Effects of varying corn or soybean co-product inclusion in finishing diets of feedlot heifers on carcass characteristics and fresh meat quality

Abstract Text: The impact of using corn or soybean co-product in high or low corn grain finishing diets of feedlot heifers was evaluated. Forty-four purebred Limousin heifers were used in a randomized design with four treatments: 65% corn grain (CG) diets with either 20% modified distillers grains with solubles (MDGS; HI+MDGS) or a combination of glycerin and high fiber, high protein soybean co-product (SOY; HI+SOY) or 25% CG diets with 60% MDGS (LO+MDGS) or with 40% MDGS and 20% SOY (LO+MDGS+SOY).  All heifers received melengestrol actetate and Rumensin. Experimental unit was individual heifer, as all animals were fed individually using a Calan gate system.   Response variables evaluated included carcass characteristics and fresh meat quality characteristics.  Heifers were fed finishing diets for 129 d and were humanely harvested at a commercial facility. Hot carcass weight (HCW); 12^th rib back fat (BF); rib eye area (REA); percent kidney, pelvic, and heart fat (KPH); and marbling score were collected 48 h post mortem by trained plant personnel. Carcasses were fabricated by plant personnel and strip steaks were collected for drip loss, Warner-Bratzler shear force, and retail shelf life evaluation.  Six readings per strip steak were recorded for Warner-Bratzler shear force values and eight replicates were recorded for 7-day retail shelf life on strip steaks.  There was no treatment effect for HCW (P = 0.37), BF (P = 0.10), REA (P = 0.63), KPH (P = 0.67), or marbling score (P = 0.18).  Drip loss did not differ among treatments (P = 0.85).  Treatment affected Warner-Bratzler shear force (P = 0.03) of strip steaks. Warner-Bratzler shear force of strip steaks from HI+SOY (3.17 kg) and LO+MDGS+SOY (3.79 kg) were different (P = 0.02).  Treatment did not affect subjective scores for lean color (P = 1.00), surface discoloration (P = 0.19), and overall appearance (P = 0.52) of strip steaks. Results indicate feeding high levels of corn or soy co-product in feedlot heifer diets does not have an effect on carcass characteristics, drip loss, or subjective retail shelf life evaluation; however, combining all co-products in a low grain inclusion diet impacted Warner-Bratzler shear force.  

Keywords: Modified Distillers Grains, Beef, Fresh Meat Quality