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

1. Young chicks were used to evaluate the efficacy of 2 new vitamin D3 analogs relative to 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) 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 D3 and 20-epi-19-nor-1 alpha-OH D3 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 D3. The 20-epi-19-nor-1 alpha-OH D3 analog had a lower (P < 0.05) phytate-P releasing activity (45%) than either 1 alpha-OH D3 of 20-epi-19-nor-1,25-(OH)2 D3, which did not differ. 4. A dietary concentration of 10 to 15 micrograms/kg 1 alpha-OH D3 was found to optimize phytate-P utilisation in 2-week-old chicks.