Copper Poisoning in British Soay Sheep

This summer (2012) two of my British Soay sheep died of copper toxicity. As they were not exposed to feed labeled for other species that might account for the excess copper in their systems, it became an investigation of all feed sources and discussions with veterinarians, breeders and other professionals across the country and the UK to determine the cause of the copper toxicity and the treatment.

Chemistry was never a strong suit of mine, so this has been a steep learning curve for me.  However it has given me a greater appreciation of the complex interactions minerals play in maintaining the delicate balance of health in our sheep. Hopefully sharing this information with other British Soay keepers will increase awareness for the need to monitor copper levels as an important part of managing our sheep.
As a primitive breed, the Soay is one of the most sensitive to copper and very susceptible to copper toxicity. Copper is an important component of their diet in extremely minute amounts but it can accumulate in the liver over a period of time with no outward symptoms. When the sheep experience stress, the stored copper can be released into the blood causing the poisoning.  The symptoms that I observed in my sheep that died included going off their feed,  head pressing in the corner, depression, weakness, disorientation (possibly blindness) brown urine and very high temperatures with a very rapid decline and severity of symptoms. I have since learned that the brown urine is caused from the breakdown of the tissue in the kidneys from the overload of copper.  When checking the eyes of the affected sheep, I noticed the inside of their lower lids to be red in color.  At the time, I thought this indicated that they were not anemic; however I have since learned that bright redness is an indication of hemorrhaging. I also noticed that these sheep kept away from the others and in both cases, I witnessed the other ewes pushing them away from the flock.  These symptoms developed rapidly, within a matter of hours and once they started, the sheep were dead within two days.  Although the literature describes jaundice as being a symptom, this was not something that I noticed in my sheep.

In the first instance, the ewe (age 3) died approximately 6 weeks after delivering a stillborn lamb.  In the second, the ewe (age 9) died while we were experiencing extreme and extended heat conditions in this area.  In addition, she had unusually not lambed this year, despite being put in a breeding group.  (There was some speculation that she may have miscarried early on) In both cases, these were stresses that may have triggered the release of stored copper from their livers.

Chronic copper poisoning can occur from excessive copper intakes or from low intakes of molybdenum, sulfur, zinc or calcium. Although it is important to check feed labels for copper and only use feed that is labeled for sheep with no added copper, the accumulation of copper over time can occur in British Soay from feed with nutritional standards that have been set for commercial sheep. The sensitivity to copper and susceptibility to copper toxicity in Soay makes this an important management issue.  Sheep products provide a list of ingredients but not all products provide mineral levels.  Even if copper is not listed as an ingredient, it can be a trace element contained within ingredients.  It is therefore important to question producers and request mineral levels for products purchased for Soay consumption.

I contacted the Feed Coop where I purchase my sheep feed and they checked the lot numbers to make sure that the products I used were labeled correctly and the copper levels were within the allowable limits.  Although there was no added copper to the feed or mineral, it is found naturally in some of the ingredients. The feed and mineral were each found to be at 15ppm which is below the allowable limit of 30 ppm.  However this level is based on the copper tolerance in commercial breeds of sheep.  In addition, our water was tested and found not to contain any copper.

Although we suspected that the sheep feed and mineral being used was providing too much copper, this was not the entire story because copper absorption is affected by other minerals as well.  Dietary molybdenum levels also affect copper requirements. Molybdenum bonds with copper preventing its absorption. So in geographic areas where copper is naturally high in hay, a higher level of molybdenum is necessary to prevent excess copper being absorbed. In my area copper levels are high and molybdenum levels are low which was reflected in my hay. Sulfur is also an important mineral.  Sulfur and molybdenum combine in the rumen to make copper less available for absorption in the intestine.  Higher sulphur percentages in the diet also help lower copper levels.  Further investigation revealed that hay grown east of the Mississippi contains more copper than hay grown west of the Mississippi.

