Estimation of crossbreed beef half-carcass chemical composition by dual-energy X-ray absorptiometry (DXA) scan of half-carcass or 11th rib

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إنجليزي. The aim was to estimate beef cold half carcass (CHC) composition from dual X-ray absorptiometry (DXA) scans of either CHC or 11th rib. Forty-two left CHC (94±49 kg, 17 to157 kg) and their 11th rib were obtained from bulls of the three most Swiss-widespread crossbreeds in dairy herds (♀ Brown Swiss x ♂ Angus, Limousin or Simmental). Lean, fat, bone mineral content (BMC) and total masses of CHC and 11th rib were determined with a DXA scanner (iLunar, GE, “Right Arm” mode). CHC was then grinded, before chemical analyses (lipid: Soxhlet, protein: Dumas, ash: 550°C). Regressions (R software, v3.6.3) were tested between the CHC and 11th rib DXA variates and CHC chemical composition. Cold half carcass contained 11±8.3 (0.8 to 29.1) kg lipid, 18±9.2 (3.1 to 30.6) kg protein and 4±1.8 (0.8 to 6.5)kgash.The CHC weight explained a large part of chemical component masses (lipid:R²=0.884, residual coefficient of variation (rCV)=25.3%; protein R²=0.996, rCV=3.4%; ash R²=0.971, rCV=7.8%). It was also well estimated from CHC DXA total mass with a R2of 0.999(rCV=1.3%). Estimations of lipid, protein and ash masses with a single CHC DXA variate were precise with fat (R²=0.983, rCV=9.7%), lean (R²=0.996, rCV=3.4%) and BMC (R²=0.975,rCV=7.8%), respectively. Multiple models were even more accurate with CHC DXA fat, lean and BMC masses for lipid mass (R2=0.990, rCV=7.7%), CHC weight and DXA fat mass for protein mass (R2=0.997 and rCV=2.9%), and CHC weight, DXA fat and BMC masses for ash mass(R2=0.979andrCV=7.2%). Multiple regressions for estimations of CHC lipid and protein masses from 11th rib DXA variates provided R2 very close to the previous ones established from CHC DXA scan. None the less, the rCV was twice higher for lipid mass (rCV=14.8%), where as it remained equal for protein mass (rCV=2.9%). Crossbreed effect was rarely significant in models and only improved slightly their accuracy (maximum of +1% for the R2and -1.5% for rCV for CHC lipid mass from 11th rib DXA variates). A single rib cut DXA scan appears to be a promising method to estimate carcass composition in a simple, quick, reproducible, accurate and non-destructive way.