The USDA grades for feeder cattle were last revised 20 years ago, with separate consideration for frame size and body thickness. Under those grades, Medium frame steers are projected to finish with inch fat cover at 1000 to 1200 lb.
Small frame is below and Large frame above that range.
Heifers are projected to finish 150 to 200 lb lighter. Not surprisingly, most cattle are No.1 thickness and No.3 is rare. Hearings will be held on these proposals. AFC was moderately heritable, but the heritability of CI was essentially zero. So, selection in heifers may reduce age at first calving, but earlier calving heifers may have longer calving intervals.