Comparison of processed and unprocessed digital images for the determination of radiographic bone aluminum equivalent (RBAE) values in equine bone

Comparison of Bone Mineral Content of the Equine Third Metacarpal to Total Radiographic Bone Aluminum Equivalents From Unprocessed Digital Radiographs

Digital radiographs are common for estimating bone mineral content (BMC) in horses with radiographic bone aluminum equivalents (RBAE). Processing algorithms are used to produce clearer images of digital radiographs in clinical settings, but this distorts RBAE. This study compared RBAE from digital radiographs to BMC from bone ash, and physical and digital morphology measurements. Digital radiographs were taken of six third metacarpals (MCIII) from equine cadavers with an aluminum step wedge penetrometer. A 2-cm transverse section of bone was digitally analyzed and excised from each MCIII. For each image, a linear regression was created using the step wedge thicknesses (R² > 0.99) and used to obtain total and individual RBAE. Outer and inner diameters of both dorsal-palmar (DP) and lateral-medial (LM) aspects, as well as cortical thicknesses, were measured physically and digitally. Bone samples were ether-extracted, oven-dried, and ashed. Statistics were analyzed as correlations between variables. Physical and digital measurements of dorsal, medial, and lateral cortices, as well as DP outer diameter, tended to be similar (r > 0.74, P < .09) but palmar cortex measurements did not (r = 0.41, P = .42). The LM outer and DP/LM inner diameters were similar between the two methods (r > 0.95, P < .05). Total RBAE was strongly correlated to BMC (r > 0.93, P < .01). These results suggest that using digital radiographs to make morphological measurements is accurate and confirm the strong relationship between total RBAE and bone ash. However, this study emphasizes the need to use unprocessed radiographs for analysis.

Influence of Long-Term Furosemide Use on Bone Mineral Content, Bone Metabolism Markers, and Water Weight Loss in Horses

Furosemide is used to reduce the incidence of exercise-induced pulmonary hemorrhage in racehorses. Previous research suggests furosemide negatively impacts calcium balance, which may have long-term implications for bone health. Eleven healthy horses, either control (CON, n = 5) or treatment (FUR, n = 6), were used to test furosemide's effects on bone mineral content (BMC), bone metabolism biomarkers, and weight loss after administration. Treatment horses received IV furosemide at 1 mg⋅kg^-1 BW once weekly for seven weeks, and blood was collected before and at 24 hours after administration for biomarker analysis. All horses were weighed before and at 2, 4, 8, 24, and 48 hours after administration. Radiographs of the left third metacarpal were taken every 28 days for BMC determination using radiographic bone aluminum equivalence. After administration, FUR lost more BW than CON (P < .05 for all) as quickly as 2 hours after administration (CON: -0.4 ± 0.3%, FUR: -2.2 ± 0.3%), and these losses remained greater than CON at 4 hours (CON: -1.0 ± 0.3%, FUR: -3.3 ± 0.3%) and 8 hours (CON: 0.0 ± 0.3%, FUR: -1.2 ± 0.3%). FUR lost more BW on day 0 than CON (P = .03), but on day 28 and day 49, FUR BW losses were no greater than CON (P > .10). No treatment effects were observed for BMC nor pyridinoline and osteocalcin concentrations (P > .10). Reduced BW changes over time in FUR but not CON warrant further investigation to establish the efficacy of frequent furosemide administration over long periods of time.