Analytical bone calcium and bone ash from mature laying hens correlates to bone mineral content calculated from quantitative computed tomography scans

Laying hen skeletal health continues to be an industry priority. Bone ash and bone Ca quantification in laying hen long bones provides valuable information on skeletal health. Unfortunately, these measurements can only be accomplished by sacrificing hens, thus making longitudinal measurements on the same hen impossible. Quantitative computed tomography (QCT), used with a calcium hydroxyapatite phantom, has been used to determine bone density of wings and legs as well as live hens throughout the production cycle by scanning with a calcium hydroxyapatite phantom. QCT has also been used to scan live hens throughout the production cycle. The purpose of this study was to determine how QCT calculated bone mineral content (QCT BMC) corresponds to analytical bone Ca and bone ash. Wing and leg quarters from 72-wk-old W-36 hens were QCT scanned along with a QCT Phantom. After scanning, humeri, femurs, and tibias were cleaned, divided into epiphysis (E) and diaphysis (D), fat extracted, ashed, and digested under nitric acid, and Ca was determined by atomic absorption spectroscopy was used to determine E, D, and whole bone Ca. Four bones/type were used for E and D, while 6 bones/type were used for whole bone measurements. A second set of bones were prepared to determine correlation of BMC to bone ash. QCT scans were analyzed with Mimics software (Materialise NV, Leuven, Belgium) to calculate bone volume and density in Hounsfield units. Utilizing the QCT phantom and bone volume, BMC was calculated for E, D, and whole bone. Data were analyzed with regression analysis and Pearson correlation coefficients were determined. Analytical Ca was correlated to QCT BMC for E (R = 0.84, P < 0.01), D (R = 0.99, P < 0.01), and whole bone (R = 0.97, P < 0.01). Whole bone ash was highly correlated to QCT BMC for femur (N = 47, R = 0.97, P < 0.001), tibia (N = 50, R = 0.94, P < 0.001), and keel (N 50, R = 0.94, P < 0.001). Whole bone ash and QCT BMC values of femur and tibia were not different (P = 0.39 and 0.22 respectively). Based on this information, QCT could provide relative quantitative assessment of total bone mineral in live birds proving useful in long-term studies.