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 19 87 to pasture at Bakers Hill in Western Australia at 10 g Se ha-1. Mer ino wethers grazing the pasture over the following 3 years had signifi cant increases in liveweight and wool production even though the contr ol sheep showed no clinical symptoms of selenium deficiency. Sheep tre ated with selenium intra-ruminal pellets that also grazed the selenium -fertilized pasture showed no signs of toxicity and also had significa nt increases in liveweight and wool production. There was no significa nt increase in wool fibre diameter from the selenium treatments. Respo nses to blood selenium indicated that whole blood selenium should be m aintained at a minimum value of 60 mug Se L-1 or a minimum plasma conc entration of 40 mug Se L-1 to avoid subclinical selenium deficiency.