Effect of dietary 1,25-dihydroxycholecalciferol level on broiler performance.

Studies were conducted to evaluate the level of dietary 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] required to decrease the incidence of 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 micrograms/kg 1,25-(OH)2D3. The diet contained, by averaged analyses, 0.73% calcium, 0.74% total phosphorus, and 0.22% phytate phosphorus. There was no treatment effect on body weight or gain: feed at either age. The incidence and severity of TD and the percentage of severe lesions were decreased and bone ash was increased by 6 micrograms/kg 1,25-(OH)2D3 at 3 wk of age. At 5 wk of age, the incidences of TD and severe lesions were decreased when 6 micrograms/kg 1,25-(OH)2D3 was fed. Bone ash was increased by this level in one of the two experiments. Plasma calcium was increased at 5 wk when 9 micrograms/kg 1,25-(OH)2D3 was fed, but there was no treatment effect on plasma dialyzable phosphorus or 1,25-(OH)2D3. The results indicate that 6 micrograms/kg 1,25-(OH)2D3 is effective for decreasing TD under practical rearing conditions.