Horses are particularly susceptible to a huge range of poisons – snake and spider bites; antibiotics in feeds for other species of animals; herbicides, pesticides, fungicides; bacterial, fungal and mould toxins and certain plants. Heavy metals, nitrates and nitrites are yet another source of poisons.

“Signs of poisoning are numerous and, although they differ between poisons, a number are common and frequently encountered. These include loss of appetite, incoordination of gait and lameness, depression, diarrhoea, irregular and laboured breathing, muscular twitching, discoloured urine and unusual smell of the breath and faeces, salivation, thirst, anaemia, jaundice, blindness, dilation of pupils, colic, and photosensitization expressed as oedematous swellings around the face, eyes, neck and flanks.” (Veterinary Notes for Horse Owners)


Where snake or spider bite is suspected or known, injectable Vitamin C should be used as an immediate first aid action. Always keep Sodium Ascorbate on hand which is administered by intra-muscular injection. Dosage rate for horses is 20 ml in each side of the neck as quickly as possible, with 10 ml for ponies. Herbal treatments for rehabilitation of snake and spider bites and other cases of poisoning can be most effective, especially if commenced immediately after veterinary attention.

With all suspected poisoning immediately place the horse in a safe area to keep them quiet and try to ascertain the cause so that appropriate veterinary treatment can be administered. Follow up with herbal treatment for rehabilitation.

Common Poisons

Prevention is the key to preventing serious illness and death. Avoid exposing horses to poisons which are in virtually every product used in homes and on properties. As a guide protect horses from the following poisons.

Urea contained in cattle and sheep feeds and mineral blocks which causes kidney damage to horses, which can be irreversible if not treated.

All poisons used on properties such as sheep and cattle dips, all kinds of baits, herbicides, pesticides and fungicides, should be locked securely away from horses, other animals and children.

Antibiotics in feeds for other livestock such as Monensin (aka Rumensin and Elancoban) which are particularly toxic to horses. The great difficulty with this is that livestock feeds are often processed in the same equipment and residues can contaminate feeds or batches of feed can be labelled incorrectly. There have been a number of court cases as a result of this unfortunate occurrence.

Feeds can be contaminated by bacterial toxins caused by Salmonella which causes chronic scouring, Clostridium a cause of gas colic and Botulinum which causes botulism.

Toxins are produced by mould in hay, in rye grain and in oil seeds or cereals stored with too much moisture present.

Fungal toxins can infect lupins which cause liver damage. Similarly mycotoxins can infect perennial ryegrass and paspalum grass which if grazed in excess can cause staggers. Immediate removal from the pasture followed by veterinary treatment will prevent deterioration.

Cotton seed contains a substance gosspypol which is toxic to horses as it interferes with iron absorption. Although it is partially destroyed by heat, gossypol levels in cotton seed meal are usually not known and it should not be considered as a feed safe for horses.

Arsenic is an ingredient in some widely used proprietary horse products, which is found in nano quantities in the body, but which is toxic in excess, therefore avoid this unnatural method of “conditioning” horses.

Poisoning of plants with commonly used weed killers can actually increase the risk of horses eating a plant they would normally avoid due to the rise in sugar content. Horses should be removed from pasture before it is sprayed and left off for much longer than recommended withholding periods, which is far too short, and many have residual effects outlasting lifetimes.

“The excessive use of nitrogen fertilisers can lead to high levels of nitrates in the herbage and contamination of ground water, ditches and streams through the leeching of soils. Although nitrates are only slightly toxic they can be reduced to nitrites before, or generally after consumption.” (Veterinary Notes for Horse Owners) This reference goes on to state that nitrite toxicity causes liver damage but can be treated effectively by intravenous injection of ascorbic acid (Vitamin C).

Poisonous Plants

Evolution has produced poisonous toxins in plants as a defence for that plant against insects. Some plants need to be eaten in great quantities by horses to cause detrimental effects while others will cause damage from only a small amount. Depending on the plant only some parts of it are poisonous and only at certain stages of growth.   In others the whole plant is poisonous. Or a plant may only be toxic at certain times of the season. The species to watch out for vary enormously in different regions and countries.

Peas and beans – as a general rule do not allow horses to graze pea and bean family plants or to be fed beans of any kinds.

Sorghum hay, pasture or grain should be avoided as a horse feed, while the weed sorghum Johnson grass contains similar poisonous compounds.

Bracken Fern thrives in poor soils, horses will not readily eat it unless they are forced to do so. It causes thiamine deficiency which causes staggers and other symptoms which are treatable.

There are many species of Crotalarias native to northern Australia causing poisoning known as walkabout disease which is frequently fatal. Symptoms include aimless wandering, rapid weight loss, liver disease, and head pressing. Affects are cumulative.

