Pasture Plants That Poison

Poison Hemlock


I was thrown from a horse twice and tried to stop a runaway once when I was a boy, so I am not particularly enamored by the equine breed. But I worry about horses. I’ve been reading about plants that poison livestock and was surprised to learn that for as big and strong as horses are, they are rather fragile when it comes to eating their vegetables. Among the things that are supposed to be toxic to them are onions. Yep, says so right here in this scientific report I am reading. Also, red maple leaves, acorns, yew foliage, avocadoes (no wonder I don’t like them), hairy vetch, and many others, some of which really raise doubts in my mind, like black walnut foliage, black locust bark, and alsike clover. Alsike clover causes slobbers— excessive drooling— in horses. I sure wish my grandfather was around so I could ask him about that. He grew a lot of alsike clover because it survived on poorly drained soil and his landlord was too cheap to put in tile drainage. I remember when he still farmed with horses. Wonder what he did about slobbers?

There are many other plants that can poison farm animals. We all know that if a wild cherry limb blows down in a storm, it needs to be removed pronto from pastures because the wilted green leaves have cyanide in them in potent amounts. But I would argue that the danger to farm animals from wild plants is being overstated. Maybe red maple leaves when they are first falling from the trees in the autumn are toxic, but I’ve got red maples all over and our livestock have never been poisoned.  Acorns and oak leaves? My sheep love acorns, even red oak acorns which are very bitter, and devour any little oak seedling they find. Mine have access to black walnut foliage too but have never suffered from it as far as I know. The juglone in black walnut is toxic in some ways and veterinarians say that the trees and horses don’t mix. But my neighbor’s draft horse roams all summer in a woodlot full of black walnut trees. In fact, an old remedy for internal parasites in livestock is to soak black walnut hulls in their drinking water. If you think that sounds far-fetched, a much publicized control for internal parasites in humans is black walnut tincture, made from soaking particles of black walnut hull in vodka. Think I’m kidding, don’t you. Google it.

One toxicity study describes cases where horses sickened from gnawing the bark off of black locust fence posts. And black locust foliage is supposed to be slightly toxic too. I know of several instances of cows and black locusts living together without problems, but my main argument comes from my wife’s memories. Her home farm pastures were studded with black locusts and she can’t remember of cows or horses being affected. In fact when the black locusts all died of disease (they are making a comeback now) her father was upset. He liked his black locusts. Nothing makes better firewood or a more endurng fence post.

Seems to me the first question to ask in this case is why a horse would be hungry enough to eat fence posts. I wonder in fact if the problem of toxicity in farm animals comes mostly from forcing them to graze pastures long after all the good grass is gone. They are forced to eat and over-eat toxic plants they normally would avoid.

Also, there are many examples of plants that are actually medicinal in small amounts but toxic in large amounts. Foxglove is poisonous, for example, but science has concocted a heart medicine using the digitalis in it. Poison hemlock supposedly killed Socrates, but when I noticed that my sheep would take a little nibble or two occasionally from plants that had escaped my trusty hoe, and seemed no worse for it, I decided to take a nibble myself. I can vouch that there is nothing in nature as bitter as poison hemlock. The taste alone could kill most of the philosophers I know. No animal is going to eat more than a nibble at a time unless it is starving or wants to die. I have a hunch that the occasional nibble is another way sheep control internal parasites naturally. Or maybe a nibble a day keeps the doctor away.

Anyhow, I don’t think old Socrates was very smart. If he wanted to die, why not choose a more pleasant way… like maybe a big overdose  of walnut hulls and vodka.


There is a lot of debate about the toxicity of comfrey as animal feed. I think a lot of the problem is in the amount – kind of like the old adage that ‘what doesn’t kill you makes you stronger’. I have used it as chicken fodder and they appear to be just fine. Of course, they get lots of other things too so the ‘dose’ may not be too bad.

I found a blog called The Radicle Review (Notes from the Underground) which had posted an article called (Don’t) Pick Your Poison, which was written on 6/5/2010 by a lady who said she was a “certified clinical herbalist”. She was in Washington state. We don’t have certified clinical herbalists in Ohio that I know of.

She differentiated between poison hemlock (Conium maculatum), which she said was less toxic than water hemlock (Cicuta douglassi), which she described as the most toxic plant in North America. She said a quarter inch piece of the root (most toxic part of plant) would be fatal. It’s the internet, so I’d take it with a grain of salt, but not with any water hemlock. I don’t think Socrates’ suicide was his idea.

