The Effect of Sex and Age on Bone Morphology and Strength in the Metacarpus and Humerus in Beef-Cross-Dairy Cattle

SIMPLE SUMMARY: Bone strength in long bones is dependent on the strain it is exposed to via the forces from locomotion and bodyweight. The two strategies to increase bone strength (and reduce strain) are increasing either bone size or bone density. However, puberty initiates growth plate closure and, after puberty, most bone growth ceases. In many species, sex and age affect the relationship between bone strength and liveweight. The aim of this study was to examine how bone strength in two different limb bones was affected by age and sex in beef-cross-dairy cattle. The metacarpus and humerus was collected at time of slaughter and scanned using a peripheral quantitative computed tomography (pQCT) scanner to obtain measures of bone size and morphology from three cohorts of beef-cross-dairy cattle. Age, sex and live weight were also recorded. Live weight was the main predictor of bone size and strength, but age and sex influenced this relationship. This was reflected in heifers having a metacarpus that was shorter with less cross-sectional area and bone content than steers of the same liveweight and limited differences between steers and bulls of the same liveweight. At the same bone size older animals were heavier demonstrating an effect of age on bone maturity. ABSTRACT: In cattle, limited data have been reported about the relationship between live weight, bone size, and strength and how this relationship can be altered by factors such as sex and age. The aim of this study was to describe the relationship of peripheral quantitative computed tomography (pQCT)-derived parameters of bone strength and morphology with live weight, age and sex in beef-cross-dairy cattle. All animals were weighed the day before slaughter. The metacarpus and humerus were collected at slaughter and scanned at the mid-diaphysis using pQCT. Live weight was the primary explanatory variable for bone size and strength in all cohorts. However, the effect of age was significant, such that magnitude of response to liveweight was less in the 24-month-old cohort. Sex was significant within cohorts in that bulls had a shorter metacarpus than steers and heifers had a shorter metacarpus than steers at age of slaughter.