No previous symptoms, just a dead animal in the middle of the field. Then, the next day, a second one.
These were well-conditioned animals in midgestation on excellent fall pastures, otherwise healthy with no signs of diseases, predators or gunshots. We were puzzled. As I walked through the fields and looked down into the grass, however, I noticed something unusual: lots of mushrooms, many more than I had ever seen previously.
Also, under the trees, lots and lots of mushrooms. This autumn had been a particularly good mushroom season. All types – white, grey, yellow, orange, some with caps, some just straight like delicate fingers. A botanist would have a delightful field day identifying them, but I’m a livestock nutritionist. I’m thinking: toxicity. Some mushrooms kill animals.
Toxic mushrooms are fascinating, and there are reams of reports documenting mushroom-related deaths in livestock and humans. Mushrooms, by the way, are not actually stand-alone plants. They are the aboveground fruiting bodies of fungi organisms that thrive in the soil, trees, decaying logs and other places. Fungi contain no chlorophyll and are classified in their own huge kingdom that also includes yeasts and molds. Fungi manufacture a vast array of unusual compounds, and many are quite toxic.
Some troublesome fungi are the mycotoxins in grains, ergot in some grasses, forage endophyte in tall fescue, the pithomyces fungus in dead grass that causes facial eczema, the “magic” mushrooms like psilocybin with their hallucinogenic compounds similar to LSD and the fungi that cause a multitude of livestock diseases from abortion to ringworm (club lamb fungus). This month, however, we’ll confine our discussion to the spectacularly bad ones: the deadly mushrooms that contain some of the most potent toxins on earth.
While mushroom enthusiasts can gladly make a long list of toxic species, the mushrooms responsible for the vast majority of poisonings in temperate climates belong to the genus amanita. Some of their common names tell the story: death cap (Amanita phalloides), destroying angel (A. virosa), fly agaric (A. muscaria) and panther mushroom (A. pantherina). Botanists have identified nearly 1,000 species in the amanita genus, and only a few of these have been carefully analyzed for secondary compounds. Many amanitas, including the well-known toxic species, are unfortunately rather common.
Some amanitas contain a veritable cocktail of toxic compounds. Amanita phalloides is the most famous species, for good reason, as it contains amatoxins, phallotoxins and verotoxins. These relatively small molecules are cyclic peptides, which means they are composed of amino acids arranged in a ring. The amatoxins have eight amino acids; the other two have seven. Some of these amino acids are quite unusual and not found in mammals. In any case, the amatoxins are pure poison – they act by blocking the enzyme RNA polymerase II, which is critical for synthesizing messenger RNA in all cells.
Blocking this enzyme effectively stops all protein synthesis in these cells because messenger RNA transmits information from DNA to the cellular ribosomes where the protein synthesis occurs. The result: cell death, rather quickly. And some of the first cells affected are in the liver which is so critical for proper functioning of many systems in the body. The phallotoxins and verotoxins are also highly toxic, but they are not easily absorbed from the GI tract, so they are less important.
That’s not all. The amanitas contain other toxins. One unusual molecule in the fly agaric is amavadin, which is built around an atom of vanadium. While vanadium is not a required nutrient in mammals, in this mushroom it occurs in concentrations 400 times higher than in other plants. Fly agaric also contains ibotenic acid and muscimol, which affect the central nervous system and cause hallucinations – an effect that has been known (and sometimes used in religious rites) for centuries.
When trouble hits
Let’s leave the biochemistry and address the practical situations in the field. Few people are more practical than veterinarians, and they classify toxic mushrooms in a very straightforward way: by the length of time it takes to show symptoms (“the latency period”). If symptoms appear relatively quickly – within three hours after ingestion – then the animal will feel very bad, but it will probably survive. Those toxins act rapidly, but they generally do not cause permanent damage and are quickly detoxified and excreted from the body.
In contrast, if the first symptoms don’t begin until more than six hours after ingestion, this is probably bad news – because a long latency period is usually due to the amatoxins. These molecules are absorbed across the gut wall and then transported to the liver and other organs. Once inside the cells, the toxin begins to lock up protein synthesis, and this takes many hours to show effects.
Meanwhile, the animal (or human) shows no symptoms. But as things metabolically deteriorate, physical symptoms begin to appear: primarily vomiting and abdominal pain. Then, surprisingly, the animal’s symptoms subside for a time, an apparent remission. However, all is not well; the animal is not better. A few days later, the true effects of the accumulated cell damage take effect, with complete liver and kidney failure, jaundice, coma and finally, death.
And it doesn’t take much toxin to kill. The amatoxins are astonishingly potent. The medical literature lists the lethal dose at only 0.1 milligram per kilogram bodyweight for all livestock species. Which means that it takes only 64 milligrams of amatoxin to kill a 1,400-pound cow. And only 7 milligrams to kill a 160-pound ewe (or human). How little is this? For reference, consider that 1 ounce equals 28,349 milligrams, and even a dime weighs 2,268 milligrams. In practice, the 7 milligrams of amatoxin to kill a ewe or human would be contained in only one-half a cap of a death cap mushroom. And an adult cow would need only two to three caps of these mushrooms. Not very much.
Treatment options
More bad news. Are there antidotes for these toxins? No. Vaccines? No. What about treatments? Not much. The veterinary and medical books are pretty consistent: treatments seem to be symptomatic and supportive. Which means that we try to reduce the symptoms and make the animal feel as comfortable as possible. We strive to keep the animal alive long enough so it can clear the toxin and repair the organ damage. And for humans, one of the last resort techniques is a liver transplant. Not exactly a comforting thought.
Let’s return to the ranch with those two dead cows. Could they have consumed toxic mushrooms? Possibly. In general, we don’t think livestock will actively seek out and eat toxic mushrooms, but we don’t really know much about the palatability of each species. (On the other hand, we do know for certain that some mushrooms are delicious, like chanterelles, and there are some reports that the death cap mushroom may actually have a pleasant taste.)
Some possible scenarios: What if tiny mushrooms were hidden in a dense sward of grass, and as the animal grazed it actively, some fungus pieces could conceivably end up in a few mouthfuls? Another possibility: feeding hay or balage on a field, if the mushrooms were growing up through the vegetation and were consumed as the animals ate the hay? Or young lambs or calves exploring an area at the edge of a pasture or under some trees, especially if they were curious or hungry? The long latency period adds to our uncertainties. On a farm or ranch, there are a lot of potential scenarios. And there’s a lot we don’t know.
So when we lose animals suddenly, with no obvious causes, I think we should add the possibilities of toxic mushrooms. We should also find out if they exist on our farms. Grab a mushroom guide, spend a quiet afternoon in a field or in the woods, looking and comparing. These mushrooms are fascinating. Just don’t taste them. 
ILLUSTRATION: Illustration by Kristen Phillips.
Woody Lane, Ph.D., is a livestock nutritionist and forage specialist in Roseburg, Oregon. He operates an independent consulting business and teaches workshops across the U.S. and Canada. His book, From The Feed Trough: Essays and Insights on Livestock Nutrition in a Complex World, is available through Lane Livestock Services.
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Woody Lane, Ph.D.
- Lane Livestock Services
- Roseburg, Oregon
