Can Extruded Soybeans Provide Additional Fat and Protein to Cattle Diets?

Abstract Extruded soybean inclusion could be a strategy to increase dietary fat and enhance protein quality in diets fed to feedlot cattle. Angus-influenced steers (n = 240 steers; ISBW = 409 ± 23.5kg) were fed one of three diets for 150 days. The study was conducted as a randomized complete block design (RCBD; blocked by batch fraction) and steers were allotted to 24 pens (10 steers/ pen; 8 pens/ treatment). Dietary treatments were based on protein and fat source, as follows: 1) a diet containing low-fat modified distillers grains with solubles (MDGS, diet ether extract EE = 3.7% DM basis), 2) a diet containing MDGS and corn oil (MDGS+OIL, diet EE = 5.8% DM basis), and 3) a diet containing extruded soybeans to provide the same fat content as the MDGS+OIL treatment (ESB, diet EE = 5.9% DM basis). Diets were based upon dry-rolled corn, supplemental protein, grass hay, corn silage and a suspended supplement. The average inclusion of low-fat modified distillers grains with solubles was 19.79% for MDGS and 19.80% for MDGS+OIL, the average inclusion of extruded soybeans in ESB was 16.28% (DM basis). Steers were fed once daily; bunks were managed using a slick-bunk system. Body weights were recorded on days -1, 1, 36, 64, 99 and 150. Steers were implanted with 200 mg trenbolone acetate and 20 mg estradiol-17β (Revalor-200, Merck Animal Health, DeSoto, KS) on day 36. Steers received 36 mg daily of lubabegron fumarate (Elanco, Indianapolis, IN) from day 100 to day 147. On day 150 the steers were transported to a commercial abattoir (Tyson Fresh Meats, Dakota City NE) and harvested 24 h later to analyze carcass characteristics and liver scores. Pen served as the experimental unit for all data analyses. Distribution of USDA Yield and Quality grade and liver scores were analyzed as multinomial proportions. Statistical models included the fixed effect of dietary treatment with block considered a random effect. Steers fed ESB had greater carcass-adjusted final body weight (2.9 and 1.7%), ADG (6.4 and 3.6%), and G:F (4.0 and 4.0%) than steers fed the MDGS and MDGS+OIL diets (P = 0.01).Feeding ESB increased HCW (P = 0.01) by 2.8% and 1.7% compared to MDGS and MDGS+OIL diets, respectively. No differences were observed for dressing percentage, fat thickness or REA between treatments (P ≥ 0.35). Steers fed ESB tended to have 6.5 and 20.3% fewer edible livers (P = 0.09) compared to steers fed MDGS and MDGS+OIL, respectively. These results indicate feeding ESB can improve growth performance and HCW but may decrease edible livers. Adding corn oil to the MDGS-based diet was not sufficient to match the growth performance of ESB-fed steers.