Relationships among measures of growth performance and efficiency with carcass traits, visceral organ mass, and pancreatic digestive enzymes in feedlot cattle.

Ninety-three crossbred steer calves (BW+/-SD=385+/-50 kg) were used (n=48 steers in yr 1, n=45 steers in yr 2) to examine the relationship among carcass traits, lean, bone, and fat proportions, visceral tissue weights, and pancreatic digestive enzyme activity with DMI, ADG, G:F, and residual feed intake. Calves were progeny from crossbred dams predominantly of Angus and Simmental breeding and were sired by Angus, Simmental, crossbred (predominantly of Angus and Simmental breeding), Charolais, or Piedmontese bulls. Steers were fed a high-moisture corn-based diet for an average of 112 d. Partial correlation analysis accounting for year, pen within year, week of slaughter within year, and sire breed was conducted. Gain:feed was negatively correlated (P <or= 0.04) with backfat thickness (r= -0.38), marbling score (r= -0.32), and trim and kidney fat weight proportion (g/kg of BW; r= -0.42). Residual feed intake (P=0.008; g/kg of BW; r=0.34) and backfat-corrected residual feed intake (P=0.005; r=0.29) were positively correlated with trim and kidney fat weight proportion. Gain:feed was negatively correlated (P<0.001) with total fat weight proportion (g/kg of rib; r= -0.45) and positively correlated (P <or= 0.03) with lean weight proportion (g/kg of rib; r=0.30) and bone weight proportion (g/kg of rib; r=0.28). Gain:feed was negatively correlated (P <or= 0.01) with subcutaneous fat weight proportion (g/kg of rib; r= -0.32) and intramuscular fat weight proportion (g/ kg of rib; r=0.37). Gain:feed was negatively correlated (P<0.001) with total visceral weight proportion (g/kg of BW; r= -0.44) and visceral fat weight proportion (g/kg of BW; r= -0.41) but was positively correlated (P=0.02) with spleen weight proportion (g/kg of BW; r=0.30). There were no significant correlations (P>0.10) between performance measures and the pancreatic proportional content of alpha-amylase and trypsin activity (units/kg of BW). These data indicate that carcass fatness traits and changes in the proportional weight of total viscera may be negatively associated with G:F and that visceral fat weight proportion and trim and kidney fat weight proportion may be important factors influencing this relationship.