Effect of algae on rumen biohydrogenation of polyunsaturated fatty acids

The increased consumption of animal fat has been associated with a higher incidence of chronic diseases such as cardiovascular diseases, obesity and diabetes due to the specific fatty acid composition of animal products. Nutritional recommendation in terms of dietary fat emphasize on an increased consumption of polyunsaturated fatty acids (PUFA) and on a decrease in dietary saturated fatty acids (SFA). Ruminant milk has often been criticized for its high SFA content and low n-3 fatty acids content, resulting from the de novo synthesis of SFA in the mammary gland and the active rumen biohydrogenation of dietary PUFA. On the other hand, the rumen microbial community produces fatty acids that are relatively unique to ruminant products and that were suggested to possess health-promoting properties. Hence, to improve the fatty acid composition of milk and to increase the human consumption of CLA and n-3 fatty acids, research on the potential to steer the rumen fatty acid metabolism is necessary. The main objectives of this PhD research were 1) to assess the effect of algae supply on the rumen lipid metabolism as well as rumen fermentation in vitro, 2) to further validate dietary algae supply in vivo in terms of animal performances and milk fatty acid profiles and 3) to characterize microorganisms involved in the rumen biohydrogenation process. The results of this PhD thesis indicate that dietary algae supply might represent an effective means to modify the rumen biohydrogenation process and to optimize the milk fatty acid profile. Rumen ciliates seem not involved in the rumen lipid metabolism while a significant role in rumen biohydrogenation might be attributed to yet unknown and uncultured bacterial species within the genera Butyrivibrio and Pseudobutyrivibrio