IX. REQUIREMENTS 163 



and certain metabolic disorders which interfere with the conversion or 

 other utihzation of carotene, leads to an intense deep yellow coloration of 

 the skin and subcutaneous tissues known as xanthosis cutis, which is often 

 difficult to distinguish from jaundice, but produces no acute symptoms or 

 damaging effects on tissues. 



IX. Requirements 



A. OF ANIMALS 

 FRED H. MATTSON 



1. Gekeral Considerations 



Investigations as to the vitamin A requirements of animals have been 

 limited mainly to laboratory animals and species having an economic im- 

 portance. With the exception of the rat, the requirements of even the rou- 

 tinely used species of laboratory animals have not been established with 

 certainty. However, from the more thoroughly investigated species, a com- 

 mon pattern relating the vitamin A requirement of mammals to body size 

 has become apparent. This concept was proposed in 1935 by Guilbert and 

 Hart.^ Studies carried out subsequently by these and other workers have 

 further strengthened this concept. It appears that, for mammals, 24 7 of 

 jS-carotene (equivalent to 40 I.U. of vitamin A) or 20 I.U. of vitamin A per 

 kilogram of body weight is the minimum daily requirement to support 

 growth and prevent gross symptoms of deficiency. For storage, reproduc- 

 tion, and lactation considerably higher reciuirements must be met. The 

 requirements of chickens and turkeys per unit of body weight are higher 

 than those of mammals. 



It will be noted that a double standard has been arrived at, depending 

 on whether vitamin A or carotene is fed. Under the conditions of the bio- 

 logical assay, 3 7 of vitamin A alcohol is equivalent to 6 7 of jS-carotene. 

 This relationship, however, holds only under those specified conditions. 

 When the intake is much in excess of that used under assay conditions, the 

 relative potency of the carotene drops off with increasing levels of intake 

 in both mammals^ and birds.' 



Under practical feeding conditions, a mixture of carotenoids, some of 

 which are precursors of vitamin A, as well as vitamin A itself, are used. In 

 using such a feed, account must be taken of the biological potency of the 



1 H. R. Guilbert and G. II. Hart, /. Nutrition 10, 409 (1935). 



2 II. R. Guilbert, C. E. Howell, and G. H. Hart, J. Nutrition 19, 91 (1940). 



3 R. B. Xestler, J. V. Derby, and J. B. De Witt, J. Nutrition 36, 323 (1948). 



