Hypophosphatemic Rickets in Rheas (Rhea americana)

Rickets was diagnosed in 11 rheas from four flocks in Ohio. At necropsy, birds had pliable bones with prominent valgus or varus deformation of the femoral bone and/or the tibiotarsal bone, marked thickening of the metaphyseal plates, and frequent fractures. Histopathologically, bones of rachitic birds showed marked retention of cartilage core within the growth plate, mainly because of a significant lengthening of the hypertrophied zone of the growth plate in relationship to the remaining zones. Feed analysis showed that rachitic; birds were fed diets having higher calcium/phosphorus (Ca/P) ratios (1.38-4.32) than that of the diet fed to nonrachitic birds from a different flock (0.65 Ca/P ratio). Serum analysis of blood from clinically rachitic birds from the affected flocks revealed a marked hypophosphatemia (3.0-4.7 mg/dl), mild hypocalcemia, and normal 25-(OH)-vitamin D concentrations as compared with values in nonrachitic birds, which had serum phosphorus concentrations of 8.5-8.7 mg/dl. These findings suggest that rickets in growing rheas was associated with marked hypophosphatemia and improper Ca/P ratios.