Common garden plants which are poisonous to horses include hydrangea, rhododendrons, azaleas, foxglove, daffodils, jonquils, snowdrops and wysteria . Common garden trees which are poisonous to horses include prunus, plums, peaches, apricots, cherries, almonds and oak trees.

Oleander is a common cultivated garden species occurring across the whole of Australia. Apparently only seven leaves are enough to kill an average sized horse. Signs of poisoning are lethargy, weakness, colic, scours, abnormal heart beat and weak pulse, cold extremities, sweating and shortness of breath.

Avocado is a popular culinary plant widely distributed.   Signs of poisoning include swelling of the lips, mouth, head, neck and chest, colic, scours, lethargy and feed refusal. Death can result from heart or respiratory failure.

Undesirable plants can often be introduced onto a clean property in hay, so it is wise to be aware of this potential problem and eradicate these plants when there are only a few of them or to prevent from taking hold in the first place. Similarly horses coming in from another area can pass viable seeds in their manure so it is a good idea to keep such horses quarantined for at least a week in yards or small paddocks which can be thoroughly cleaned.

Due to the great variety of plants which may be poisonous to horses, it is wise to become familiar with species occurring in your own environment, so that steps can be taken to eradicate them or keep horses away from them.

Spraying of poisonous chemicals should be avoided if at all possible, instead use organic and biodynamic methods of pasture management to achieve more sustainable and healthier horse paddocks and horses. There is a whole new breed of companies and brilliant individuals developing sustainable practices in the market today.

Case History – Hazchem

Rebecca Farquhar, Katrina Station, Rolleston, Qld, writes …

“After reading your newsletter about urea poisoning, I feel the need to write this letter to warn others of the potentially lethal effects from using some cattle dips. This is particularly embarrassing for us as we have kept horses and cattle all of our lives and try at all times to keep them in the best of health but we almost killed my young studbook paint mare with cattle dip due to stupidity. We have never had a tick problem before but during the prolonged drought we have had many of the common kangaroo ticks and after not being able to hand pick all of the offenders from our 20 horses, we had used up our supply of horse insecticide preparations. My husband found a small tin of cattle dip (which I use on my rose bushes for red spider mite) and carefully read all of the written instructions. There was nothing about horses, a dosage rate OR a warning. So we diluted 3.5 ml in 2 litres of water and poured the mixture onto the freshly washed mare. The following morning the ill effects of the dip were apparent as the mare swayed in pain looking at her stomach with dull eyes. We immediately called a number of vets and horse people who were unable to tell us if the dip could be the cause of the mare’s distress. With a second examination of the tin, we noticed the tiny horse icon with a cross through it on the tin’s label which was about 5 mm in size and made the assumption that she was being affected by the dip. Immediately we washed her thoroughly and then contacted a vet from afar who had experience with this type of poisoning. Our mare suffered terribly as the dip shut down her system and we could do little except watch her round the clock and give her injections of anti-colic drugs when she would go down with stomach pain, and try to keep her moving if she stayed down too long. Due to the mare’s show condition, young age, and health, she survived and is now two weeks later, back to what appears to be her normal self. I would like to warn as many people as possible so they don’t go through this same trauma of almost killing your favourite horse with kindness, as I have since heard of deaths and near deaths in up to 6 horses at a time from this same chemical in Queensland.

Of course we still have the ticks and flies and I am terrified of putting anything near this particular mare as she now has a compromised immune system and may react to relatively safe horse preparations. What natural herbal mixtures could I put on her for the pests and for ongoing overall health and where can I get them? Please help! I have to use natural products myself as I am super sensitive and it’s time to convert my horses too!”

Rebecca then phoned for a consultation and Miss Two Sox was duly treated with a herbal detoxification program and put onto a V F Natural Diet and given information on how to prepare natural, effective and safe insect repellents. After a month she reported “Her coat has improved dramatically with a natural oily glow, her eyes are very bright and she is jumping out of her skin unlike the way she was one month after the poisoning where she has a dull coat, slight swelling around the eyes, and quite poor condition with some muscle wastage. The most dramatic change in Missy now is her muscle tone and fitness and her happy disposition.”


Epidemics of Paterson’s Curse poisoning causing fatal liver damage to horses is a regular occurrence in many parts of Australia. The tragedy of this whole scenario is that this situation can be prevented.

Paterson’s Curse (Echium plantagineum) when eaten by horses on a regular basis, causes severe liver damage which can easily result in death. This situation usually occurs when there is a seasonal flush of the weed so that it chokes out grasses. Neglect of pastures and overgrazing of paddocks leads to the weed taking over. This happens in particular after a drought where the soil is compacted and unbalanced as it thrives in these conditions, unlike good pasture grasses. It can only grow from seed but that seed can remain viable in the ground for 15 years, so prevention of seeding by aggressive slashing before flowering is one strategy.

