Aim was to compare dual X-ray absorptiometry (DXA) or smartphone-derived picture for estimating the 11th beef rib tissue composition and intramuscular fat content (IMF). Forty-nine beef-on-dairy crossbred bulls (♀ Swiss Brown × ♂ Angus, Limousin or Simmental) were slaughtered at 519.6±8.5 kg body weight. Left 11th rib was DXA scanned (iLunar, GE Med. Syst., “Right Arm” mode) and DXA total mass, lean and fat proportions were recorded. An open-access computer image analysis method based on smartphone pictures of both faces of the rib was used to estimate the total rib area, from which bone, muscle (longissimus and others) and adipose tissue (subcutaneous, inter- and longissimus intra-muscular) proportions were recorded. As gold standard measures, rib was dissected, and longissimus IMF determined by Soxhlet after acid-hydrolysis. Estimative equations of rib composition from DXA or smartphone data were set-up by linear regressions (R 4.2.2). Rib contained 42.6±3.3% longissimus and 63.5±3.3% total muscles, 12.6±1.8% intermuscular and 18.9±3.0% total adipose tissues, and longissimus 1.6±0.5% IMF. Rib longissimus and total muscle proportions were precisely estimated by DXA [root mean square error (RMSE) 1.7 and 1.3%, R²=0.72 and 0.85], as well as intermuscular and total adipose tissues (RMSE=1.0 and 0.9%, R²=0.69 and 0.90, respectively). Precision was similar for smartphone cranial ribs cross-section estimations (RMSE=1.1, 1.4, 1.0 and 1.1%, R²=0.88, 0.82, 0.64 and 0.86, for longissimus, total muscles, intermuscular and total adipose tissues). Longissimus IMF was estimated less precisely, but still satisfactorily by either DXA or smartphone (RMSE=0.28%, R²=0.58 for both). For smartphone, precision was comparable when based on caudal or the average of both faces. At the exception of intermuscular adipose tissue, crossbreed effect was included (P<0.05) in DXA and smartphone models. A single rib DXA scan or cross-section picture seem promising methods to estimate rib composition in a simple, quick, precise, and non-destructive way.
