EFFECT OF 1,25-DIHYDROXYCHOLECALCIFEROL, CHOLECALCIFEROL, AND FLUORESCENT LIGHTS ON THE DEVELOPMENT OF TIBIAL DYSCHONDROPLASIA AND RICKETS IN BROILER-CHICKENS

Experiments were conducted to determine whether dietary 1,25-dihydroxy cholecalciferol [1,25-(OH)(2)D-2] will alleviate a cholecalciferol def iciency induced by low dietary cholecalciferol and no fluorescent ligh ting and to determine cholecalciferol requirements as influenced by fl uorescent lighting or 1,25-(OH)(2)D-3. In each study, nutritionally co mplete basal diets were fed to broiler cockerels from 1 to 16 d of age . Experiment 1 had a 2 x 2 x 2 factorial arrangement of treatments wit h 1,25-(OH)(2)D-3 at 0 and 10 mu g/kg, cholecalciferol at 2.75 and 27. 5 mu g/kg, and fluorescent lights on or off. Experiments 2 to 4 had fo ur levels of dietary cholecalciferol (0, 5.0, 27.5, and 50.0 mu g/kg) and fluorescent lights on or off (Experiment 2) or 1,25-(OH)(2)D-3 at 0 and 10 mu g/kg (Experiments 3 and 4). In Experiment 1, fluorescent l ighting increased bone ash, and decreased the incidence and severity o f rickets at 2.75 mu g/kg cholecalciferol and 0 mu g/kg 1,25-(OH)(2)D- 3 and reduced the severity of TD at both levels of cholecalciferol and 0 mu g/kg 1,25-(OH)(2)D-3. In all cases 1,25-(OH)(2)D-3 improved bone ash. The metabolite also decreased the incidence ans severity of TD a t both cholecalciferol levels with lights off and decreased the incide nce and severity of rickets at 2.75 mu g/kg cholecalciferol and lights off. In the absence of fluorescent lighting and 1,25-(OH)(2)D-3 27.5 mu g/kg cholecalciferol reduced the incidence and severity of rickets to levels equivalent to those produced by eith fluorescent lighting or 1,25-(OH)(2)D-3 alone (Experiments 2,3, and 4). However, even 50.0 mu g/kg cholecalciferol was not as effective as fluorescent lights or 1, 25-(OH)(2)D-3 in reducing the incidence and severity of TD.