Bone histomorphometry in 1,25(OH)2D3- and vitamin D3-treated aged laying hens

Aged laying hens at oviposition were given four levels of dietary vitamin D3 and three levels of 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) to determine the effects of the additives on the medullary and endosteal bone. Oxytetracycline hydrochloride labeling and histomorphometry of undecalcified sections were used in the determination of changes in medullary bone and endosteal surface of mid-diaphyseal tibiotarsal bones. Treatment with 1,25(OH)2D3 increased mineralized medullary bone area, endosteal surface length, amount of tetracycline labeling in medullary and endosteal bone, total number of osteoclasts on endosteal and medullary bone, and appositional rate of mineralizing bone. Vitamin D3 increased mineralized medullary bone area and total tetracycline labeling in endosteal bone but decreased endosteal mineral apposition rate. Medullary bone matrix with no mineral was observed only in the group receiving neither supplement. These areas were much larger than typical osteoid seams usually seen in trabecular bone. Both 1,25(OH)2D3 and vitamin D3 were effective in stimulating bone formation and retention of mineral within medullary bone matrix at oviposition.