Bone Morphology and Strength in the Mid-Diaphysis of the Humerus and Metacarpus in Dairy Calves Prior to Weaning

SIMPLE SUMMARY: Calf growth and nutrition has been thoroughly researched in relation to future milk production. The effect of nutrition on growth has been overlooked, however, and the emergence of humeral fractures in first lactation heifers has driven the need for further research. The aim of this study was to understand the relationship of calf growth with bone measures such as size and density prior to weaning. Liveweight, height, body length, girth and leg length were measured at one, six and twelve weeks of age. At these intervals, the middle of the metacarpus was also scanned using a CT scanner. At the six and twelve weeks measures, a subset of calves were euthanised and the humerus was collected and scanned in the middle of the bone. Differences in growth between the metacarpus and humerus were observed over time. Liveweight was the main driver of the majority of bone measures in both the metacarpus and humerus. The strong relationship between weight and bone shows the importance of adequate preweaning nutrition to ensure adequate future bone growth. ABSTRACT: Calf growth rate in relation to future milk production has been thoroughly studied; however, the observation of growth arrest lines in bones from heifers with humeral fractures has highlighted the need to understand bone growth in relation to calf growth. The aim of this study was to describe the relationship of peripheral quantitative computed tomography (pQCT)-derived measures of bone strength and morphology with gross measurements of size and growth in pre-weaning dairy calves. Liveweight, height, body length, girth and leg length were measured at one, six and twelve weeks of age. At these intervals, the mid-diaphysis of the metacarpus was also scanned in the live animal using pQCT. At six and twelve weeks old, a subset of calves were euthanised and the humerus was collected and scanned at the mid-diaphysis using pQCT. Differences in growth patterns were observed between the metacarpus and humerus over time. Weight was the best predictor for measures of periosteal circumference and stress strain index (R(2) = 0.49–0.58) in the metacarpus, and also the best predictor for measures of stress strain index at all ages in the humerus (R(2) = 0.94). The strong relationship with weight and bone measures emphasises the need for adequate preweaning nutrition for future bone growth.