If horses are left in these kinds of paddocks with no choice but to eat the weed, for any length of time, their livers will become damaged, often to the point of fibrosis and liver failure. If horses reach the point where they are very poor, with little or no appetite, scouring and disoriented, it is too late. Other symptoms include lethargy or uncharacteristic excitability, jaundice, lack of co-ordination, colic, photosensitivity lesions especially on white socks and blazes.

If horses are removed from the offending paddocks early, and fed a VF Natural Diet, then the damage can be prevented. If horses are already suffering some degree of liver damage, which can be assessed from a complete blood profile, they need immediate treatment with herbs such as St Mary’s Thistle, to normalise liver structure and function. This organ has a remarkable ability to regenerate which is stimulated by hepatic herbs, and reversal of fibrosis has been achieved if it is not too far advanced.

Most horses that are well fed (either pasture or hard fed) will not normally eat Paterson’s Curse. Some horses may develop a predilection for the weed, but can be balanced if treated as above. If horses do ingest only a small amount of the plant, it may not cause any harm, especially if the animal is very healthy, but it is wise to get rid of this weed from areas where horses graze. Seek advice from an organic growers’ group or similar for natural ways of doing this by balancing the soil, rather than spraying with poisonous herbicides. Where the weed has taken over in large tracts of land, it is unfortunately going to be necessary to spray as part of an eradication campaign. However on small holdings where horses are kept, horses should be removed from the area before spraying and not allowed back until the area has been regenerated with good pasture which would take some considerable time. Tragic consequences result from sick horses being left in paddocks when spraying takes place. The liver already damaged by the affects of the Paterson’s curse is dealt a fatal blow from the affects of toxic herbicides. This can also be caused from drift.

All parts of Paterson’s Curse are poisonous and the affects are cumulative.

Also known as Salvation Jane and Riverina Bluebell, it occurs throughout the whole of Victoria, NSW, South Australia, most of Queensland except the far north, parts of Tasmania and the south west corner of WA.

Case History –  Dead Horse Walking

Bridget from the Central West of NSW writes …

“When my mother and I set out to purchase a horse for me, we were appalled at the condition of the horses and felt we had to rescue at least one, so that is how we came to buy Alistair. He was a three year old colt, but looked more like a yearling. He had a beautiful kind eye and even though he was skinny, it was love at first sight. We took him home, fed him up, got him gelded and broken in. The breaker commented that he ate heaps but was very thin and falling away. I made it my mission to really fatten him up, never could I have imagined that all the while I was trying to do this, he was dying inside.

In hindsight, Alistair was brought up in paddocks filled with Paterson’s Curse which he was forced to eat and subsequently acquired a taste for it. The weed diseased his liver and the pressure of breaking him in this condition caused severe stomach ulcers.

By mid-February all attempts to get his condition up had failed. I had tried every type of feed imaginable. His appetite had diminished to the point where he would look at his feed and hay and walk away. He was in very poor condition. Even after several vet visits and full blood tests, no diagnosis was made. I was advised to turn him out on pasture and give him steroids. This proved to be a costly mistake. Within three weeks he was so emaciated his mind had started to go. He was kicking and barging. His beautiful stockings and blaze were a mass of greasy heel type lesions. I knew he had only days to live if something could not be done. I rang my vets in despair and asked if maybe Alistair could have ulcers. They said it could be possible and we started him on a commercial ulcer treatment. He ate more in four days than he had in four weeks. But he only wanted straw and the stalk of the lucerne hay, but it was a start. Two months later his mind was back to normal but his condition had hardly improved, despite continuing treatment, as he would still only eat the straw and stalks.

A dear friend who has an excellent agistment centre offered to rehabilitate him for me. Her vet did a full blood test and picked up his problem. A healthy horse’s GGT count should read between 0 – 87, his was 330 ! The vet said horses can drop dead at 200. They wanted to put him down then and there, they called him “The Dead Horse Walking”, never expected him to live, let alone recover, and said it was due to Paterson’s Curse.

Alistair’s appetite and condition started to improve with the help of probiotics and doses of B group vitamins. I then contacted Victoria Ferguson and she prescribed and dispensed herbs for his liver, ulcers and immune system and recommended a specific natural diet for him. The herbs were administered twice daily as well as treating his lesions topically. He was literally hand fed small amounts of feed around the clock. The staff had shifts to feed him. He was eventually strong enough to come home.

After two months of treatment Alistair’s liver count was only slightly elevated and after four months was in the normal range. He enjoys his whole range of natural feeds and eats everything. His weight is excellent and I have started taking him out on small rides again. Alistair and I are forever indebted to my good friend and to Victoria – they were his saviours.”

Reprinted from “The Complete Horse Herbal”

© Victoria Ferguson Dip.Herb.Med. 22 May 2019