Although it is not possible to determine the amount of copper being stored in the liver without a liver biopsy, the blood serum levels give an indication of how much copper is in their systems.  We decided to find out what the blood serum copper levels were in the live sheep so blood samples were taken from seven ewes of various ages.  Two samples were run individually, while the other five samples were pooled, giving an average. The analysis of the blood samples showed high levels of copper in all the sheep tested. (1.4-1.5 ug/ml). Three sheep who were exhibiting a change in behavior which made us suspicious that they might be in the early stages of copper toxicity, were treated with a drench containing sodium sulfate and molybdate once a day for five days.

Since the pooled blood serum levels were high but not toxic, my veterinarian recommended that the rest of the flock, who were behaving normally, be treated with a specially formulated mineral supplement once we knew the right combination of minerals.  He recommended that I not drench them at this time as we did not want to end up creating a mineral imbalance in their system by treating them before we had all the information.  In addition with breeding season fast approaching, my veterinarian thought that some of the copper in their systems would be taken up by the developing fetus. 

To determine how much copper my sheep had absorbed since coming to Wisconsin, blood samples were taken from six British Soay that had just arrived from Oregon. The samples taken from the new arrivals were pooled and the results showed an average of 1.2 ug/ml copper which is considered adequate and was considerably lower than my other sheep.
Keepers of British Soay sheep should become familiar with copper and molybdenum levels in the soils of their area and in their local hay.  Besides too much copper, too much molybdenum can create a copper deficiency and an imbalance of minerals, which comes with its own set of problems.

In order to know the appropriate minerals to supplement my sheep with, a core plug was taken from several hay bales to analyze for copper and molybdenum levels.  The hay that I have been using comes from a local hay producer who does not use any manure on the fields and he doesn’t keep any livestock himself.  Soil and growing conditions in the area produced higher copper, low molybdenum and sulfur.
The results showed copper at 12.7ppm, molybdenum at .023ppm and sulfur at 0.27%. . The copper levels were thought to be relatively high, but with such a low molybdenum level it made the absorption of copper even greater. There was nothing preventing the copper from being absorbed in their system.  This meant going forward that I needed to find a mineral supplement that contained a higher molybdenum and sulfur content to reduce the amount of copper available for absorption.

My veterinarian determined what minerals my sheep needed in their diet and after some searching found a mineral and salt product that suited my needs and was available from my feed store. Since the sheep had been off minerals for a while, the new minerals were introduced gradually to prevent them from consuming too much all at once.

Since discovering that the sheep feed I was using contained copper, I have not been providing any supplemental sheep feed.  Now with breeding season fast approaching and temperatures beginning to fall, I have started giving my ewes beet pulp mixed with oats and barley. I haven’t given this mixture to the rams because I was concerned that it might cause urinary problems.  The rams seem to be doing fine on just hay.  Since introducing the new mineral salt, the ewes seem to eat up their ration very quickly, while the rams are not as interested.  I suspect this behavior may relate to ewes being more susceptible to copper toxicity than rams since they now appear to crave the minerals salts that are the remedy.

Copper is not all bad!  Copper is essential for the development of healthy newborn lambs, wool production, and required for an effective immune system.  Sheep need some copper, but mature Soay ewes seem to be more vulnerable to toxic levels of copper.

As we go forward, future hay deliveries will be tested for copper/molybdenum levels and minerals salt supplement adjusted accordingly.  In addition, periodic blood samples will be taken from the sheep to monitor their serum levels.
Many thanks to the breeders, scientists, veterinarians and friends (in the US, and the UK ) who have contributed their time, expertise, and ideas to solving this problem and coming up with a practical solution to managing copper levels in British Soay with the geographic conditions that exist in this area.  Special thanks to Dr. Ray Pawlisch from Brodhead Veterinary Medical Center for his tireless persistence to finding a treatment that was practical and safe and for his patience explaining all of this to me.