Animal Feed Science and Technology 141 (2008) 339–355 Available online at www.sciencedirect.com In vitro biohydrogenation of four dietary fats M. Carriquiry a , W.J. Weber a , L.H. Baumgard b , B.A. Crooker a,∗ a Department of Animal Science, University of Minnesota, St. Paul, MN 55108-6118, USA b Department of Animal Sciences, University of Arizona, Tucson, AZ 85721-0038, USA Received 28 November 2006; received in revised form 9 May 2007; accepted 19 June 2007 Abstract This study was designed to determine in vitro rates of biohydrogenation of dietary unsaturated fatty acids by a mixed population of rumen microbes. The four dietary fats [Alifet High-Energy ® (AHE), Alifet-Repro ® (AR), Megalac ® (MG), and Energy Booster ® (EB)] differ in method of preparation, fatty acid composition, or both of these factors. Dietary fats (20 mg) were incubated with 4 mL strained rumen fluid diluted with 16 mL of medium, 0.8 mL of reducing solution buffer, and 200 mg of a synthetic diet (370 g cellulose, 370 g starch, and 160 g casein per kg DM) at 37 ◦ C. Total contents were collected after 0, 6, 12, 24, or 36 h and change in fatty acid content determined. Disappearance of oleic acid was minimal (0.05–0.20) in AR and MG but moderate (about 0.60) in AHE and EB after 36 h of incubation. Rate of biohydrogenation of linoleic and linolenic acids from AR were similar (0.025 ± 0.009 h -1 ) and 0.65 of these fatty acids remained intact after 36 h. Rate of biohydrogenation of linoleic acid was four times greater than for oleic acid (0.040 ± 0.013 h -1 versus 0.009 ± 0.002 h -1 ) in MG. Thus, 0.65 of the linoleic acid but only 0.20 of the oleic acid had disappeared from MG after 36 h. Trans-11 and trans-12 were the predominant trans-isomers in AHE and AR cultures whereas trans-9 and trans-10 were the predominant trans-isomers in EB and MG cultures. None of the dietary fats contained conjugated linoleic acid (CLA) but CLA was present in the incubation inoculum. The amount of CLA decreased with time but this was not affected by source of dietary fat. Most (0.90–0.95) of the long-chain fatty acids eicosapentaenoic (EPA) and docosahexaenoic (DHA) in AR remained after 36 h of incubation. Results demonstrate that biohydrogenation varied among fatty acids and Abbreviations: AHE, Alifet-High Energy ® ; AR, Alifet-Repro ® ; CLA, conjugated linoleic acid; DHA, docosa- hexaenoic acid; DM, dry matter; EB, Energy Booster ® ; EPA, eicosapentaenoic acid; MG, Megalac ® ∗ Corresponding author at: 205 Haecker Hall, Department of Animal Science, University of Minnesota, 1364 Eckles Avenue, St. Paul, MN 55108-6118, USA. Tel.: +1 612 625 3185; fax: +1 612 626 1289. E-mail address: crook001@umn.edu (B.A. Crooker). 0377-8401/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2007.06.028