The use of inoculants to improve the performance of animals is practised widely in many intensive animal production industries, but this practice is less widespread in the extensive grazing systems. Here we describe the background and some recent developments in the area of utilizing ruminal micro-organisms for the modification and improvement of productivity in ruminants. The inoculants, designed for establishment in the new domestic ruminant host, have specific, superior or modified activities, but currently have a restricted geographical or species distribution. Current work has focused on three novel or augmented activities, namely: reducing the toxicity of particular plant poisons, increasing the utilization of plant fibre and the modification of protein supply. The most successful projects so far have tackled the detoxification of the plant poisons, mimosine and fluoroacetate, but projects aimed at increasing the utilization of plant fibre are now well advanced. Molecular techniques have significantly assisted in the identification, differentiation and tracking of organisms and are essential for the construction of modified organisms.
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