Estimation of carcass chemical composition in beef-on-dairy cattle using dual-energy X-ray absorptiometry (DXA) scans of cold half-carcass or 11th rib cut

The aim of the present study was to estimate the chemical composition (water, lipid, protein, mineral, and energy contents) of carcasses measured postmortem using dual-energy X-ray absorptiometry (DXA) scans of cold half-carcass or 11th rib cut. One hundred and twenty beef-on-dairy (dam: Swiss Brown, sire: Angus, Limousin, or Simmental) bulls (n = 66), heifers (n = 42), and steers (n = 12) were included in the study. The reference carcass composition measured after grinding, homogenization, and chemical analyses was estimated from DXA variables using simple or multiple linear regressions with model training on 70% (n = 84) and validation on 30% (n = 36) of the observations. In the validation step, the estimates of water and protein masses from the half-carcass (R2 = 0.998 and 0.997; root mean square error of prediction [RMSEP], 1.0 and 0.5 kg, respectively) and 11th rib DXA scans (R2 = 0.997 and 0.996; RMSEP, 1.5 and 0.5 kg, respectively) were precise. Lipid mass was estimated precisely from the half-carcass DXA scan (R2 = 0.990; RMSEP = 1.0 kg) with a slightly lower precision from the 11th rib DXA scan (R2 = 0.968; RMSEP = 1.7 kg). Mineral mass was estimated from half-carcass (R-2 = 0.975 and RMSEP = 0.3 kg) and 11th rib DXA scans (R2 = 0.947 and RMSEP = 0.4 kg). For the energy content, the R2 values ranged from 0.989 (11th rib DXA scan) to 0.996 (half-carcass DXA scan), and the RMSEP ranged from 36 (half-carcass) to 55 MJ (11th rib). The proportions of water, lipids, and energy in the carcasses were also precisely estimated (R2 >= 0.882) using either the half-carcass (RMSEP <= 1.0%) or 11th rib-cut DXA scans (RMSEP <= 1.3%). Precision was lower for the protein and mineral proportions (R2 <= 0.794, RMSEP <= 0.5%). The cattle category (sex and breed of sire) effect was observed only in some estimative models for proportions from the 11th rib cut. In conclusion, DXA imaging of either a cold half-carcass or 11th rib cut is a precise method for estimating the chemical composition of carcasses from beef-on-dairy cattle. Phenotyping the chemical composition (water, lipid, protein, and mineral contents) of carcasses allows for an understanding of bovine growth physiology and could be used in commercial slaughterhouses to determine the commercial values of carcasses. Owing to the present investigation, dual-energy X-ray absorptiometry scans of a cold half-carcass or 11th rib cut were calibrated as accurate and precise methods for estimating carcass chemical composition in a fast, reproducible, and nondestructive way. Assessment of the water, lipid, protein, mineral, and energy contents of beef carcass allows for an understanding of the bovine growth physiology and is key to determining the carcass's commercial value at the slaughterhouse. Direct measurement of the carcass chemical composition requires postmortem grinding and homogenization of a half-carcass to perform chemical analyses. This reference method is expensive, time-consuming, and destructive of edible meat. The aim of the present study was to develop an alternative and nondestructive method to determine carcass chemical composition based on image scans obtained using dual-energy X-ray absorptiometry (DXA). Equations were calibrated to estimate the carcass composition based on the DXA scans of a whole half-carcass or a single-rib cut in an accurate, precise, fast, and reproducible way. These were established for seven types of beef-on-dairy cattle of different sexes and breeds of sire, which are among the most commonly used in specialized beef-on-dairy fattening production systems worldwide.