THE ILLINOIS SPRING BARROW SHOW: CARCASS TRENDS FROM 1968 TO 1989 AND USE OF CARCASS CHARACTERISTICS TO PREDICT DRESSING PERCENTAGE

The Illinois Spring Barrow Show, a large annual carcass show of performance-tested pigs, may provide an indication of phenotypic trends in the pork industry over time. Objectives of this study were 1) to investigate time trends in live and carcass weights (LWT, CWT), dressing percentage (DP), length (LEN), loin muscle area (LEA), backfat (BF), muscle color, firmness and marbling (C,F,M) scores, estimated fat-standardized lean yield (FSL), FSL/d of age (LDOA) and FSL/d on test (LDOT) and 2) to assess use of carcass characteristics to predict DP. Data on 5,983 barrows exhibited between 1968 and 1989 were analyzed. Linear regressions expressed as change/yr (1977 to 1989, all P < .001) were .56 kg (LWT), .53 kg (CWT), .11 % (DP), .50 mm (10th rib BF), −49 g (wt-adj. FSL), 2.0 g (wt-adj. LDOA, 1977 to 1983) and −2.2 g (wt-adj. LDOT, 1984 to 1989). There were only small changes in LEN, C, F and M. Between 1968 and 1976, LEA increased .42 cm2/yr, then decreased .23 cm2/yr until 1984, increased .34 cm2/yr to 1988 and fell 1.2 cm2 in 1989 (all P < .001). Models including year, breed and their interaction (YB), ± linear and quadratic regressions on LWT, CWT, 10th rib BF, LEA and LEN, were used to assess the amount of variability in DP that could be accounted for by these carcass measures. R2 values (model effects in parentheses) were .16 (YB ± LWT), .28 (YB + CWT ± BF ± LEA) and .31 (YB + CWT + LEN ± [BF + LEA]). In conclusion, performance tested carcass show barrows have become heavier and fatter over time. Lean growth rate has decreased over the past 5 yr. Tenth rib fat and loin muscle area had no value as predictors of dressing percentage. Dressing percentage was not useful as a predictor of lean growth rate or lean yield.