The standards provide for five grades of feeder pigs U.S. No. 1, U.S. No. 2, U.S. No. 3, U.S. No. 4 and U.S. Utilityfor slaughter swine and pork carcasses.
-Last rib back fat
-Muscle score (Thin=1, Average=2, Thick=3)
formular
(4 x last rib fat) –muscle score