Histomorphometry and vitamin D metabolism of valgus-varus deformity in broiler chickens.

Vitamin D metabolite levels and tibiotarsal histomorphometric characteristics were determined in 49-day-old male broilers. Valgus-varus bone deformity was present in 5.2% and tibial dyschondroplasia (TD) in 3% of these broilers, which were raised on floor litter under seemingly normal nutritional, space, and lighting conditions. No significant weight differences were observed between normal and lame broilers. The plasma levels of 25-OH-D were the same in lame and normal broilers. However, 1,25-(OH)2D plasma levels were reduced 28% in broilers with valgus-varus deformities but normal in broilers with TD. Anatomically, there were three different patterns of bone development in the undecalcified mid-diaphyseal sections. The pattern with the least periosteal growth, lowest tetracycline labeling, and smallest marrow cavity was most often seen in valgus-varus deformities. Patterns with greatest periosteal growth, high tetracycline labeling, and larger marrow cavities were more representative of normal broilers. It was hypothesized that defective prostaglandin metabolism reduced 1,25-(OH)2D levels, contributing to the overall reduction in bone formation and bone resorption observed in broilers with valgus-varus bone deformity.