650 X. VITAMINS D 



There is a sufficient concentration of the provitamins D in milk to render 

 possible a maximum production of 200 I.U. vitamin D/quart, but the com- 

 mercial irradiated milks have been standardized to contain 135 I.U. /quart. 



An additional procedure for increasing the vitamin D in milk, and the 

 most physiologic method, involves increasing the vitamin D intake on the 

 part of the cow. This is usually done by the feeding of limited amounts 

 of irradiated yeast to the animals. When controlled quantities of yeast 

 are given, milk having as much as 400 I.U. /quart is produced. This is the 

 so-called "metabolized" vitamin D milk. Kraus et aZ.'^^-^^^ demonstrated 

 that milk and butter containing increased amounts of vitamin D were 

 produced after irradiated ergosterol (vitamin D2) was administered to the 

 cows; however, Thomas and MacLeod^^'^ and Kraus and Bethke'^^ found 

 that an even greater increase in the vitamin D content of milk resulted 

 when irradiated yeast was fed in place of the irradiated ergosterol. Cod- 

 liver oil concentrate (Vitex), also, has been satisfactorily employed for 

 this purpose. ^^^ Kirk-*"' recorded an increased concentration of vitamin D 

 in the milk of the ewe after feeding irradiated yeast. Irradiated ergosterol 

 exerted less augmentatory effect in this species than it did in the cow. 



In the eggs of birds, vitamin D is usually present in fairly large amounts; 

 it occurs exclusively in the yolk. An average figure for the yolks of hen's 

 eggs is 150 to 400 I.U./IOO g.'^* The vitamin D content in the egg is in- 

 creased when the hen is irradiated, '-'^^ as well as when the food contains an 

 increased quantity of vitamin D.-"'-'-"^ 



In the case of milk and eggs, the increased vitamin D produced by vita- 

 min D feeding is of the same type as that present in the food. Thus, 

 Bethke et al.^^^ reported that, when the vitamin D in the milk was in- 

 creased by feeding irradiated yeast, it required about ten times as much of 

 this vitamin D (presumably vitamin D2) to satisfy the requirement for the 

 chick as was the case when the source of the vitamin D was irradiated milk 

 (presumably vitamin D3 produced by activation of the provitamin D3, 7- 



'96 W. E. Kraus and R. M. Bethke, J. Biol. Chem., 92, x-xi (1931). 



'"« W. E. Kraus, R. M. Bethke, and C. F. Monroe, J. Nutrition, 5, 467-477 (1932); 

 Ohio Agr. Expt. Sta. Bimonthly Bull., No. 156, 117-121 (1932). 



1" B. H. Thomas and F. L. MacLeod, Science, 73, 618-620 (1931). 



158 W. E. Kraus and R. M. Bethke, Ohio Agr. Expt. Sta. Bimonthly Bull, 18, No. 162, 

 77-80(1933). 



199 W. E. Kraus, R. M. Bethke, and M. Wilder, Ohio Agr. Exptl. Sta. Bimonthly Bull., 

 18, No. 1,15-19(1933). 



2"o W. O. Kirk, Iowa State Coll. J. Sci., 13, 235-238 (1939). 



2«i G. H. Maughan and E. Maughan, Brit. J. Phys. Med., 7, 137-138 (1932). 



202 G. H. Maughan and E. Maughan, Science 77, 198 (1932). 



2»3 G. M. DeVaney, H. E. Munsell, and H. W. Titus, Poultry Sci., 12, 215-222 (1933). 



