The effects of 1,25-dihydroxycholecalciferol on performance and bone development in the turkey poult

The effect was studied of 1,25-dihydroxycholecalciferol [1,25-(OH)2 D3] at various levels of vitamin D3, with adequate or inadequate dietary calcium, on performance and bone development in turkey poults. Two experiments were conducted. Experiment 1 lasted 16 days and was a 4 × 2 factorial arrangement using a low calcium diet (.7%), with dietary levels of vitamin D3 of 450, 900, 1,800, and 3,600 ICU/kg of diet and with or without 10 μg of dietary l,25-(OH)2 D3. Experiment 2 lasted 14 wk and was a 2 × 2 × 2 factorial arrangement with vitamin D3 levels of 900 or 2,700 ICU/kg of diet, calcium levels at 58 or 100% of the National Research Council requirement (which varies with age), and with or without 10 μg/kg of dietary l,25-(OH)2 D3. In Experiment 1, increasing levels of vitamin D3 and l,25-(OH)2 D3 supplementation significantly increased bone ash. Pairwise contrasts at specific vitamin D3 levels indicated that this effect of l,25-(OH)2 D3 was greater at lower levels of vitamin D3. In Experiment 2, the 2,700-ICU level of vitamin D3 decreased the incidence of rickets at 3 wk and partially ameliorated a calcium deficiency, as indicated by an increase in growth at the 2,700-ICU level of vitamin D3 in calcium-deficient diets from 8 to 14 wk. Vitamin D3 by calcium interactions on rickets at 14 wk of age and bone ash at 3 and 14 wk were similar and indicated also that vitamin D3 partially ameliorated a calcium deficiency. In general, the addition to the diet of 1,25-(OH)2 D3 increased bone ash and decreased the incidence of rickets in diets deficient in calcium but high in vitamin D3. There is very little evidence in the present study that indicates that 1,25-(OH)2 D3 has any effect on tibial dyschondroplasia.