Sheepherder CSI

About 10 days ago, while I was making my morning check of the breeding flock and feeding the livestock guardian dogs, I came upon a ewe (one of our daughter's) who was obviously not doing well. She was off by herself (which our sheep typically do only when sick or giving birth). As I watched her lay down from 75 yards away, she looked uncoordinated. When I approached her, she failed to get up and move away - and when I did get her up, she staggered a few steps and fell over. This prompted an immediate call to the veterinarian (who also happens to be my wife). As the ewe was only about a month away from giving birth, Sami decided to come check on her. We determined that she had a fever, and Sami noted a fair amount of nasal congestion. We also noticed that she was turning her head to the left and grinding her teeth. While Sami couldn't be certain, she suspected a combination of an upper respiratory infection and perhaps ovine polio (caused by a Vitamin B deficiency). Sami treated her and we slowly walked her up the hill to the corrals, where we left her in a pen by herself. Later in the day, Sami checked on her and reported that she seemed about the same. We decided we'd haul her home so we could watcher more closely. By the next morning, she was dead - as were the two lambs she was carrying.

When we experience an unexplained death loss, especially this close to lambing, we often take the dead animal to the California Animal Health and Food Safety (CAHFS) Lab at the UC Davis School of Veterinary Medicine. Not only is it cheaper to have an autopsy performed on a dead sheep than it is to have the rendering company remove the animal, we often get valuable information. In the case of this particular ewe, we found out that she died of an unusual case of meningitis (a rare condition in mature sheep). While we were reassured that she didn't have a condition that was likely to spread to the rest of the flock, an additional (and unrelated) finding did concern us. In checking her liver for heavy metals, the pathologist at CAHFS found that she had elevated copper levels (she had 260 ppm of copper; the high end of normal is 100). Copper is an essential micronutrient for sheep, but excess copper can be extremely toxic. Sheep store copper in their livers. When sheep undergo some type of stress (like a difficult lambing, harsh weather, or abrupt change in diet), their livers shed this copper into their bloodstream, often with fatal consequences.

When we read the results, we obviously became concerned about the copper levels in the rest of the flock. If this ewe had elevated copper, it was entirely possible that other ewes may have elevated levels as well. If so, we might have problems during lambing. Sami and I, along with our partner Roger, immediately went into Sheepherder CSI detective mode. Roger and I began researching possible sources of copper, as well as potential treatment options. Sami and I made plans to draw blood samples from a subset of the ewes.

Fortunately, I also placed a call to a friend who is on the faculty at the Vet School. Dr. Bret McNabb is a very experienced and knowledgeable large animal clinician and teacher. He told us that blood tests would not be a good indicator of copper status - we'd need more expensive liver biopsies. He also told me that he usually didn't see copper-related deaths until liver levels were above 400 ppm. He encouraged us instead to continue looking for potential sources of copper in our flock's diet, and to send any additional fatalities to the CAHFS lab. We also talked about treatment options, which included providing supplemental molybdenum to bind the copper that the ewes had already stored.

With Dr. McNabb's reassurance, we turned our focus to sources of dietary copper. We have a couple of suspects:

1. The annual grasses that feed our sheep this time of year likely have some copper in them. Roger went back through some forage tests from the Sierra Foothill Research and Extension Center and found that at some times of the year, the forage may contain slightly more copper than the sheep need.
2. For at least half the year, our sheep graze on land that was once in orchards. Copper sulfate may have been used as a dormant spray on this land; we may have residual copper in the soil. Our next step will be to test the forage for copper during the grazing season (spring, summer and early fall).
3. We utilize surface water  to irrigate our summer pastures and to provide drinking water to the sheep during most of the year. To control algae in their canals (which can clog our sprinklers), our water agency uses one of several aquatic herbicides in which copper is an active ingredient. While both products are labeled as safe for livestock consumption, this may be something we need to investigate further.
4. As Dr. McNabb pointed out, sometimes feed manufacturers make mixing errors. For example, the mineral mix we provide to our sheep does not have any added copper. However, mistakes can happen. This weekend, we sent a sample of our mineral mix to CAHFS for analysis. We should know the results by the end of this week.
5. The weed common groundsel (Senecio vulgaris) contains a liver toxin that apparently inhibits the liver's ability to metabolize copper. We know we have common groundsel in areas where the soil has been disturbed, and we know the sheep will graze it on occasion. However, according to Toxic Plants of North America (Burrows and Tyrl 2001), sheep and goats are less susceptible to common groundsel than other livestock - and can actually be used to control it. Not exactly a smoking gun...

For now, the source of copper remains a mystery. The rest of the flock seems healthy, so we're hopeful that this ewe's copper levels were an anomaly. We'll definitely investigate any subsequent death losses - we're fortunate to have the CAHFS lab close by. And we'll continue to investigate the potential sources outlined above. Stay tuned.... And if you've had similar experiences with your sheep, please let us know!