Muscle: Bone ratios in beef rib sections

Thirty-eight steers and thirty heifers (14 to 17 months of age, from F(1) Hereford × Brahman cows bred to Angus or Hereford bulls), were either forage-fed for 123 days on millet-bermudagrass pasture or grain-fed for 90 days on a high-concentrate diet and were then commercially slaughtered. Warm carcass weights ranged from 167·8 kg to 324·3 kg. At 24 h post mortem, Texas Agricultural Experiment Station personnel (1) assigned scores or took measurements on each carcass for all factors used in yield grading and quality grading, (2) measured the length of hind leg (HL) and carcass length (CL) and (3) assigned a score for carcass muscling (MS) and, as appropriate, made an adjusted longissimus muscle area (ALA) evaluation. The 9th-10th-11th rib section from one side of each carcass was physically separated into longissimus muscle, fat, 'other soft tissue' and bone and ether extract determinations of the longissimus muscle and 'other soft tissue' components were made and used to adjust the yields of each of these components to a fat-free basis. Muscle to bone ratios ranged from 2·38 to 4·37. With both age and carcass weight held constant, diet, breed and sex explained only 35·8% of the variation in muscle to bone ratio. The best simple correlation with muscle to bone ratio was ALA/CL (r = ·59). Other measures significantly correlated with muscle to bone ratio included ALA (r = 0·55), MS (r = 0·50) and carcass weight (r = 0·49). Multiple regression analyses identified a three-variable subset comprised of ALA, carcass weight and CL which was related (P < 0·01) to muscle to bone ratio R(2) = 0·41). Data suggest that muscle to bone ratios differ widely among beef carcasses of similar genetic-management history and that there are carcass measures useful for predicting muscle to bone ratio.