New approaches and development and improvement of methodologies for the assessment of fatty acid nutrition in ruminants

The absorbed FA profile has significant impacts on animal production and physiology especially with our current appreciation of the function of bioactive fatty acids (FA). In the ruminant, the absorbed fatty acid profile is dependent on both feed composition and ruminal biohydrogenation. Microbial biohydrogenation is a multi-step process and the rates and control points are not well understood. Biohydrogenation is dependent on the amount and profile of FA fed, rumen availability of FA, and the rumen microbial population. Many dietary and environmental factors also modify ruminal biohydrogenation creating numerous interactions. The importance of biohydrogenation has been highlighted in dairy production with the development of the biohydrogenation theory of milk fat depression, where specific biohydrogenation intermediates pass from the rumen and impact mammary capacity for lipid synthesis. Ruminal biohydrogenation also greatly limits our ability to improve the omega-3 FA status of the cow, which may benefit reproductive efficiency and immune function, and increase the unsaturated and omega-3 FA concentration of meat and milk. Advances in fatty acid methodology have aided our understanding, but key technical issues must be considered to reduce bias. Investigations using in vitro, in situ, and in vivo approaches are reviewed and mechanistic models are proposed. Care should be taken in selection of analytical methods and identification of FA in chromatography. Future hypothesis driven research is expected to provide a more clear understanding of ruminal biohydrogenation and allow prediction of duodenal flow by mathematical models.