Fish oil (FO) alters ruminal biohydrogenation causing trans fatty acid (FA) intermediates to accumulate, but the effects of 18-carbon polyunsaturated FA supply on ruminal long-chain FA metabolism and microbial communities in cattle fed FO are not well established. Four cows fitted with rumen cannula were used in a 4 × 4 Latin square with 21-d experimental periods to evaluate the effects of FO alone or in combination with plant oils high in 18:2n-6 or 18:3n-3 on rumen microbial ecology and flow of FA at the omasum. Treatments comprised a basal grass silage-based diet containing no additional oil (control) or supplements of FO (200 g/d) or FO (200 g/d) plus 500 g/d of sunflower oil (SFO) or linseed oil (LFO). Flow of FA was determined using the omasal sampling technique. The relative abundance of key biohydrogenating bacteria was assessed by quantitative PCR on 16S rRNA genes in omasal digesta. Fish oil-supplemented treatments increased the amounts of trans-18:1, trans-18:2, and 20- to 22-carbon polyunsaturated FA escaping the rumen. Relative to the control, oil supplements had no effect on the amount of 18:0 leaving the rumen, but LFO decreased the flow of 18:0 at the omasum compared with SFO. Both SFO and LFO increased trans-18:1 relative to FO, whereas LFO resulted in the highest trans-18:2 and 20- to 22-carbon FA flow. Supplements of FO plus plant oils shifted biohydrogenation toward trans-10 18:1 formation. Compared with FO alone, the ruminal metabolism of 22:6n-3 in the rumen of lactating cows is more extensive on diets containing higher amounts of 18-carbon polyunsaturated FA. However, the biohydrogenation of 22:5n-3 was less extensive in LFO than SFO, but showed no difference between FO and diets containing plant oils. Ruminal outflow of 20:5n-3 was not altered when plant oils were added to FO. Alterations in the amount of intermediates at the omasum or ruminal biohydrogenation pathways were not accompanied by major changes in analyzed bacterial populations. In conclusion, dietary supplements of FO alone or in combination with plant oils increase the amount of biohydrogenation intermediates containing 1 or more trans double bonds escaping the rumen, which may have implications for host metabolism and the nutritional quality of ruminant foods.
Bibliographical noteThe authors dedicate this article to the memory of late Kevin J. Shingfield with gratitude for his inspiration, guidance, and commitment to this work and above all for his warm and everlasting friendship. The authors appreciate the contribution of staff at the Animal Nutrition Section Metabolism Unit of MTT Agrifood Research Finland [Natural Resources Institute (LUKE) since 2015; Jokioinen, Finland] for the care of experimental animals and assistance during sample collection. Valued contributions of Minna Aalto (Luke, Jokioinen, Finland) and Nest McKain (University of Aberdeen, Aberdeen, UK) for help with lipid and microbial ecology analyses, respectively, are very much appreciated. The authors gratefully acknowledge members of the LUKE Feed Laboratory for assistance with sample analyses. Provision of ultra-refined herring and mackerel oil by Pronova Biocare AS (Aalesund, Norway) and sunflower oil by Raisioagro Ltd. (Raisio, Finland) are gratefully acknowledged. This work was supported by BioCLA, an European Union 5th Framework Program Project (QLK1-2002-023621, European Commission, Brussels, Belgium) Production of CLA Enriched Products by Natural Means. Collaboration between research partners was funded by LIPGENE (www.lipgene.tcd.ie), an EU Sixth Framework Programme Integrated Project (FOOD-CT-2003–505944, European Commission, Brussels, Belgium).
- plant oil
- polyunsaturated fatty acid