The mineral composition and microscopic changes in thoracic buttons of Chinese Yellow steer with age.

Tips of sacral, lumbar and thoracic vertebrae were sampled from 67 Chinese Yellow steer carcasses to determine relationships of the mineral composition in tips of vertebrae to the ossification degree as well as the dental age. Thoracic buttons were taken from another 11 Chinese Yellow steer carcasses to study their microscopic changes with age. Percentages of ash, calcium and phosphorus in thoracic buttons, on a fresh weight basis, increased with increasing ossification degree (R(2)=0.9815, 0.9743, 0.9817, respectively) and dental age (R(2)=0.9496, 0.9455, 0.9209, respectively), but those in tips of lumbar and sacral vertebrae varied little (P>0.05). Based on the same levels of ash percent in thoracic buttons, a corresponding relationship between the ossification degree and the dental age was observed: thoracic buttons did not ossify when the dental age was under 24 months; and 10%, 30%, and 40% of thoracic buttons ossified at the dentition-based age of 36, 50, and 60 months. Observations by scanning electron microscopy indicated that cartilages of Chinese Yellow steer thoracic buttons began to ossify at approximately 24 months and ossified completely at 84 months. The present study could be useful to improve the accuracy of age estimation for Chinese Yellow steers in the Chinese beef grading system.