Copper toxicity is not uncommon in sheep. It can be a primary toxicity caused by ingestion of copper containing plants or maladministration of copper containing products; however it is more commonly a secondary toxicity due to liver damage. In the Central West of NSW this is most commonly due to ingestion of common heliotrope (Heliotropium europaeum) growing on stubbles after summer rain. The toxin, pyrrolizidine alkaloid, is also found in Paterson’s curse (Echium plantagineum) and fireweed (Senecio madagascariensis). The later does not occur in the Central West. Crossbred and British-breed sheep are more susceptible than Merinos.
Clinical signs appear suddenly and are due to a haemolytic crisis, usually associated with a stressful trigger. Sheep are generally observed off by themselves one day and then dead the next. Signs in affected animals include depression, lethargy, weakness, recumbency, anorexia, dyspnoea, pale mucous membranes, hemoglobinuria, and severe jaundice.
The carcass is extremely jaundiced. The kidneys are swollen and a gunmetal colour. The urine is a port-wine colour, and the spleen enlarged. The liver is enlarged and friable.
Treating a clinically affected animal is unrewarding. Preventing ongoing losses from the haemolytic crisis that results when copper is suddenly released is aimed at stripping out the copper that has accumulated in the liver. Molybdate drenches and loose licks can be used for this purpose. As outlined in the APVMA permit, a mix of 1000g sodium sulfate and 400g sodium molybdate as mixed in 5.0L of hot water is sufficient to treat 500 sheep with 2.0g sodium sulfate and 0.8g sodium molybdate per sheep when given using standard equipment as a single oral drench of 10 mL per sheep. It is recommended that the drench is used while still warm and that the container is shaken regularly to prevent the active constituents from precipitating out of solution. The prepared drench should be used within 48 hours and repeated at weekly intervals for up to three treatments if necessary.
The APVMA site also mentions a loose mix of 3000g sodium sulfate, 240g sodium molybdate and 4.5kg common salt, which is sufficient to treat 100 sheep with 30g sodium sulfate and 2.4g sodium molybdate per sheep. This mix should be administered as a well-mixed loose lick in open troughs. Do not repeat this treatment until at least three weeks has passed.
Withholding Periods for this treatment are as follows:
MEAT: DO NOT USE less than 8 weeks before slaughter for human consumption.
MILK: DO NOT USE in lactating ewes where milk or milk products may be used for human consumption.
Export Slaughter Interval (ESI): SHEEP: DO NOT slaughter for export less than 8 weeks after last treatment.
It is important to note this treatment is potentially only a short-term solution and success of treatment will depend on the degree of liver damage. Prevention is by minimising intake of heliotrope and other plants containing pyrrolizidine alkaloids.