Post-extraction algal residue as a protein supplement for beef steers consuming forage: Palatability and nutrient utilization

•Post extraction algal residue stimulates forage utilization in beef cattle.•Palatability and mineral content limits inclusion of post extraction algal residue.•Blending post extraction algal residue with other ingredients mitigates constraints. Post-extraction algal residue (PEAR), the co-product of algal biofuel production, has potential to be incorporated as an ingredient in ruminant diets. Market value of PEAR will be driven by its ability to compete with commonly fed protein sources, such as cottonseed meal (CSM) and dried distillers’ grains (DDG). Two experiments were conducted to evaluate the potential for PEAR to be incorporated in existing protein supplementation strategies of the beef industry. In Experiment 1, 12 steers were used in a 12 × 12 Latin square experiment consisting of 12, 4-d periods to evaluate the palatability of PEAR at divergent inclusion levels and with differing carriers (DDG; CSM; liquid supplement, LS) as a supplement to cattle consuming a basal diet of Bermudagrass hay. Each period included 3-d where steers were fed a test supplement followed by a 1-d washout where steers were fed DDG. Blends were formulated with carrier ingredients (CSM, DDG, or liquid supplement, LS) at varying levels of PEAR inclusion; PEAR and carrier ingredients were also offered as stand-alone supplements. Completion rate and consumption rate (g supplement consumed/min) were recorded daily. In Experiment 2, six steers were used in concurrent 3 × 3 Latin Square experiments to determine the effect of PEAR on nutrient utilization and mineral intake in steers consuming low-quality forage. Treatments included no supplemental protein (CON) and isonitrogenous levels of PEAR or CSM (100 mg N/kg BW). In Experiment 1, completion rate was ≥90 % for DDG- and CSM-based blends, which was greater (P < 0.05) than when PEAR was offered alone (56 %). Consumption rate of 100 % PEAR was similar (P ≥ 0.05) to that of most CSM-based supplements, approximately 148–154 g supplement consumed/min. In Experiment 2, provision of isonitrogenous levels of PEAR and CSM stimulated (P ≤ 0.05) total digestible OM intake to a similar extent (P = 0.98), from 2.35 (CON) to 2.82 kg/d (PEAR and CSM). OM and NDF digestion were similar for all treatments (P ≥ 0.23), ranging from 56 to 59% (OM) and 49–54 % (NDF). Supplemented steers retained and absorbed more N (P ≤ 0.02) than CON. Supplementation of PEAR (100 mg N/kg BW) to steers consuming low-quality forage resulted in a Ca:P ratio of 8:1,