Prevention of selenium deficiency in grazing animals by annual topdressing of pasture with sodium selenate.

The effectiveness, safety, economics and methodology of selenate prill topdressing in preventing selenium deficiency in grazing stock under various farming conditions on all groups of deficient soil are reviewed. Topdressing at the approved rate of 10 g/ha Se is effective for 12 months, and has a toxicity safety margin of about 20 times. This compares favourably with selenium dosing. However, materials for dosing usually cost less than one-sixth of those for topdressing. Considerations of convenience, correction of soil deficiency, and production profitability make topdressing an alternative for some farmers; particularly with severe deficiency, and a high stocking rate. Topdressing costs are least where one-sixth or less of the farm can be treated and grazed continuously for 2 months or more; as by ewes at mating. At the very small approved rate no adverse effects are foreseen on human or animal health, export sales, or the environment.