Another great item Gene.

You, of course, are dead right about what animals will and will not eat if given the chance and choice. I have spent many hours (and not one of them wasted!!) quietly watching what cattle, sheep, goats, etc will eat in fresh pasture that also contains numerous “weeds” and wildflowers. It is astonishing just how selective they are in both the species chosen and the amounts they eat. They certainly do self-medicate themselves and they also teach their off-spring to do the same. By creating pastures of just rye, clover and suchlike it is just the same as if we were force fed on a diet of only sirloin steak and ice cream – great for a while but you might as well go to McDonald’s for all the good it does you! Give animals the ability and right to choose their own foods and they will repay us handsomely with not only premium produce and off-spring but also with the good health of the animal itself.

When will we ever learn?

To the best of my knowledge, I never heard of or saw a poison hemlock plant on our farm or anyone else’s when I was growing up. I was on our local FFA agronomy judging team and do not remember ever identifying it. ( doesn’t mean I didn’t – just means I don’t remember ) The farm where we now live is about 15 miles north of where I grew up. When we first moved here in the early 70’s, the whole farm seemed to be infested with this huge fast growing weed with white flowerlets that I had never seen before. I remember asking a few people but nobody seemed to know exactly what it was. The pasture beside our lane was so thick with it that I could turn the dairy herd – 25+ cows – into that pasture and literally not be able to see a single cow. I thought anything that grew that rapidly might make good forage but the cows never seemed to eat it. They would also never eat the stalks that ended up in hay bales. I never had any unusual health problems with the cows that would have made me suspicious about its effects. It wasn’t till years after I got out of dairying that I learned that it was poison hemlock. I’m glad I didn’t know back when I was dairying – I might have worried. There is a lot to be said for stupid and lucky.

Hey, what black locust disease? I’ve never heard of that before, and didn’t find anything about it online either. I know about black locust borer; did the borer become a severe problem at some point?

Black locust rocks. I plant some every year. If there’s another problem besides the borers, I’d better find out about it. 😦

Kurt, I’m not sure what you mean by water hemlock. These names may be the problem. What I am familiar with is Conium maculatum, which the literature refers to as poison hemlock. It is very poisonous as you say. But from what I can find out, one needs to eat about six leaves of this ferny plant to die and I am not sure if that means a frond of the fern, or a little bitty segment of fern. I really truly did taste the stuff and it didn’t hurt me. Conium maculatum has been used traditionally, the books say, for medicine, but it was very dangerous to do so since the amount between being safe and unsafe was a very fine line. I had always thought Socrates committed suicide with conium maculatum, but what I read lately is that he was put to death with it. Since some historical sources think that Socrates was a fiction of Plato’s imagination, I don’t know what to think. The older I get, the less I believe. Gene

Black Walnut is not just toxic to animals. It puts out enzymes in the soil that only certain weeds can tolerate. Food crops will not grow below the drip line of a black walnut. I had to cut down one in the middle of my front yard. I made the mistake of cutting it up with a chainsaw while wearing nothing but shorts and sneakers. In about a half hour my legs were burning like crazy. I suffered 2nd degree chemical burns on my shins for three weeks and it took five weeks for the scarring to go away.

I have many medicinal herb plants that grow naturally around my property. Sheep sorrel among them. It and burdock are two of the main ingredient in the Essiac cancer treatment, which has been known to be effective even in cases up to stage four. It is also toxic in large doses just like many other herbs. We eat this delicious, tangy, lemony herb is salads when it’s available. You would have to eat more than a pound of it at one sitting to get diarrhea. You’d probably have to eat four pounds of it to kill you.

It’s all about common sense and moderation.


    I don’t mean to be condescending, but perhaps operating a chainsaw in shorts and sneakers is unwise, regardless of the tree species! I can say from experience that the cost of protective gear is trivial when considering what a chainsaw can do to your leg.


My fellow Suffolk horseowner and neighbor in Kentucky lost two young geldings when a red maple blew down in their pasture in the middle of the night and they stuffed themselves on the sweet leaves. Dropped like stones at the vet hospital despite all sorts of radical attempts to save them. In the quantities they ate, red maple leaves are very toxic. Their pasture was eaten down to bare earth in places. I would never bring this up to him as the experience was very painful, but I doubt they would have gorged themselves to lethal levels if they’d had plentiful forage to consume along with the leaves, or instead of them. And I hope I’m right as my pastures are ringed by many red maples, too.

