The element copper is essential in small quantities. However, increased amounts of copper are toxic and sheep are particularly prone to copper poisoning, more so than other farm animals such as pigs or cattle. Most cases are chronic caused by the build up of copper derived from the animal’s diet. Rarely cases of acute copper poisoning occur owing to the incorrect use of therapeutic copper injections.
In sheep, the element molybdenum controls the metabolism of copper intake. If the sheep’s diet is deficient in molybdenum and it is grazing on an area with a high copper it will absorb copper, which is then stored in the animal’s liver. If the molybdenum level is in excess of 1 ppm then sheep do not absorb toxic levels f copper. The interaction of molybdenum in copper poisoning is further complicated by sulfates present in the soil. High sulfates levels causes the formation of insoluble molybdenum sulfate, which yields plants with low molybdenum levels.
Liver copper levels in excess of 500 ppm are considered toxic. If the animal becomes stressed in some way, the stored copper is released into the blood stream and the sheep starts to exhibit signs of copper poisoning. Stress in sheep occurs in a number of ways including poor nutrition, transport and even the weather. Some cases occur when the ability of the liver to hold the excess copper is exceeded resulting in a rapid release of copper into the blood stream.
Copper released into the blood ruptures some red blood cells and has an adverse reaction on hemoglobin changing it to methhemoglobin. Methhemoglobin cannot carry oxygen and the animal exhibits signs of anemia, becoming lethargic with pale mucous membranes. The sheep rapidly becomes jaundiced and the mucous membranes take on a yellow color and its urine becomes dark sometimes appearing black in color. In severe cases, sheep die before the jaundice becomes apparent.
When a veterinarian diagnoses copper poisoning in sheep, they start a series of molybdenum treatments using either oral or injectable ammonium tetrathiomolybdate. This treatment encourages the sheep’s metabolism to excrete the excess copper poisoning their system via their kidneys.
Prevention of such poisoning requires vigilance and care by the farmer. Some animal feeds contain copper supplements these are unsuitable for sheep unless they have been diagnosed with swayback caused by copper deficiency. The feed given to pigs is quite high in copper and they excrete high levels of copper in their feces. Using slurry from pigs to manure fields used for sheep grazing can cause copper poisoning. It is possible to obtain measurements of the levels of copper and molybdenum in the grazing used for sheep. If the molybdenum level is low, then adding a molybdenum supplement to feed prevents copper poisoning.
This article is for information only and not a guide to diagnosis or treatment. Diagnosis and treatment of copper poisoning is sheep requires consultation with a qualified veterinarian.
Chronic Copper Poisoning in Sheep - Dr. S. John Martin - Veterinary Scientist, Sheep, Goat and Swine/OMAF
Copper Poisoning in Sheep Neil Sargison BA VetMB DSHP FRCVS – NADIS disease bulletin