EFFECT OF DIETARY 1,25-DIHYDROXYCHOLECALCIFEROL LEVEL ON BROILER PERFORMANCE

Studies were conducted to evaluate the level of dietary 1,25-dihydroxy cholecalciferol [1,25-(OH)(2)D-3] required to decrease the incidence o f tibial dyschondroplasia (TD) in male broilers at 3 and 5 wk of age. The birds were reared in floor pens with wood shavings and fed a corn- soybean meal diet supplemented with 0, 3, 6, or 9 mu g/kg 1,25-(OH)(2) D-3. The diet contained, by averaged analyses, 0.73% calcium, 0.74% to tal phosphorus, and 0.22% phytate phosphorus. There was no treatment e ffect on body weight or gain: feed at either age. The incidence and se verity of TD and the percentage of severe lesions were decreased and b one ash was increased by 6 mu g/kg 1,25-(OH)(2)D-3 at 3 wk of age. At 5 wk of age, the incidences of TD and severe lesions were decreased wh en 6 mu g/kg 1,25-(OH)(2)D-3 was fed. Bone ash was increased by this l evel in one of the two experiments. Plasma calcium was increased at 5 wk when 9 mu g/kg 1,25-(OH)(2)D-3 was fed, but there was no treatment effect on plasma dialyzable phosphorus or 1,25-(OH)(2)D-3. The results indicate that 6 mu g/kg 1,25-(OH)(2)D-3 is effective for decreasing T D under practical rearing conditions.