title: Effect of increasing amounts of postextraction algal residue on straw utilization in steers.
abstract: Algal biomass has been identified as a third-generation biofuel. Significant quantities of the coproduct postextraction algal residue (PEAR) remain after lipid extraction. After extraction, PEAR is concentrated in protein (17.9% CP on a DM basis and 32.5% CP on an ash-free basis), suggesting it may be an alternative to cottonseed meal (CSM) as a protein supplement. Our objectives were to determine the optimal level of PEAR supplementation to steers consuming straw and to compare the effects of PEAR supplementation on straw utilization and N metabolism with an isonitrogenous level of CSM. Five steers (198.2 ± 6.1 kg of BW), in a 5 × 5 Latin square, had ad libitum access to oat straw (80% NDF and 4.5% CP on a DM basis). Treatments were infused ruminally once daily and included no supplemental protein (CON); PEAR at 50, 100, and 150 mg N/kg BW; and CSM at 100 mg N/kg BW. Provision of PEAR increased total digestible OM intake (TDOMI) quadratically (P = 0.01) from 0.9 (CON) to 1.6 kg/d (100 mg N/kg BW of PEAR). Organic matter digestibility (OMD) increased quadratically (P < 0.01) with supplementation and was maximized (55% OMD) at 50 mg N/kg BW of PEAR. At isonitrogenous levels of PEAR and CSM, TDOMI was similar (P = 0.13) as was OMD (P = 0.50). Negative N balance was observed for all treatments except PEAR provided at 100 or 150 mg of N/kg BW. Nitrogen balance was quadratic (P < 0.01) with the greatest retention (1.84 g N/d) occurring at 100 mg N/kg BW of PEAR. There were no differences (P ≥ 0.22) between isonitrogenous PEAR and CSM supplementation in measurements of ruminal ammonia or VFA concentrations. Straw utilization was maximized when PEAR was provided at 100 mg N/kg BW. Our observations suggest cattle provided PEAR utilize straw in a manner similar to those supplemented CSM, indicating PEAR has potential to substitute for CSM as a protein supplement in forage-based operations.
authors.affiliation: Texas A&M University, College Station 77843.
authors.forename: M L
authors.initials: ML
authors.lastname: Drewery
authors.affiliation: Texas A&M University, College Station 77843.
authors.forename: J E
authors.initials: JE
authors.lastname: Sawyer
authors.affiliation: Texas A&M AgriLife Research, Vernon 76384.
authors.forename: W E
authors.initials: WE
authors.lastname: Pinchak
authors.affiliation: Texas A&M University, College Station 77843 tryon@tamu.edu.
authors.forename: T A
authors.initials: TA
authors.lastname: Wickersham
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D018554:Avena / Q000737:chemistry*; D002417:Cattle; D002708:Chlorella / Q000737:chemistry*; D019587:Dietary Supplements / Q000032:analysis*; D004063:Digestion / Q000502:physiology*; D004435:Eating / Q000502:physiology; D008297:Male
chemical_list: D000641:Ammonia
keywords: cattle; postextraction algal residue; protein; straw; supplementation