There are three skeletal or frame sizes, Small, Medium, and Large, in the USDA Feeder Cattle Grading System, which was implemented in 1979. Medium frame steers are predicted to weigh 1000-1200 pounds at external fat cover of 0.5 inches, with Small weighing below and Large above that range. Equivalent heifers are predicted to weigh 150-200 pounds less than steers. In general, Small frames are severely discounted, as well as the lower range of Medium-frame heifers. Such cattle gain slower and may produce carcasses either weighing less than desired or, at acceptable carcass weights, with excessive fat.
Smaller cattle are more likely to occur in some strains of British breeds.
Continental breeds and crosses are more likely to be excessive in frame size, and weight. It remains to be seen how price and the new frame sizes will be related. The other part of the USDA system is an evaluation of body thickness, not muscle as often thought, although thickness and muscle are related. Thickness No. 1 is described in the Feeder Standards as slightly thick or thicker, No. 2 is narrow, and No. 3 is narrower.