a marked and steady decrease of 

 milk carotene, as well as of blood carotene. For a further discussion of the 



89» J. L. Brence and J. A. Nelson, /. Dairy Sci., 34, 960-965 (1951). 



89' C. A. Baumann and H. Steenbock, /. Biol. Chem., 101, 547-560 (1933). 



892 J. W. Hibbs, W. E. Krauss, and C. F. Monroe, ./. Dairy Sci., 32, 955-960 (1949). 



8" U. S. Dept. Agr., Miscell. Bull, No. 636, 1-47 (1937). 



894 G. Nylund, Finska Lakare Sdllsk. Handl. (Helsingfors), 80, 733-766 (1937). 



