Yes, rhubarb is toxic to dogs, cats, horses, and livestock. The ASPCA classifies rhubarb as poisonous to all three common domestic species, and the danger comes primarily from the leaves, which contain high concentrations of soluble calcium oxalates. The stalks, the part humans eat in pies and jams, contain much lower levels and are not considered a significant concern.
Why the Leaves Are Dangerous
Every part of the rhubarb plant contains oxalic acid, but the leafy blades contain far more than the stalks. Rhubarb leaves hold roughly 0.5 grams of oxalic acid per 100 grams of leaf material. When an animal eats the leaves, those soluble oxalates are absorbed into the bloodstream and bind to calcium. This pulls calcium out of circulation, potentially dropping blood calcium levels low enough to cause tremors and muscle weakness.
The bigger threat is to the kidneys. As the body tries to clear the bound calcium oxalate, crystals can form and lodge in the kidney’s tiny filtration tubes, damaging them directly. Free radicals generated during this process add to the injury. If enough tissue is damaged, the result is kidney failure, which can be life-threatening.
Which Animals Are at Risk
Dogs, cats, and horses are all susceptible. For household pets, even a moderate amount of leaf material can cause problems because of their relatively small body size. A dog that tears up a rhubarb plant in the garden and chews through the leaves is at meaningful risk, while a quick nibble of a stalk is unlikely to cause harm.
Livestock face a slightly different picture. Cattle, sheep, and goats are more likely to encounter rhubarb if it grows near pasture edges or if garden trimmings end up in a compost pile accessible to animals. The Merck Veterinary Manual notes that significant poisoning from soluble oxalate plants is more readily seen in livestock grazing large quantities, rather than taking a small taste. But because these animals may eat steadily over time rather than in one dramatic episode, chronic low-level exposure can still contribute to kidney stress.
Signs of Rhubarb Poisoning
Symptoms can show up within hours of ingestion and range from mild gastrointestinal upset to serious systemic problems. The Pet Poison Helpline lists these common signs:
- Early signs: drooling, loss of appetite, vomiting, diarrhea
- Moderate signs: lethargy, weakness, tremors
- Kidney-related signs: bloody urine, changes in thirst, increased or decreased urination
A small exposure might only produce drooling and an upset stomach. Larger ingestions, particularly of the leaves, can progress to tremors from calcium depletion and eventually signs of kidney damage. If you notice your pet producing very little urine or no urine at all after eating rhubarb, that suggests the kidneys are already compromised.
How Much Is Dangerous
There is no precise published toxic dose per kilogram for every species, which makes it hard to judge safety based on the amount eaten. In humans, the estimated lethal dose of oxalic acid is around 15 to 30 grams, which would require eating several kilograms of leaves. But smaller amounts can still cause nausea, vomiting, and kidney irritation well below that threshold.
For a 10-pound cat or a 20-pound dog, the math is much less forgiving. Their smaller body mass means a comparatively small amount of leaf material can deliver a proportionally larger dose of oxalic acid. The general rule: any ingestion beyond a tiny nibble of the leaves warrants concern, especially in cats and small dogs.
What Happens at the Vet
If your pet eats rhubarb leaves, the vet’s approach depends on how much was consumed and how recently. For anything more than a small taste, treatment typically involves inducing vomiting to get the plant material out, followed by activated charcoal to reduce further absorption. Intravenous fluids for 24 to 48 hours help flush the kidneys and protect them from crystal buildup.
Blood work will check calcium levels and kidney function markers. If kidney damage has already occurred, your pet may need extended fluid support and monitoring. The kidneys have some ability to recover from mild to moderate injury, but severe damage from heavy oxalate crystal deposits can lead to lasting kidney insufficiency. Early treatment makes a significant difference in outcome.
Keeping Animals Safe Around Rhubarb
If you grow rhubarb, the simplest precaution is fencing the patch so pets and livestock cannot access it. When you harvest stalks, bag the leaves and dispose of them rather than tossing them into a compost pile that animals can reach. This is especially important for horses and goats, who are curious foragers and will sample unfamiliar plants.
The stalks themselves are not a practical concern. Their oxalic acid content is low enough that humans eat them safely, and a dog that grabs a piece of raw stalk is unlikely to experience anything worse than mild stomach upset from the tartness. The real danger is concentrated in those large, fan-shaped leaves, and keeping animals away from them is straightforward once you know the risk.