166 VITAMINS A AND CAROTENES 



studied. Although normal growth was obtained when the animals were fed 

 vitamin A at a level of 100 LIT. per kilogram of body weight per day, sur- 

 vival time and the reproductive period were extended when the level of 

 intake was increased to 200 I.U. and still more when 400 I.U. were fed. 

 From these results, it would appear that the optimal level of vitamin A in- 

 take may be far in excess of any that have been considered previously. 



McCarthy and Cerecedo^^ place the vitamin requirement of the mouse 

 at 1 I.U. per animal per day. 



3. Rabbits 



Although it is recognized that the rabbit requires vitamin A, few quan- 

 titative data have been obtained on this species. Phillips and Bohstedt^^ 

 have reported that rabbits fed a vitamin A-free diet can be maintained in 

 a satisfactory state of health when supplemented with carotene at a level 

 equivalent to 83 I.U. of vitamin A per kilogram of body weight per day. 



4. Dogs 



Based on the rate of disappearance from the liver, the vitamin A require- 

 ment of the dog has been estimated as being between 23 and 47 I.U. per 

 kilogram of body weight per day.^^ 



5. Foxes and Minks 



One of the characteristics of vitamin A deficiency in the fox is the develop- 

 ment of certain nervous symptoms. Using this syndrome as a criterion, 

 Smith^^ placed the minimum daily requirement of the fox at from 15 to 

 25 I.U. per kilogram of body weight. Storage of the vitamin did not take 

 place until the intake of the vitamin was increased to 50 to 100 I.U. Bas- 

 sett et al.-'^ found 25 I.U. per kilogram of body weight per day to be the 

 minimal level which would allow satisfactory growth and a detectable con- 

 tent of vitamin A in the blood serum. The requirement of the mink, al- 

 though not exactly established, was estimated by the same workers as 

 being somewhat less than that of the fox. 



6. Horses 



The horse was one of the species used in the original work from which the 

 concept of the relationship between body size and vitamin A requirement 

 developed. Using nyctalopia as a criterion, the requirement of the horse was 



16 P. McCarthy and L. R. Cerecedo, Federation Proc. 9, 364 (1950). 



I'' P. H. Phillips and G. J. Bohstedt, J. Nutrition 15, 3()<) (1938). 



18 P. D. Crimm and D. M. Short, Am. J. Phj/siol. 118, 477 (1937). 



i«S. E. Smith, ./. Nutrition 24, 97 (1942). 



20 C. F. Bassett, J. K. Loosli, and F. Wilke, J. Nutrition 35, 629 (1948). 



