High-yielding dairy cows must produce large amounts of milk of a desired quality from a cost-effective diet in order for the farmer to remain in profit. Optimal rumen function and health is a key part of the process of converting nutrients into milk efficiently. Essential oils are steam-volatile or organic-solvent extracts of plants that have been shown to have beneficial effects on human digestion. They are mainly cyclic hydrocarbons and their alcohol, aldehyde or ester derivatives (Wallace, 2004). ‘Crina Ruminants’ is a blend of such essential oil compounds, designed to stimulate rumen activity and boost the population of beneficial microbes, through anti-microbial and digestive stimulant activity. In particular, it is believed to encourage an increase in fibre-fermenting bacteria and to counteract the acidotic rumen conditions that can be caused by feeding high starch diets. The aim of this experiment was to evaluate the effects of ‘Crina Ruminants’ on intake and milk production.