dose rates should not be increased above the recommended levels because of the risk of selenium toxicity. One injection will give adequate selenium for a period of 30 to 60 days in most instances. The injections can be repeated. The withdrawal period is 30 days.
Selenium can be compounded into the total ration to an added level of 0.3 parts per million on a dry matter basis according to current federal regulations. This form of supplementation is ideal for housed cattle but has obvious limitations in pastured cattle.
Current federal regulations allow selenium to be added to the salt/mineral mix at a level of 120 parts per million for cattle and 90 parts per million for sheep. Supplementation of the salt/mineral mix is a more convenient method of selenium supplementation for cattle on pasture than repeat selenium injections. However, salt intake can be quite variable within a group of animals and there can be considerable variation in the degree of correction obtained. In the Pacific Northwest salt supplementation at this recommended level frequently failed to correct the selenium deficiency.
With all methods of supplementation the efficacy of the level of supplementation, and in the case of injections the duration, should be monitored by whole blood selenium or glutathione peroxidase analysis. It should not be assumed that because supplementation has been instituted the deficiency has been corrected.
The toxic dose of selenium by injection for both cattle and sheep is in the region of 1 mg/kg. Acute selenium poisoning may be produced in lambs given a single injection of 5 mg of selenium. This can occur when the wrong selenium preparation is used for injection and with over generous administration. Signs of acute selenium toxicity include blindness, abdominal pain, excessive salivation, paralysis and death after 1 to 7 days. Post mortem examination reveals excessive fluid in the lungs and pleural cavity.
Copper deficiency may occur as a simple deficiency where the concentrations of copper in the diet are markedly deficient. Copper deficiency can also occur as a conditioned deficiency and in this situation copper concentrations in the diet may be marginal to normal but other constituents of the diet interfere with absorption and utilization of the ingested copper. Prominent amongst these are molybdenum, sulfur and iron. Copper deficiency most commonly occurs, as a conditioned deficiency in Washington State and this is