Supplemental algal-meal alters the ruminal trans-18:1 fatty acid and CLA composition in cattle

¹ Food Research Program, Agriculture and Agri-Food Canada, Guelph, ON, Canada N1G 5C9
² Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada N1G 2W

^* To whom correspondence should be addressed. E-mail: mamum76{at}hotmail.com.

	Abstract

The effects of dietary algal supplementation, a source of docosahexaenoic acid (DHA), on the fatty acid profile of rumen lipids in cattle was evaluated, with special emphasis on CLA and trans fatty acids produced by rumen microbes. A diet based on corn silage was fed with supplements containing: 1) no algal-meal and fed at 2.1 kg of DM/d (control), 2) algal-meal and fed at 1.1 kg of DM/d (low algal-meal), 3) algal-meal and fed at 2.1 kg of DM/d (medium algal-meal), and 4) algal-meal and fed at 4.2 kg of DM/d (high algal-meal). A modified lipid extraction procedure was developed to analyze the lipid changes in rumen fluid. The percentage of stearic acid (18:0) was decreased by algal-meal supplementation (P < 0.001) compared to control and was linearly dependent on the level of algal-meal supplementation (P = 0.005). Total trans-18:1 in rumen fluid of cattle fed the control diet was 19% of total fatty acids. Addition of algal-meal increased (P < 0.001) total trans-18:1 up to 43%, mostly due to 18:1 trans-10 that increased (P = 0.002) up to 29.5% of total rumen fatty acids. This increase in 18:1 trans-10 seems to suggest a change in the rumen microbial population. Vaccenic acid (18:1 trans-11) increased quadratically (P = 0.005) with increasing level of algal-meal supplementation in the diets. The total CLA content was low in the control (<0.9%) and increased with dietary algal-meal addition although not significantly; the highest level was 1.5% with the medium-level algal-meal diet. The increase of rumenic acid (cis-9, trans-11 CLA) was quadratic (P = 0.05) with algal-meal supplementation, whereas trans-10, cis-12 CLA increased linearly wtih increased level of algal-meal from 0.08 to 0.13% (P = 0.03). The ratio of trans-11 (cis-9, trans-11 CLA + 18:1 trans-11) to trans-10 (trans-10, cis-12 CLA + 18:1 trans-10) decreased from 2.45 to 0.77, 0.87, and 0.21, for the control, low algal-meal, medium algal-meal, and high algal-meal diets, respectively. The content of DHA in rumen fluid increased (P = 0.002) from 0.3 to 1.4% of total fatty acids with increasing level of algal meal supplementation in diets. Our results suggest that algal-meal inhibits the reduction of trans-18:1 to 18:0 giving rise to the high trans-18:1 content. In conclusion, algal-meal could be used to increase the concentration in rumen contents of trans-18:1 isomers that serve as precursors for CLA biosynthesis in the tissues of ruminants.

Key Words: Algal-meal, CLA, docosahexaenoic acid, rumen fluid, vaccenic acid