TOXICITY CLASSIFICATION AND SYMPTOMS

Many of these groups have exactly the same broad clinical signs, so being able to identify weeds becomes an important part of clinical signs.

Pyrrolizidine alkaloid (PA)

Pyrrolizidine alkaloid poisoning can be acute or chronic, with the acute form being much less common.

Acute poisoning can occur through the accidental ingestion of significant amounts of toxic plants in contaminated hay or feed, or a horse may suffer acute poisoning when environmental conditions have allowed pyrrolizidine alkaloid plants to become the dominant species in pasture.

Chronic poisoning occurs when the horse ingests small amounts of the plants over time.

Signs of acute poisoning may include:
> Food refusal
> Depression
> Jaundice (characterised by a yellow colouring of the
mucous membranes)
> Abdominal swelling
> Signs of colic
> Behavioural changes that may include nervousness
or excitability
> Death can occur in severe cases

Horses showing advanced signs of acute pyrrolizidine alkaloid poisoning rarely recover. Veterinary attention should be immediately sought if poisoning is suspected in your horse.

With chronic poisoning, signs may not appear for months or even years after the ingestion of pyrrolizidine alkaloid plants.

As loss of liver function gradually progresses, there is a corresponding progression in the severity of symptoms. When the liver is damaged to a critical point, liver failure progresses rapidly and death can occur soon after.

Signs of chronic poisoning may include:
> Food refusal
> Depression
> Increasing signs of jaundice
> Loss of condition
> Secondary photosensitisation – redness and swelling
of the skin in un-pigmented areas. (The nose, lips and
around eyes are commonly affected. The skin may
crack and weep fluid.)
> Yawning
> Head pressing – the horse may push its head against
a wall or other surface
> Incoordination
> Aimless wandering
> Death can occur in severe cases

There is no specific treatment for chronic pyrrolizidine alkaloid poisoning. Removal of the plants from the diet can slow the progression of symptoms. Horses with photosensitisation should be kept out of the sun to help the skin heal. Veterinary attention should be sought if chronic poisoning is suspected in your horse.

Tryptamine alkaloids (TA)

In most reported poisoning cases, the horse has been found dead in the paddock after no apparent ill health.

Of the few cases where owners were present, clinical signs included sudden instability, collapse and death. Another horse reared, collapsed then died and another galloped for 400m before collapsing and dying.

Of the few cases where owners were present, clinical signs included sudden instability, collapse and death. Another horse reared, collapsed then died and another
galloped for 400m before collapsing and dying.

If access to swainsonine-containing
plants is restricted when symptoms
first appear, there is a good chance
the horse could make a full recovery.

Tryptamine alkaloids (TA)

Signs of poisoning do not usually occur until after the horse has consumed plants for at least 3-4 weeks.

Signs may include:
> Depression
> Circling
> Incoordination
> Unpredictable behaviour – some horses may fall
down or rear while being ridden or otherwise handled

As the disease progresses, horses become increasingly depressed and some horses may appear to be asleep. The horse may become too weak to stand.

In severe cases, the horse may suffer convulsions followed by coma and death. 

There are no current treatment options for swainsonine poisoning. If access to swainsoninecontaining plants is restricted when symptoms first appear, there is a good chance the horse could make a full recovery. 

However, if the symptoms are not recognised and the horse continues consuming swainsonine plants, the damage to the brain may be too extensive for the horse to fully recover. Such horses are dangerous to ride or handle because of their ongoing unpredictable behaviour.

Taxine alkaloids (TAX)

Horses will not intentionally eat the unpalatable leaves or seeds. Most horse poisoning cases have occurred when clippings have been placed in horse areas.

All parts of the plant are toxic and mature leaves in Winter are reported to be the most toxic. Horses are highly susceptible to poisoning by taxine alkaloids and only small amounts need be ingested for death to occur. In many reported poisoning cases, the horse has been found dead in the paddock.

The first signs of poisoning may appear within an hour of ingesting material from a yew tree and the progression of symptoms is rapid. 

