How much rumen-active fat can be included in diets

Only a relatively small concentration of rumen-active fat (around 3-5% fat in the ration dry matter) is tolerated in the rumen before problems can begin to occur. This varies with type of fat, fibre concentration of the diet and how the fat is supplied e.g. as rumen-active oils such as fish oil or as a more slowly-released component of oilseeds.

Jenkins (1998) proposed a simple approach to determine the maximum feeding rate of any rumen-active fat, expressed as a percent of the ration dry matter, based on multiplying 4-times ration neutral detergent fibre (NDF) concentration and then dividing by the unsaturated fatty acid content of the fat supplement. An important limitation of the equation is that it is only intended for rumen-active fats having unsaturated fatty acid proportions of 40% or greater.