REQUIREMENTS OF ANIMALS 583 



limits. ^^''•^^^•^'^^~^*^ The vitamin A requirement for laying hens is estimated as 

 483 I.U./IOO g. food.^*'' On the basis of liver storage, a figure as high as 

 375 I.U./IOO g. food (2,250 /zg. carotene/100 g. ration) was proposed by 

 Bolin el al.^^^ The recommendation of the National Research Council 

 Committee on Nutrient Allowances for Poultry^*^ is that the allowance of 

 vitamin A for growing chicks be set at 266 I.U./IOO g. food. 



The vitamin A requirements of adult chickens, and especially of laying 

 hens, are considerably higher than those for the growing chicks. This is to 

 be expected, since the egg contains a fairly large amount of vitamin A. 

 The suggested levels for vitamin A in the diet for satisfactory nutritional 

 results vary from a low value of 440 to 460 I.U./IOO g. food^^^'^^" to a high 

 figure of 920 I.U./IOO g. food."^^ The requirement for pullets is given as 

 333 I.U./IOO g. food. The level needed for efficient egg production is 833 

 I.U./IOO g. food, and 1000 I.U. if the eggs are to be used for hatching.^^' 

 Ruljin and Bird^^^ give this requirement as 1250.4 I.U. of vitamin A. The 

 recommendation of the National Research Council (Bird et al.^^^) is 440 

 I.U./IOO g. food. Intermediate levels of vitamin A have been recom- 

 mended by several investigators. ^^^-^^'^ In arriving at the recommended 

 daily allowance of vitamin A for adult birds, not only egg-production has 

 been considered, but also hatchability of eggs, survival of chicks, mortality 

 of hens, maintenance of laying hens, maintenance of breeding hens, and 

 liver storage. Heywang^^- found that 551 I.U./IOO g. feed was sufficient 

 for egg production and hatchability in cool weather, but that the require- 

 ment was higher in hot weather. 



Several groups of investigators^^'' ■^^^■^^■* reported that carotene is as ac- 



««3 F. F. Castano, R. V. Boucher, and E. W. Callenbach, /. Nutrition, 45, 131-141 

 (1951). 



984 H. J. Almquist, T. H. Jukes, and W. E. Newlon, Calif. Agr. Extension Circ, 108, 

 1-38 (Aug. 1938). 



S85 M. W. Taylor and W. C. Russell, Poultry Sci., 26, 234-242 (1947). 



886 R. E. Gray and H. E. Robinson, Poultry Sci., 20, 36-41 (1941). 



987 G. F. McClary, V. L. Miller, and G. E. Bearse, Western Wash. Expt. Sta. Bull., 

 Dept. Poultry Husbandry (Dec. 1942), pp. 56-57. 



988 D. W. Bolin, C. E. Lampman, and L. R. Berg, Poultry Sci., 22, 348-353 (1943). 



989 H. R. Bii-d, H. J. Almquist, W. W. Cravens, F. W. Hill, and J. McGinnis, Nutrient 

 Requirements for Domestic Animals. I. Nutrient Requirements for Poultry, Nat. 

 Research Council (U.S.), Agr. Bd., Div. Biol. Agr., Washington, 1954, pp. 1-27. 



990 M. W. Taylor, J. R. Stern, W. C. Russell, and E. Jungherr, Poultry Sci., 26, 243- 

 254 (1947). 



991 M. Rubin and H. R. Bird, Univ. Maryland Agr. Expt. Sta., 65, Bull. A-12, 339-350 

 (1942). 



992 B. W. Heywang, Poultry Sci., SI, 294-301 (1952). 



993 R. M. Bethke, P. R. Record, and O. H. M. Wilder, Poultry Sci., 18, 179-187 

 (1939). 



99* J. B. Reynolds, D. B. Parrish, H. L. Mitchell, and L. F. Pavne. Poultry Sci., 27, 

 182-185 (1948). 