Your ideas make good sense to me. There is, however, the matter of water hemlock which we have here. It is about the earliest thing to green up in little boggy spots. If you even licked it, you might be a dead contrary farmer. I’d suggest you check this out and make a caveat to your article.

The vet has said her blood sugar was low…and Pine needles contain glucose and sucrose…so while we were wondering why this silly cow was ingesting an abortifacient she was very precisely self-medicating.

Our dear friend’s newly acquired jersey is ill. Yesterday she was completely off her feed…he took her for a walk, and she began eating pine needles…which I had read is an abortifacient in ruminants. But there she was,5 months pregnant,eating the one thing she showed interest in…we figured she knew what she was doing…today she’s looking better, and had mosied on over to moss, clumps of sod…and our hay.

Great post Gene, and I completely concur. Before I was smart enough to know that horses and walnut don’t mix, we had a walnut tree in our barnyard. The horses always left it alone until one day when they ate all the bark off. Both seemed to be just fine afterwards.

I’ve used black walnut to good effect when worming a calf of ours that had tapeworms. Just ground up some husks in the blender and squirted it in her mouth.

Your comments about poisonous hemlocks shook loose the cobwebs of formal education. I recalled my botany professor, Charles Corbett Laing, showing us the hemlock tree, and saying this was not the hemlock which Socrates used. Dr. Laing said water hemlock was used. So I googled Socrates hemlock, and one of the sites discussed the vagaries of nomenclature and suggested that indeed water hemlock might have been used. Only judgement I could make is both were off my list of possible recreational drugs. I did google walnut hull tincture, and you are correct as usual. It’s used as a cure for worms. OK, here is something that always amazes me: how does someone discover such a thing? How many people died from hemlock before they found alcohol and walnut hulls? How much alcohol needed to be consumed before the idea of putting walnut hulls in the alcohol popped up?

There’s no question that toxicity is dose related. I can think of dozens of high-powered medicines that are helpful to patients in small doses and lethal if you give too much. Even something as innocuous as aspirin can kill if you swallow the whole bottle. But I suspect one of the reasons scientists panic about “toxicity” is that all too often they are operating in the confines of a lab instead of the real world. And believe me, that tends to both narrow and distort your vision. An animal that isn’t starving (or maybe really stupid, but generally the really stupid ones get weeded out through the process of natural selection; eating poison is sort of contra-survival!) isn’t going to eat enough of something that’s bad for them. I see the same sort of distorted thinking about germs. People try to make their environment sterile with wipes and sprays and cleansers which expose them to chemicals, instead of recognizing the world has germs, and that’s the normal condition. People have evolved to handle most germs; if you’re worried about it, focus on building up your immune system instead of sterilizing your kitchen counters!

Gene, thanks for bringing a note of sanity to the issue.

We had a doe abort a month early on her first kidding last year. We had been peeling cedar posts in preparation for splitting, charring, and planting as fence posts, and the bark was all over the goat pasture. Most of them ignored it, but Maya — the one who lost her kids — seemed to love it.

She’s pregnant again, and we’re keeping her away from cedar, but when we go on walks, she looks so longingly at it as we shoo her away.

I guess my point is that most animals know what’s good or bad for them, but a few do not. Just like people.

Hi Gene

I agree….for the most part animals are much more tolerant of poisonous plants than the ag-extension publications would have you think. My sheep routinely munched on milkweed, locust, oak leaves, maple leaves, etc. The only plant I’ve ever been religious about eradicating is Jimsonweed..mostly because it’s ugly, stinky and extremely toxic. I’ve also never had a problem with fertility, despite fields full of red clover.

What I am careful of are allowing my dogs to eat things like onions, asparagus, avocado, and grapes. I have a friend who lost a terrier to liver failure because his favorite thing was to eat grapes off the vines. You’d think an animal that can eat the nastiest, ripest roadkill, chunks of sheep manure, and dog food ought not to be susceptible to plant poisons, but I guess they are.

At this point, I’m so happy to see anything green that even the toxic plants are cheering!


Love this post. You make a good point, that some animals might be eating stuff they would not normally eat had they been given a better option.

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