251 Evaluation of Condensed Algal Residue Solubles as an Ingredient in Cattle Finishing Diets

Algae oil production for Omega-3 fatty acid supplementation yields a byproduct called Condensed Algal Residue Solubles (CARS; 25.4% DM, 19.3% CP, 8.3% Fat, 9.96% Na on DM basis), de-oiled algae cells with residual fermentation substrates. This study evaluated the use of CARS in feedlot finishing diets. Crossbreed steers, (n=480) were blocked and stratified by initial body weight (BW) into 4 blocks, and assigned randomly to treatments. Treatments were designed as a 2 x 3 factorial with 3 inclusions of CARS (0, 2.5, 5% of diet DM) and 2 different base diets representing Northern and Southern Great Plains diets. The Southern diets contained steam flaked corn and dry distillers grains while the Northern diets had dry rolled and high moisture corn with wet distillers grains. CARS replaced corn in both diets. All blocks were harvested after 148 days on feed. Performance data were analyzed as a randomized block design with CARS inclusion, base diet, and interactions as fixed effects, BW block as a random effect and pen (n=48) as the experimental unit. Orthogonal contrasts were used to test linear and quadratic effects of CARS inclusion. There were no significant interactions between CARS inclusion and diet type (P ≥ 0.49). Main effects of CARS indicated positive quadratic responses for carcass adjusted ADG, G:F, 12th rib back fat, yield grade (P < 0.01; increasing to 2.5% inclusion, decreasing at 5%) and hot carcass weight was both linear and quadratic (P ≤ 0.01 and P ≥ 0.06 respectively; 969, 977, 935 as CARS increased). Linear decrease in DMI, final adjusted BW and ribeye area (P ≤ 0.01) as CARS increased. Cattle fed the Southern diets had greater ADG and G:F compared to Northern diets (P < 0.01). Including 2.5% CARS in the diet improved feed efficiency in both Northern and Southern based feedlot diets.