The partitioning of fat in ruminants-can nutrition be used as a tool to regulate marbling?

In this paper we propose that regulation of the glucose/ insulin axis by diet will result in increased fattening at the marbling (intramuscular) depot. The pattern of fat accretion in the whole carcass is first described to emphasise that the marbling depot is relatively late maturing. The pathways of fat metabolism are then discussed with the aim of examining the possibility of regulating fat partitioning between depots in ruminants. The importance of acetate versus glucose + lactate as substrates for lipogenesis differs between depots in the ruminant and it is proposed that this might allow for differential control of lipogenesis. The role of diet in the manipulation of pathways for lipogenesis in ruminants is then explored. Both glucose infusion and diets promoting starch digestion in the small intestine increase the activity of enzymes (ATP citrate lyase) associated with lipogenesis from glucose indicating a greater relative importance of glucose as a lipogenic substrate and this may have an impact on the relative growth of different fat depots via the glucose/insulin axis. Chromium supplementation to ruminants consuming a diet low in chromium also increases the relative importance of glucose as a precursor for lipogenesis and causes redistribution of fat away from the subcutaneous site. Finally the effects of feeding different cereal grains and chromium supplementation to 150 day fed steers on visual marbling score are discussed. It is concluded that starch digestion in the small intestine is associated with increased visual marbling score.