| Four groups of day-old turkey poults were fed a synthetic vitamin D-deficient diet. Poults received weekly, progressively increased oral repletion of: corn oil, group I; vitamin D(,3), group II; 1,25(OH)(,2)D(,3), group III; 1,25(OH)(,2)D(,3) plus 24,25(OH)(,2)D(,3), group IV. Poults were examined for clinical and structural changes of bone and parathyroid glands.;Group II poults (control) did not develop rickets. Group II poults had low plasma levels of 25OHD(,3) and 1,25(OH)(,2)D(,3) indicating that growing turkey poults may require higher levels of vitamin D(,3) than NRC requires.;Groups III and IV had significant mild ricketic changes: elongated proliferating-prehypertrophied zone with irregular distal margin and elevated plasma alkaline phosphatase. Total bone ash calcium and phosphorus levels of group IV were similar to group II but group III values were significantly less than group II. These results suggest that 24,25(OH)(,2)D(,3) synergistically restores bone levels of calcium and phosphorus; thus, it is an important vitamin D(,3) metabolite. These results also suggest that vitamin D(,3) is more effective than 1,25(OH)(,2)D(,3) and that 24,25(OH)(,2)D(,3) provides no synergism in preventing all ricketic changes.;Poults in group I rapidly developed ricketic changes by day 10. In the growth plates of the proximal tibiotarsus, the lengths of the proliferating-prehypertrophied and unmineralized hypertrophic chondrocyte zones increased rapidly in conjunction with a reciprocal decrease in length of the mineralized hypertrophic degenerative zones. This reciprocal exchange occurred faster in the proximal tibiotarsus than in the distal tibiotarsus. Other significant findings included: decreases in bone ash, bone ash (calcium, phosphorus and magnesium), bone length, and body weight. Bone-ash, Ca/P ratios and plasma alkaline phosphatase actively increased. There were normocalcemia, hyper-to-normophosphatemia, parathyroid hyperplasia, and rapid depletion of vitamin D(,3) metabolites. Ultrastructurally, hyperplastic parathyroid chief cells had expanded cytoplasmic volumes, reduced numbers of secretory granules, and tortous, interdigitated plasma membranes. Cartilage matrix vesicles (80-113 nm) and bone matrix-like vesicles (53-133 nm) were seen in all four groups. |
