There are many plants that can be toxic to horses, so it is important to know what is growing in and around your paddocks.
The list of potentially toxic plants is far too long to include in one article, but below are some common plants, grasses and foods that horse owners should be aware of.
It is also important to remember that toxicity can depend on the plant, the amount consumed, the part of the plant eaten and the conditions in which it is growing.
Many garden plants and fruit trees can also be toxic to horses. For this reason, avoid throwing garden prunings, lawn clippings or other garden waste into paddocks. What looks like harmless garden waste may contain plants that are poisonous to horses.
Grass Clippings
Grass clippings from mowing should never be fed to horses.
The small particle size can increase the risk of choke, while the clippings can also begin to ferment rapidly. This can contribute to digestive disturbances, colic and other potentially serious problems.
Grass clippings may also contain plants or chemicals that are unsuitable for horses, making them best kept out of the paddock altogether.
Avocado
Avocado plants contain persin, a toxin that can cause serious illness in horses and other animals.
Avoid allowing horses access to avocado trees, leaves, fruit, branches or other parts of the plant.
Bracken Fern
Bracken fern can cause poisoning when horses consume it over an extended period.
Signs can include weakness, incoordination and an unsteady or staggering gait. Toxicity can develop after horses have eaten bracken repeatedly over several weeks or months.
If bracken is growing in your paddocks, it is best to remove it and prevent horses from accessing it.
Cruciferous Vegetables
Broccoli, cabbage, cauliflower and Brussels sprouts can cause digestive problems and excessive gas when consumed in large amounts.
They are best avoided as horse feed rather than being offered as a regular treat.
Peach, Cherry, Plum and Apricot Trees
The leaves, twigs and bark of peach, cherry, plum and apricot trees can be toxic to horses.
The fruit itself is not considered toxic in the same way, but large quantities of fruit should not be fed as they can cause digestive upset and potentially contribute to colic.
Keep horses away from these trees, particularly if branches have been damaged or fallen into the paddock.
Onion
Onions can damage red blood cells and may cause anaemia when consumed in sufficient quantities.
Avoid feeding onions or allowing horses access to large quantities of onion waste.
Nightshade Family
The nightshade family contains a number of plants that can be toxic to horses.
This family includes potatoes, tomatoes, eggplant, capsicum and chilli, along with a range of wild plants and herbs.
Because toxicity varies between species and plant parts, it is safest to prevent horses from consuming nightshade plants growing in or around their paddocks.
Perennial and Annual Ryegrass
Perennial and annual ryegrass can harbour microscopic fungi known as endophytes.
Some endophytes produce mycotoxins that can cause problems in horses. Ryegrass-associated toxicity can cause ryegrass staggers, with signs including trembling, incoordination, an unsteady gait and difficulty controlling movement, particularly through the hindquarters.
The risk can vary depending on the particular ryegrass and the endophyte it contains.
For more information, see our articles on problematic pasture grasses and horse pasture and mineral balance.
Johnson Grass
Johnson grass (Sorghum halepense) can cause cyanide poisoning under certain conditions.
Signs can develop rapidly and may include rapid breathing, tremors, frequent urination and defecation, gasping and convulsions.
Sorghum species can become particularly hazardous under certain growing and environmental conditions, so horses should not be allowed access to suspect plants.
Hemlock
Hemlock (Conium maculatum) is highly toxic.
Signs can appear relatively quickly after consumption and may include nervousness, tremors and incoordination, followed by depression, reduced heart and respiratory rates and potentially colic.
Severe poisoning can result in respiratory failure and death.
Ragwort
Ragwort contains pyrrolizidine alkaloids, which cause cumulative liver damage.
One of the dangers of ragwort poisoning is that there may be little obvious evidence that the horse has been eating it until significant liver damage has occurred.
Signs can include photosensitisation, reduced appetite and weight loss, progressing to depression, incoordination and jaundice.
Ragwort remains toxic when dried and can therefore be particularly concerning if it contaminates hay.
Paterson's Curse / Salvation Jane
Paterson's curse (Echium plantagineum), also known as Salvation Jane, contains pyrrolizidine alkaloids that can cause cumulative liver damage.
Horses are particularly susceptible, and poisoning can eventually result in loss of condition and death.
It is important to remove Paterson's curse from areas where horses graze and to take care that it does not contaminate hay.
Fireweed
Fireweed (Senecio madagascariensis) contains pyrrolizidine alkaloids and can cause irreversible liver damage when consumed over time.
Fireweed is particularly important to be aware of in Queensland and other parts of Australia. Poisoning is more likely when other feed is limited, when plants are young and difficult to distinguish from pasture, or when contaminated hay is consumed.
Heliotrope
Heliotrope (Heliotropium species) contains pyrrolizidine alkaloids that can cause cumulative liver damage.
It may become more prevalent after summer rain, particularly where there is bare or degraded ground.
Because horses may consume toxic plants when there is insufficient alternative forage, maintaining good pasture cover and providing adequate hay are important parts of prevention.
Flatweed
Flatweed can be associated with stringhalt, a neurological condition characterised by exaggerated flexion of one or both hind legs.
It is particularly associated with autumn conditions and can become a problem following drought.
St John's Wort
St John's wort (Hypericum perforatum) can cause photosensitisation in horses and other grazing animals.
Affected areas of skin become extremely sensitive to sunlight, potentially causing severe irritation and damage.
St John's wort is one of the poisonous weeds identified as a concern for horses in Australia.
Other Plants to Be Aware Of
There are many other potentially toxic plants that may occur in Australian pastures, paddocks and surrounding areas.
These include:
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Foxglove (Digitalis purpurea)
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Oak trees
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Paterson's curse / Salvation Jane (Echium plantagineum)
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Red maple (Acer rubrum)
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Capeweed
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Common heliotrope (Heliotropium europaeum)
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Cotton bushes
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Black walnut (Juglans nigra)
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St John's wort (Hypericum perforatum)
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Castor bean plant (Ricinus communis)
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Mistletoe (Viscum species and other mistletoes)
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Milkweed (Asclepias species)
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Phalaris / canary grasses (Phalaris species)
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Rattlepods (Crotalaria species)
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Pimelea species
Some of these plants are more significant in particular parts of Australia, while others become more hazardous under particular environmental conditions.
Don't Forget Toxic Plants in Hay
Toxic plants aren't only a paddock problem.
Some plants remain toxic after they have been dried and can therefore end up in hay. This is particularly important with plants such as ragwort and other pyrrolizidine-alkaloid-containing weeds.
Always check hay carefully and avoid feeding hay that is contaminated with known toxic plants.
Know What Is Growing in Your Paddocks
The best way to protect your horse is to know what is growing in and around their grazing areas.
Walk your paddocks regularly and learn to identify unfamiliar plants before allowing horses access to them. Be particularly vigilant after rain, drought or changes in pasture conditions, as these can encourage the growth of weeds and other plants that may present a risk.
Good pasture management, adequate forage and preventing access to known toxic plants can all help reduce the risk of plant poisoning.
If you suspect your horse has eaten a potentially toxic plant or is showing signs of poisoning, seek urgent veterinary advice.
For more advice, complete our complimentary Horse Questionnaire.