Dietary Calcium and Phosphorus Levels and the Vitamin D Requirement of the Chick*

IN THE course of experiments on the stability of vitamin D in practical poul-try rations, it was found that the high min-eral content of the rations masked any effect of different levels of vitamin D. The present experiments were under-taken therefore, to study the influence of the calcium and phosphorus content of the diet on the vitamin D requirement of the chick. Bethke et al. (1929) studied the effect of varying the Ca:P ratios in chick diets con-taining no vitamin D. They were able to grow chicks to 13 weeks of age on vitamin D-free diets but growth was poor and the incidence of leg weakness was high. There was some indication that at favorable Ca:P ratios, increasing the level of mineral fav-ored growth and calcification. Hart et al. (1930) confirmed the results of Bethke et al., and grew chicks to 12 weeks of age on vitamin D-free diets. Again the growth was poor and calcification not very satisfactory. It was concluded that "with a minimum supply of vitamin D the levels of calcium and phosphorus in the ration must be higher than in its presence, if growth and calcification are to approach that secured with a generous supply of vitamin D." Couch et al. (1935) indicated that chick