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Yield Grade
Yield grade is an indication of retail product yield from the carcass which is expressed in whole numbers from one to five or in tenths of a grade. Expressing yield grade in tenths of a grade is desirable in making comparisons, although in retail marketing, decimals are dropped. Yield grades are calculated by the following formula:
Yield Grade = 2.50 + (2.5 × Adj. fat thickness, in.)
+ (0.2 × Kidney, pelvic, and heart fat, %)
+ (0.0038 × Hot carcass wt., lb.)
– (0.32 × Ribeye area, sq. in.)
Adjusted fat thickness is an estimate of external fat, which is the most important factor in determining retail yield. It is measured at the 12th rib, perpendicular to the outside fat at a point three-fourths of the length of the ribeye muscle from the backbone. This measurement often is adjusted to reflect unusual fat distribution of the carcass. As external fat increases, the percentage of retail product decreases.
Estimated percentage of kidney, pelvic, and heart fat (KPH) estimates fat in the kidney knob, pelvic, and heart areas as a percentage of carcass weight. As KPH fat increases, the percentage of retail product from the carcass decreases.
Ribeye area is an indicator of muscling. The longissimus or ribeye muscle is measured at the 12th rib by using a grid or a ribeye tracing that is measured with a compensating polar planimeter or image-analysis system. As ribeye area increases, retail product yield increases.
Hot carcass weight is recorded as the carcass leaves the slaughter floor. Generally, as animals increase in weight, the percentage of retail product decreases because of increased fat deposition.
Total Percentage of Retail Product
Dikeman et al. (1998, J. Anim. Sci. 76:1604-1612) developed an equation that uses traits in the USDA Yield Grade system to predict percentage of total retail product trimmed to zero (0.0) in. of surface fat, as follows (predictive model R2 = 0.54):
% Total Retail Product = 65.59 – (9.93 × Adj. fat thickness, in.) – (1.29 × Kidney knob, %) + (1.23 × Ribeye area, sq. in.) – (0.013 × Hot carcass wt., lb.)
If cattle are slaughtered at a plant that uses hot fat trimming, the following equation by Apple et al. (1991, J. Anim. Sci. 69:4845-4857) can be used (predictive model R2 = 0.75):
% Total Retail Product = 78.95 – (0.005 × Hot carcass wt., lb.) – (1.56 × Hot fat trim, %) + (0.516 × Ribeye area, sq. in.) – (1.14 × Marbling score: 4.0 to 4.9 = slight, etc.)
