SELENIUM FERTILIZERS FOR PASTURES GRAZED BY SHEEP .2. WOOL AND LIVEWEIGHT RESPONSES TO SELENIUM

Two forms of selenium fertilizer, Na2 SeO4 (quick release) and BaSeO4 (slow release), prepared by Mintech of New Zealand, were applied in 1987 to pasture at Bakers Hill in Western Australia at 10 g Se ha-1. Merino wethers grazing the pasture over the following 3 years had significant increases in liveweight and wool production even though the control sheep showed no clinical symptoms of selenium deficiency. Sheep treated with selenium intra-ruminal pellets that also grazed the selenium-fertilized pasture showed no signs of toxicity and also had significant increases in liveweight and wool production. There was no significant increase in wool fibre diameter from the selenium treatments. Responses to blood selenium indicated that whole blood selenium should be maintained at a minimum value of 60 mug Se L-1 or a minimum plasma concentration of 40 mug Se L-1 to avoid subclinical selenium deficiency.