EFFECTS OF DAYS FED, CARCASS GRADE TRAITS, AND SUBCUTANEOUS FAT REMOVAL ON POSTMORTEM MUSCLE CHARACTERISTICS AND BEEF PALATABILITY

Angus x Hereford steers (n = 48) similar in frame size and in muscle thickness were allotted to eight groups (n = 6) of similar mean live weight for serial slaughter at 28-d intervals (0 to 196 d). Except for d-0 steers, which served as grass-fed controls, all steers were fed a high-concentrate diet during the finishing period. Upon slaughter, one side of each carcass was trimmed of subcutaneous fat in the wholesale rib region. Postmortem longissimus muscle (LM) temperature was monitored for each side during the 24-h chilling period. After quality and yield grade data were collected, rib steaks were removed and aged (7 d) and sensory traits of the steaks were evaluated. Most carcass grade traits increased linearly (P < .01) with days on feed, whereas most sensory panel variables and marbling increased curvilinearly (P < .05). Generally, after 56 d on feed, carcasses chilled at slower rates (P < .05) with increased days fed. Taste panel tenderness, amount of perceived connective tissue, and shear force values peaked at 112 d and were slightly less desirable for cattle fed longer than 112 d (quadratic term, P < .01). Postmortem muscle temperature at 2.5 h was the chilling time most highly correlated with tenderness values among untrimmed sides. Correlations for shear force with 2.5-h LM temperature, marbling score, days fed, fat thickness, and carcass weight were -.63, -.61, -.56, -.55, and -.53, respectively. Sides trimmed of s.c. fat over the wholesale rib chilled more rapidly (P < .05) and had lower 2.5-h LM temperatures (P < .05) and lower (P < .05) sensory tenderness ratings than untrimmed sides. However, trimming of the s.c. fat did not (P > .05) affect shear force values. Path coefficient analysis revealed that LM temperature at 2.5 h could account for much (P < .05) of the variation in shear force values through both direct (r = -.50) and indirect (r = -.63) paths.