The economically important carcass and live traits in swine are live weight, dressing percent, fatness, carcass length, muscling, USDA grade and percent muscle.
Live Weight — Market hogs do not vary in live weight as much as beef cattle and can be subjectively estimated with more accuracy. The normal range is 190-270 pounds with an average of 245.
Dressing Percent — Dressing percent is highest of the three meat animal species. Due to the fact that pigs are only monogastrics. Dressing percent of market hogs with adequate condition should grade choice. The normal range is 68-77 percent with an average of 72.
Fat Depth — Last rib fat depth is measured at the last rib and is the primary factor in determining carcass grade. The tenth rib fat is measured between the 10th and 11th and is also used in calculating percent muscle.
Muscling — The degree of muscling of a hog is considered when grading market hogs and pork carcasses. Three degrees of pork carcass muscling are recognized in the pork grading standards.
Muscle Score #1 – Thin (Inferior)
Muscle Score #2 – Average
Muscle Score #3 – Thick (Superior)
Loin eye area is also another estimate of carcass muscle and is used in the percent muscle equation. It is measured between the 10th and 11th ribs on pork carcasses ad is highly correlated to carcass muscle. The normal range is 3.5-7 sq. inches with an average of 4.8.
USDA Grade — USDA grade is determined based on quality indicating characteristics of the lean and expected yield of the four lean cuts (ham, loin, picnic shoulder and Boston butt). The following equation is used to estimate the grade of barrow or gilt carcasses. USDA grade=(4 x Last Rib Backfat thickness, in.)–1 x muscle score
The muscle scores in this equation are: thin=1, average=2, and thick=3. Exceptions to this equations are that carcasses with thin muscling cannot grade U.S. No. 1 regardless of last rib fat depth (LRFD) and carcasses with 1.75 inches or more of LRFD cannot be graded as U.S. No. 3 regardless of muscling.
Percent Muscle — A more accurate and precise method of assessing differences in carcass yield of lean red meat. The factors used to predict percent muscle include hot carcass weight (HCW), loin eye area (LEA), and tenth rib fat depth (10RFD). The following is an equation used to estimate pounds of muscle containing five percent fat:
7.231 + (.437 x HCW) + (3.877 x LEA) – (18.746 x 10RFD)=Pounds of muscle containing five percent fat
Percent muscle can then be calculated as follows:
(Pounds of muscle/Hot carcass weight) x 100