Although high genetic merit dairy cows are capable of peak yields in excess of 50 kg per day these are seldom maintained primarily due to an inability to satisfy energy requirements. Fats and oils are often incorporated into rations as a means of increasing dietary energy content. However, unless included at relatively low levels or in a protected form, lipid supplements may adversely affect fibre degradation in the rumen. The current data are derived from a study conducted to evaluate the potential of an in vitro model to assess the effects of oil supplements on forage organic matter degradation (iOMD).