Abstract
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.
Highlights
Grass-fed beef has been marketed in different countries as a leaner product, with an altered fatty acid composition
One of the major objectives of the present study was to evaluate the effect of different type of energy supplementation on longissimus muscle fatty acid composition as compared to non-supplemented grazing steers or concentrate-finished steers
An overview of general dietary treatment effects on longissimus muscle fatty acid profile can be observed on the scoring plot (Fig. 1) where the steers sorted into three main groups
Summary
Grass-fed beef has been marketed in different countries as a leaner product, with an altered fatty acid composition. Grass-fed beef has lower proportions of the highly atherogenic myristic and palmitic acids than concentrate-fed beef and greater of the anti-atherogenic and anti-carcinogenic cis-9, trans-11 conjugated linolenic acid (CLA) and of its precursor, the trans-11 vaccenic acid (TVA; Daley et al, 2010). Increasing corn grain supplementation to grazing steers changes the fatty acid profile toward that observed in feedlot-finished cattle (Garcia et al, 2008), whereas increasing corn oil supplementation to grazing steers has shown to reduce palmitic acid and increase CLA and TVA proportions (Pavan and Duckett, 2007). We observed that when equal amounts of metabolizable energy (ME) are supplemented to grazing steers with corn grain or corn oil plus soybean hulls, similar improvement of animal performance could be obtained (Pavan and Duckett, 2008). The type of energy supplemented had a differential effect on fatty acid metabolism of
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