Signs may include:
> Decreased tone in the lips and tail
> Decreased blood flow – difficult to find an arterial
pulse
> Incoordination, staggering and trembling
> The horse may appear paralysed
> Breathing becomes difficult and noisy
> In the final stages, the horse will collapse and die,
either from heart failure or respiratory failure

There is no specific treatment for horses and. in most cases. death is likely to occur within 12 hours. 

Veterinary attention should be immediately sought if it is suspected that a horse has suffered yew tree poisoning and supportive care may help with survival and subsequent recovery.

Tropane alkaloids (TROP)

Horses will not usually eat the unpalatable plants. Most reported cases occur through the ingestion of contaminated hay or other feedstuffs. However, horses may eat the plants if no other forage is available.

Signs and severity of tropane alkaloid poisoning varies between cases because of the variability in the type and amount of tropane alkaloids in particular plants. 

The signs that may be seen include:
> Loss of appetite
> Depression
> Colic
> Rapid pulse and respiratory rate
> Dilated pupils
> Excessive thirst

In severe cases, death may occur within minutes, hours or days of ingesting the toxic plant material. Death can be due to respiratory paralysis, heart failure or rupture of the stomach. Veterinary attention should be sought if poisoning is suspected in a horse. 

Piperidine alkaloids (PIP)

Signs of piperidine alkaloid poisoning include:
> Muscle weakness
> Incoordination – ‘staggers’
> Slobbering
> Rapid pulse
> Dilated pupils
> Frequent urination and defecation
> A distinctive ‘mousey’ odour on the breath

In severe cases, the horse may die from respiratory failure. There is no specific treatment available for hemlock poisoning in horses, but supportive veterinary care can assist with survival and subsequent recovery.

Quinolizidine alkaloids (QUIN)

The seeds and seedpods contain the highest concentration of toxic quinolizidines, but the leaves are also toxic.  

The signs that may be seen in horses include:
> Muscle tremors
> Loss of appetite
> Incoordination
> Diarrhoea

Severely affected animals may die from respiratory failure. Veterinary attention should be sought if poisoning is suspected in a horse. Treatment and supportive care will help with recovery.

Pyridine alkaloids (PYR)

Signs of pyridine alkaloid poisoning include:
> Muscle tremors and weakness
> Excitement
> Increased breathing rate
> Incoordination
> Coma, paralysis and death in severe cases

Mildly to moderately affected animals usually make a complete recovery. Affected horses should be kept in a quiet, safe area and veterinary attention should be sought.

Horses affected by chronic cyanide
poisoning usually make a slow
recovery once access to cyanogeniccontaining plants has been removed.

Cyanogenic glycosides (CYA)

Cyanogenic glycosides can convert to the deadly toxin cyanide, also known as prussic acid.

Acute poisoning – signs develop rapidly after ingestion of the toxic plant material, with the first signs appearing within 10 minutes to an hour.

The signs that may be seen include:
> Rapid breathing (hyperventilation)
> Low blood pressure
> Mucous membranes are characteristically bright red
> Convulsions
> Coma, respiratory failure and death

In the most severe cases, it may only be a matter of minutes between the onset of symptoms and death and, in other cases, there may be 1-2 hours before death occurs.

Chronic poisoning – chronic cyanide poisoning can occur if a horse consumes small amounts of cyanogenic glycoside plants over time. It is thought that low levels of cyanide damage parts of the spinal cord and long nerves. 

The signs may include:
> Hindlimb incoordination that is more noticeable
when the horse is backed or turned
> Urinary incontinence
> Constipation
> Weight loss

The horse may develop urinary tract infections that can be severe. 

Horses affected by chronic cyanide poisoning usually make a slow recovery once access to cyanogenic glycoside plants has been removed. However, the prognosis may not be so good if hindlimb incoordination is advanced and/or serious urinary tract/kidney problems have developed.

Cardiac glycosides (CAR)

The ingestion of plant material containing cardiac glycosides can rapidly cause death in horses.

In many reported cases, the horse has been found dead in the paddock. Signs of poisoning appear soon after ingestion of toxic plant material. 

