Copper Toxicity in Pygmy Goats
Reviewed by Dr. William Holleman
|There is no harder lesson than losing a beloved animal
to something preventable. I lost
GCH Raz Zoo's Honest Abe, a favorite buck, to copper toxicity, an obscure ailment not
easily understood. Our trace mineral salt was the main culprit. This article was written
in the hope that you will be able to avoid such a loss.
Goats require dietary protein, energy, fiber, water and essential macro- and micro-minerals nutrients. Balancing these needs is a matter of discovering what your goats need and in what quantities. Each geographic region may be different in its needs, and selenium is a good example of this. Some regions have high levels of selenium in their forages while others have too little. Your goats' nutritional management is very dependent on where you live.
There are several more considerations when deciding on an appropriate diet for your goats, including individual metabolism. Some goats are easy keepers and tend to gain weight easily, while others remain slim. Their metabolisms are simply different and their needs are different. Metabolism, environment, diet, vaccinations, and general health are just a few specific factors that play a role in copper imbalance. Dietary intake of copper and molybdenum, a copper-binding metal, are perhaps the most important. Both affect the absorption and excretion of each other. When excess amounts of molybdenum are present in the diet, copper deficiency is a possibility. When the diet is low in molybdenum, there is the potential for copper toxicity.
The ratio of copper to molybdenum should average 10:1, with no more than 20 ppm of copper in the daily diet. Dr. Patricia A. Talcott, a Veterinary Toxicologist at the University of Idaho, says "Copper metabolism and utilization appear to be influenced by many different factors related to the animal (breed, age, size, concurrent diseases), environment (weather, stress), and diet. All factors need to be considered when determining how much copper an individual animal can tolerate. In general, it is not recommended to exceed 20 ppm copper in the total diet of goats." If this level is drastically increased, copper accumulates in the liver until a stressful event or illness causes the copper to leave the liver and enter the blood stream. Chronic copper toxicity is like a bowl of water that has one drop of water at a time added to it - there is no sign of a flood until the last drop causes the water to spill over. In chronic copper poisoning the liver retains copper until it reaches its threshold and then dumps enough copper into the blood stream to cause toxic levels. Acute copper poisoning is when a goat experiences toxic doses of copper in a short period of time. Chronic copper toxicity becomes acute in the final stages.
The onset of symptoms can be alarmingly quick and extreme measures are needed. Prognosis is guarded. Animals can appear to be normal before symptoms are noted. The goat may appear a bit depressed with a lack of appetite, but there may be no overt symptoms until the animal reaches the acute stage when it suffers a sudden hemolytic crisis. Symptoms include jaundice, discolored (brick red) urine that is due to destruction of the red blood cells, inability to stand, shaking and/or difficulty with breathing. Other symptoms may include brown mucous membranes, diarrhea, arched back (due to pain) and grinding teeth.
Until the time of hemolytic crisis the serum titer for copper will be normal, so it is nearly impossible to diagnose beforehand. Blood analysis can be informative for other mineral and vitamin deficiencies or excesses, like selenium and vitamin A, but not for copper. Normal values for serum copper are from 0.70 to 2.00 parts per million. A goat may have normal values just before copper toxicity becomes acute. Monitoring copper levels in the herd is difficult; liver biopsy is the only way to determine hepatic copper levels. It is an invasive and dangerous procedure, and testing is usually done after death.
The standard treatment for copper intoxication is daily drenches of 100 mg ammonium molybdate and 1 g sodium sulfate in 20 mL water, or an equivalent amount in feed if the goat is able to eat. This therapy is recommended for at least 30 days. Cuprimine® is a fast-acting treatment, but it is expensive. Veterinarians don't usually stock Cuprimine, but it is a human drug used to treat several diseases, and your veterinarian could get it or write a prescription. Curprimine (Peniciliamine) binds copper so it can be harmlessly excreted in a non-toxic form. IV fluids may also be helpful in washing toxins from the blood system. Regardless of the treatment chosen, the diet must be examined and changed to avoid further imbalances. Sources of excess copper should be identified and removed, and molybdenum may be added to feeds. Trace mineral premixes should be custom-made to exclude copper. Sheep minerals exclude copper because sheep are very sensitive to it.
