Chronic toxicity results in loss of weight, dullness, sloughing of hooves, and lamenesso Toxicity is rare but occasionally found where cattle on overgrazed pasture are forced to eat a milk-vetch that accumulates selenium. The best cure is to remove the animal from the pasture. A vitamin E deficiency increases the amount of selenium required to prevent this form of nutritional muscular dystrophy. Cows on Se deficient diets may have lower fertility and an increased incidence of retained placentas. The RDA for Se is 200 parts per billion.
Se deficiency is quite common in west-central and northern Alberta.
Se can be added to salt or mineral mixes, or injected. It is used on domestic water supplies to reduce the incidence of tooth decay. Too much FI causes abnormal bone growth, mottling and degeneration of teeth, and delayed growth and reproduction. To avoid excessive consumption of FI be sure any rock phosphate fed is defluorinated. Trace minerals can be effectively supplemented in the diets of cattle by using the proper trace mineralised salt.