| Summary: | Twenty-eight Angus (289 ± 3.8 kg) steers were used to evaluate the effect of isocaloric supplementation of 2 different energy sources to steers grazing tall fescue pastures for 197 d on longissimus muscle fatty acid profile, shear force, tenderness and color. Steers were supplemented with either corn grain (PC) or soybean hulls plus corn oil (PO). A negative control, pasture only (PA), and positive control, high-concentrate control diets (CONC) were also included in the study. Total trans-11 vaccenic acid (TVA) and cis-9, trans-11 CLA content per serving were similar with PA, PC and CONC and greatest with PO (P < 0.001). Muscle total fatty acids, myristic and palmitic contents per serving were similar with PC, PO, and PA and greatest with CONC (P < 0.001). Muscle PUFA n-6:n-3 ratio was greater with PC than with PA and lower with PC than with CONC, but it was greatest with PO (P < 0.001). Shear force was lower (P = 0.046) with CONC than with PA and PC; beef from PO did not differ from any of the other treatments. Sensory panel scores for overall tenderness (P < 0.001) were greatest with CONC, greater with PO than with PC, and similar with PA than with PO and PC. Muscle lightness was similar for PO and PC, greater with PO and PC than with PA and lower with PO and PC than with CONC (P < 0.001). Treatment by time postmortem interaction was significant for muscle temperature (P < 0.001), but not for muscle pH (P = 0.79). Temperature decline was fastest with PA and slowest with CONC. Postmortem muscle pH was greater with PA, PC, and PO than with CONC (P = 0.011). Overall, fatty acid profile with PC was closer to the fatty acid profile with PA than that with PO or CONC. Finishing systems altered fat deposition, which impacted chilling rate, muscle color and palatability.
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