Trace mineral salt is not the only culprit that may cause problem. Goats are more prone to copper poisoning when their diet consists of feeds manufactured for other species, especially dairy cattle and horses. These species can tolerate much higher levels of copper and lower molybdenum than sheep and goats. Check the labels for copper content on all feeds and supplements. In one well-researched case, a pygmy buck died of copper toxicity from eating rabbit pellets. In another, trace mineral salt high in copper was found to be the culprit.
Further studies give us a general background to copper susceptibility in goats. In Chronic Copper Toxicity in Nubian Goats, Journal of Comparative Pathology, 1977, 87:4, 623-627, 7 ref., six Nubian goats were given oral doses of copper sulfate at 20, 40 and 80 mg/kg/day. Two goats died within 54-68 days of copper poisoning and four others were killed within 123 to 144 days with elevated levels of copper.
In another study, The Effects of Intravenous Injection of Small Amounts of Copper Sulfate in Nubian Goats, Journal of Comparative Pathology, 1976, 86:3, 387-391; 7 ref., 50 mg of copper sulfate was administered IV on each of three consecutive days to five Nubian goats; three goats died within 3-4 days and the remaining survivors were killed after 38 days.
In a comparative study of chronic copper poisoning in lambs and young goats, death in the lambs occurred on day 67 and 88. The experiment ended after 20 weeks. No goats died, but they had increased copper levels and average concentrations were lower than those of sheep.
Chronic Copper Poisoning in Angora Kids, New Zealand Veterinary Journal, 1989, suggests that goats supplemented intramuscularly with selenium accumulate more hepatic copper then control animals. Further, goats given selenium IM develop chronic copper poisoning at lower levels of hepatic copper than in previously-reported experimental cases. The study states: There is still much to be learned about both the levels of dietary copper which goats can tolerate and the interplay with other dietary factors, but it seems possible for well meaning goat owners to kill their animals with kindness in this way.
In Treatment of Copper Poisoning in Goats by the Injection of Trithiomolybdate, Small Ruminant Research, 1992, 8: 1-2, 31-40, 24 ref., 27 goats of the Jiangsu breed developed acute copper poisoning by IV injection of 2.5 mg of Cu/kg per body weight. The copper poisoning was subsequently prevented by simultaneous IV injection of trithiomolybdate.
Effects of Daily Oral Administration of Copper to Goats, Acta Veterinaria Scandinavica, 1978, 19: 4, 561-568; 10 ref., points to the variability in the goats' susceptibility to copper. Three goats were given copper sulfate solution orally for 56-113 days. One goat accumulated substantial amounts of copper in the liver, developed two separate hemolytic crises and died. The two other goats only showed an increase in copper before they were killed. The results showed that the goats were susceptible to different degrees of repeated copper dosing and that while the one goat was similar in copper susceptibility to sheep, the other two were more resistant.
As mentioned, copper requirements vary with breed and the environment and depend on dietary molybdenum levels. Recommendations for specified levels of dietary copper require consideration of environmental factors such as soil molybdenum concentrations, species of pasture plants, and fertilization practices. Molybdenum and sulfur reduce available copper. Calcium, cadmium, iron, and zinc inhibit copper's absorption. Lime, used as fertilizer, also reduces copper and increases molybdenum uptake by pasture plants. Liming has caused copper deficiency in dairy cows on New Zealand pastures. This may seem terribly confusing but the only thing you really need to remember is that copper can be a deadly toxin for your goats. Read labels for copper content.
The widespread incidence of copper-related problems in goats is currently unknown. Dr. Larry Thompson, a Veterinary Toxicologist at Cornell University, suggests that goats be handled more like sheep in their susceptibility. Although many goats are fed horse and dairy feeds without showing signs of copper poisoning as would be expected in sheep, why take the chance? Most goats on a well-balanced diet do not need copper supplements, except where regional copper deficiencies are well documented.
Toxicity in Sheep (1)
Copper Toxicity in Sheep (2)
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Copyright February 1995