As an equine veterinarian, one of the questions I am asked most often by garden-owning horse keepers is whether kitchen-garden plants are safe to share over the fence. Rhubarb comes up again and again, usually because it grows in abundance and the trimmings seem like a harmless treat. I want to be direct from the start: rhubarb is not safe, and the answer to “is rhubarb safe for dogs, horses, or any grazing animal” is no. In horses specifically, rhubarb is toxic, and this guide explains exactly why and what to do if exposure happens.

Is Rhubarb Safe for Horses?

No. Rhubarb is toxic to horses. Both the broad leaves and the familiar red-green stalks contain soluble calcium oxalates and oxalic acid. When a horse ingests these compounds, the oxalates bind to calcium in the bloodstream and can also form crystals that damage the kidneys. There is no portion size I would ever call safe, which is why people searching “is rhubarb bad for dogs” or horses keep landing on the same firm answer: keep it away entirely.

Horses are trickle feeders designed to eat grass and forage across many hours of the day. Their digestive systems are not equipped to neutralize concentrated plant toxins like oxalic acid the way some other species partially can. So when someone asks “is rhubarb toxic for dogs” and worries the same applies to their horse, they are right to be cautious. The toxicity principle is the same across species, and in a large grazing animal the risk is compounded by the fact that horses may eat a surprising volume of a plant once they start.

Why Rhubarb Is Dangerous for Horses

The danger comes from two related compounds. The first is soluble oxalates, which lower the amount of usable calcium in the blood, a state called hypocalcemia. The second is oxalic acid and insoluble oxalate crystals, which can lodge in and injure the kidneys. Together these mean rhubarb does not just upset the stomach, it can affect the heart, muscles, and kidneys, which are the systems that depend on stable calcium levels.

The leaves are the most concentrated source of these toxins, but the stalks are not safe either. Cooking does not destroy oxalates in any meaningful way for equine safety, so there is no preparation that makes rhubarb acceptable for a horse. This is why I never recommend feeding garden rhubarb, rhubarb peelings, or wilted rhubarb plants discarded onto a pasture or compost pile a horse can reach.

Risks and When to Avoid It

Always avoid rhubarb. There is no scenario in which I would feed it. If you are wondering “what happens if my horse eats rhubarb,” the answer depends on how much was eaten relative to the horse’s size, but signs of oxalate toxicity can include excessive drooling, reluctance to eat, abdominal discomfort or colic, muscle tremors, weakness, a staggering or unsteady gait, and changes in urination as the kidneys come under strain. In serious cases the calcium disruption can affect heart rhythm.

The highest-risk situations are gardens that back onto paddocks, hedge-line plantings within reach of a curious horse, and grass clippings or garden waste tipped into a field. Bored horses, foals, and those on sparse pasture are most likely to investigate unfamiliar plants. Treat any access to rhubarb as a reason to act, not to wait and see.

How Much Rhubarb Can Horses Eat?

None. When people ask “how much rhubarb can horses eat,” they are usually hoping for a small safe allowance, and I understand why. But there is no established safe dose, and I will not give a number that could be misread as permission. Because the toxic oxalates accumulate and the leaves are so concentrated, even a modest amount contributes to the problem. The only correct serving of rhubarb for a horse is zero.

Plenty of safe forage and treat options exist, so there is never a need to take a chance with a known toxic plant. Stick with good-quality hay, pasture grass, and vet-approved treats rather than experimenting with garden produce.

Can Foals Eat Rhubarb?

No. The answer to “can foals eat rhubarb” is an even firmer no than it is for adult horses. Foals have a much lower body weight, so a smaller quantity of oxalates reaches a toxic threshold. Their kidneys and overall systems are still developing, which makes them less able to cope with the calcium disruption that oxalates cause. A foal that nibbles rhubarb leaves can become unwell quickly.

If you keep foals or young horses, walk the perimeter of their turnout and remove any rhubarb growing within reach. Curiosity and a tendency to mouth new plants make youngsters especially likely to sample something they should not.

What To Do If Your Horse Ate Too Much Rhubarb

Treat rhubarb ingestion as an emergency, and do not wait for symptoms to appear. First, remove any remaining rhubarb so your horse cannot eat more, and take a rough note of how much was eaten and which parts, leaves or stalks. Then call your veterinarian right away. You can also reach ASPCA Animal Poison Control at 888-426-4435 for round-the-clock guidance while your vet is en route.

Do not try to induce vomiting, because horses physically cannot vomit, and do not attempt home remedies without professional direction. Your veterinarian may recommend monitoring blood calcium, supporting the kidneys with fluids, and other care based on how much was consumed. The sooner you act, the better the outcome, so make the call quickly rather than searching for reassurance that everything will be fine.

Before sharing anything from the garden or kitchen, check whether it is safe first. Here are other common items horse owners ask about:

When in doubt, leave it out, and contact your veterinarian or ASPCA Animal Poison Control at 888-426-4435 if you think your horse has eaten something toxic.