QUANTITATIVE REQUIREMENT FOR CHOLECALCIFEROL IN THE ABSENCE OF ULTRAVIOLET-LIGHT

Studies were conducted to determine the basic requirement of the bird for cholecalciferol in the absence of ultraviolet light by utilizing f ilter sleeves on fluorescent lights in the room and brooder. In Experi ment I, some pens were fitted with filter tubes and some lights were t urned off. All the birds received a cholecalciferol-deficient diet. Bi rds with ultraviolet light excluded grew slowly, developed rickets (95 %), had low plasma calcium, and low bone ash (27%); whereas birds expo sed to the fluorescent light had normal growth and plasma calcium, sli ghtly low bone ash (38%), and some rickets (12%). Experiments 2 and 3 were conducted to determine the amount of cholecalciferol that must be added to the diet under conditions in which ultraviolet light was exc luded. In Experiment 2, the highest level of cholecalciferol fed was 4 00 ICU/kg. This level was not sufficient to permit the chickens to hav e weight gain or bone ash equal to the birds receiving the ultraviolet light. The birds receiving 400 ICU/kg of diet also had a 77% incidenc e of rickets compared with 20% for the birds receiving ultraviolet lig hts. In Experiment 3, when birds received 800 or 1,600 ICU/kg of chole calciferol in the diet, they grew and were comparable to those receivi ng ultraviolet light for the criteria measured.