Here in WI, commercial classes of heifers consist of a breeding animal of no specific breed or % of a breed (ie Shotthorn plus, Comp. Char, etc.). All these animals are thrown into the "commercial" class, which is shown by weight. The champion COMMERCIAL breeding heifer competes against all the other breeds for supreme champion heifer.. ie the champion Angus, Simm, Char Comp, basically any breed represented. COMMERCIAL classes are where your Monopoly, BIM, MAB, etc. calves are put into. These are calves still judged as a breeding piece.
MARKET HEIFERS are again classed by weight. These are heifers judged just like a steer would and in no way judged as a breeding animal. They compete with the STEERS in champion drive.
COMMERCIAL- compete with all other breeds of breeding heifers in the champion drive.
MARKET HEIFERS- Compete with steers in final drive.