Variation in and effects of prefabrication fat trimming on yields and prediction equation accuracies of retail product and fat trim

Abstract

Carcass data from one side of 1,149 steers born from 1986 to 1990 were analyzed to develop means for carcass traits and retail product percentage by yield grades. Carcasses from 610 of these steers born from 1988 to 1990 were fabricated to two fat trim levels (.30 and .00 in.), with subcutaneous fat and intermuscular (internal) fat weighed separately. Subcutaneous fat from the primal round, loin, rib, chuck, brisket, and flank in excess of .30 in. plus the kidney knob were considered to constitute an industry ‘hot-fat trim equivalent’ (HFTE). Quadratic regression curves were plotted for percent retail product (RP) and percent fat trim (FT) vs. USDA yield grade. In addition, prediction equations were developed for weights and percentages of RP and FT that could be used in plants that do hot-fat trimming and quality grading of carcasses. Percentage of RP, trimmed to either .30 or .00 in. of fat, decreased an average of 4% for each full yield grade increase. Trimming to .00 in. of fat instead of .30 in. reduced RP about 5.5%. The average percentage of HFTE for a yield grade 3.0 carcass was 8.4%. The range in percentage of RP at both trim levels was reduced by trimming fat to an HFTE basis , but considerable range still existed. The range in percentage of internal (seam) fat across yield grades was greater than the range in percentage of HFTE. An equation to predict percentage RP in HFTE carcasses using percentage of hot fat trim, carcass weight, ribeye area, and marbling score had an R2 of .75, which was considerably higher than that for an equation using USDA yield grade traits from untrimmed carcasses (R2=.54). The high accuracy of our prediction equation suggests that the industry could use it to accurately predict closely trimmed RP percentage of hot-fat trimmed carcasses.