Changes in the Outer Shape, Inner Structure and Bone Mineral Density of the Tibia in Growing Japanese Quail, Coturnix japonica

The length, width and thickness of cortical bone at the central diaphysis, as well as the inner structure and bone density in the tibia of growing Japanese quail (Coturnix japonica) were examined from hatching to 100 days of age at 10-day intervals to investigate long bone growth in quail. The body weights were also measured. Five left tibiae in male and female quail were evaluated, respectively. The inner structure of the tibia was observed on enlarged transparent X-ray images. The bone mineral densities at the proximal epiphysis and central diaphysis were estimated by the hydroxyapatite density using the SXA method. The female weight exceeded the male weight, and a significant sexual difference was observed after 40 days of age. There were no significant differences between the sexes for the length, width and thickness of cortical bone in the central diaphysis. The length, width and thickness of cortical bone stopped increasing at 40, 60 and 30 days of age, respectively. In male and female quail, the growth plates in the distal and proximal epiphyses disappeared at 30 and 40 days of age, respectively. The medullary cavity in the female tibia became bright from 40 days of age when the female quail began to lay eggs, and this was considered to represent medullary bone. The bone mineral density at the proximal epiphysis in the male tibia stopped increasing at 40 days of age, whereas that in the female tibia continued to increase until 100 days of age. The female bone mineral density at the diaphysis significantly exceeded the male value from 10 to 100 days of age. From these results, we conclude that the heavy body weight and presence of medullary bone in the medullary cavity in the female tibia raised the bone mineral densities at the proximal epiphysis and central diaphysis.