Activity of various hydroxylated vitamin D3 analogs for improving phosphorus utilisation in chicks receiving diets adequate in vitamin D3

1. Young chicks were used to evaluate the efficacy of 2 new vitamin D-3 analogs relative to 1 alpha-hydroxycholecalciferol (1 alpha-OH D-3) for their ability to improve the bioavailability of phytate-bound phosphorus (P) when added to P-deficient maize-soyabean meal diets that were superadequate in cholecalciferol. 2. Both 20-epi-19-nor-1,25-(OH)(2) D-3 and 20-epi-19-nor-1 alpha-OH D-3 Were observed to have phytate-P releasing activity, as measured by bone ash responses. 3. However, the bioactivity of the 2 new analogs differed when compared with 1 alpha-OH D-3. The 20-epi-19-nor-1 alpha-OH D-3 analog had a lower (P< 0.05) phytate-P releasing activity (45%) than either 1 alpha-OH D-3 or 20-epi-19-nor-1,25-(OH)(2) D-3, which did not differ. 4. A dietary concentration of 10 to 15 mu g/kg 1 alpha-OH D-3 was found to optimize phytate-P utilisation in 2-week-old chicks.