Acetate conversion to fatty acids in adipose tissue requires NADPH which, in ruminants, is generated mainly by the oxidation of glucose via the pentose phosphate pathway and from acetate via the isocitrate cycle. In ruminants negligible amounts of glucose are absorbed from the alimentary tract and glucose is synthesized from propionic acid and gluconeogenic amino acids in the liver. Silage diets are high in lipogenic precursors (acetate and butyrate) but characterized by low amounts of gluconeogenic precursors. This should give high levels of fat deposition, but the limited supply of glucose or its precursors may still result in an excess of acetate production relative to its utilization. Fishmeal (FM) supplementation of silage diets tends to stimulate silage intake and liveweight gain probably due to an increased protein supply and improved energy/protein imbalances in the rumen, but its effect on lipid metabolism has not been fully elucidated.