Effects of Dietary Fat Source and Modified Distillers Grains on Beef Quality

This research was conducted to evaluate the effects of feeding different fat sources with modified distillers grains plus solubles (MDGS) on beef tenderness, discoloration, lipid oxidation, and fatty acid profile. Steers (n=256) were fed for 134 d on either a corn control, 40% full-fat modified distillers grains plus solubles (MDGS), 40% de-oiled MDGS, or 38% de-oiled MDGS plus 2% corn oil diet. Cattle were grouped 8 per pen for a total of 32 pens. Twenty four low Choice carcasses (3 head/pen) were randomly selected within each treatment (n=96) and strip loins (left and rights sides) were collected and aged for 2, 9, 16, or 23 d. Steaks were fabricated at each aging period and placed under retail display conditions for 0, 4, or 7 d. Tenderness (slice shear force and Warner-Bratzler shear force), discoloration, lipid oxidation, and fatty acid composition were determined. No differences among treatments were observed for slice shear force (P=0.7851) and Warner-Bratzler shear force (P=0.4818). A treatment-by-retail display interaction (P =0.0004) was found for discoloration. Strip loins from steers fed de-oiled MDGS had greater discoloration rates in comparison to beef from the corn fed cattle at 7 d retail display (65.16%, and 49.82%, respectively). Samples from the full-fat and de-oiled MDGS plus oil groups were not different in discoloration from corn or de-oiled MDGS fed cattle (58.08% or 58.64%, respectively). There was a treatment-by-retail display interaction for lipid oxidation (P =0.0045). Strip loins from steers fed de-oiled MDGS and de-oiled MDGS plus oil had numerically, but not statically (P > 0.05), greater TBARS values in comparison to corn as retail display progressed. Beef from the corn control cattle had the least amount of C18:2 (P=0.0007) in comparison to all other dietary treatments (6.16% vs. 7.62% for the de-oiled MDGS plus oil, 8.02% for the full-fat MDGS, and 8.20% for the de-oiled MDGS groups). Similarly, beef from corn cattle had the least amount (P=0.0231) of polyunsaturated fatty acids (PUFA, 8.86%) while beef from cattle fed de-oiled MDGS had the greatest amount of PUFA (10.87%). Samples from the full-fat MDGS and de-oiled MDGS plus oil groups were not different from corn or de-oiled MDGS fed cattle (10.66% or 9.95%, respectively).These results suggest that feeding de-oiled MDGS to cattle reduces color and lipid stability and increases PUFA and C18:2 content of the meat. Addition of corn oil to the de-oiled MDGS had no effect on the results.