Trace mineral supplementation of feed rations is commonly achieved by the addition of simple inorganic salts. The bioavailability and hence the performance enhancement achieved by trace mineral supplementation is significantly improved if the metal is added in the form of a peptide complex or chelate. Extracts from the Yucca shidigera plant bind ammonia in-vivo and thus may alter rumen fermentation and in turn milk synthesis. The aim was to determine the effects of a supplement (All-Plex, Alltech Ireland) included at 10g/day, on milk yield, milk composition, somatic cell counts (SCC), reproduction parameters and blood copper, zinc selenium and haemoglobin. The supplement contained proteinated minerals (100mg copper, 300mg zinc, 300mg manganese, 2mg selenium) and a yucca extract (1g Dc-Odorase, Alltech Ireland).