Signs may include:
> Colic
> Lethargy and weakness
> Diarrhoea
> Abnormal heart beat and weak pulse
> Cold extremities
> Sweating
> Shortness of breath
> Death from heart failure usually occurs within 12-48
hours after ingestion of the toxic plant

There is no specific treatment available for cardiac glycoside poisoning. Immediate veterinary attention is critical. Horses that survive cardiac glycoside poisoning may be left with permanent damage to the heart.

In mild cases of protoanemonin poisoning, the affected horse will usually recover within a few days. In more severe cases, veterinary attention should be sought and treatment will aid recovery.

Protoanemonin (PRO)

Only poisonous in fresh plants because the toxins have converted to the non-toxic form, anemonin, in dried plants. 

Signs of poisoning include:
> Blistering and swelling of the skin in and around the
mouth
> Diarrhoea
> Colic

In mild cases of protoanemonin poisoning, the affected horse will usually recover within a few days. In more severe cases, veterinary attention should be sought and treatment will aid recovery.

Steroidal saponins (STE)

The toxins reportedly cause liver disease with  secondary photosensitisation in horses.

The signs that may be seen include:
> Weight loss
> Feed refusal
> Photosensitisation – redness and swelling of the skin
in unpigmented areas; the nose, lips and around eyes
are commonly affected; the skin may crack and weep
fluid
> Lameness associated with photosensitisation of
the skin near the coronary band has been reported to
occur in some cases
> Incoordination may develop in severe cases and
death could occur

Affected animals should be removed from the pasture that contains panic grasses and veterinary advice should be sought.

Carboxyatractyloside (CT)

The seeds and first seedling leaves are the only parts of the plants that are toxic. Signs of carboxyatractyloside poisoning will not eat the burr.

The risk for poisoning in horses is through seed contamination of processed feeds or processed supplements, contamination of hay (although horses will usually selectively leave the burrs) or through the ingestion of seedlings. 

Usually unpalatable to horses, however they may be eaten if other forage is scarce. 

The signs that may be seen include:
> Depression
> Increased respiratory rate
> Incoordination
> Rigidity of limbs
> Neck and limb muscle contractions
> Convulsions, coma and death may occur in severe
cases

There is no known treatment. Veterinary care should be sought if poisoning is suspected. In mild cases, the horse may make a full recovery with supportive veterinary care. In cases of severe liver disease, the prognosis is poor.

Calcinogenic glycosides (CAL)

The early signs of poisoning are subtle and may go unnoticed.

As the condition progresses, the signs that may be
seen in horses include:
> Depression
> Weakness
> Weight loss
> Loss of appetite
> Irregular and rapid heartbeat
> Stilted gait progressing to lameness

A horse may lie down for prolonged periods. In severe cases, death can occur from heart and lung complications.

Mildly affected horses usually recover once the source of calcinogenic glycosides has been removed from the diet. Severely affected horses rarely recover to their previous level of performance and lameness problems may be permanent. Veterinary care should be sought if calcinogenic glycoside poisoning is suspected.

Severely affected horses rarely recover to their previous level of performance and lameness problems may be permanent.

Tannic acid (TAN)

The symptoms of oak poisoning can progress rapidly and the horse may die within days of the onset of symptoms.

The signs of oak poisoning include:
> Depression
> Weakness
> Incoordination
> Dehydration
> Head pressing – the horse may push its head against
a wall or other surface
> Sweating
> Diarrhoea
> Red or brown urine
> Convulsions then coma followed by death

Veterinary attention should be sought if oak poisoning is suspected in a horse.

Soluble oxalates (SOL)

Nutritional Secondary Hyperparathyroidism or ‘Big Head’. This condition is primarily a problem in the northern areas of Australia.

Native grasses and many introduced temperate grasses are not associated with Big Head, and are safe to use as pasture species for horses. The soluble oxalates in introduced tropical grasses combine with calcium to form insoluble calcium oxalate crystals.

The formation of these crystals reduces the absorption of calcium from ingested fodder and alters the calcium to phosphorus ratio in the diet. In effect, the horse suffers a calcium deficiency. 

This deficiency causes mobilisation of bone calcium to compensate for low blood calcium levels. Over time, the bones lose so much calcium they become soft and misshapen. Some or all horses grazing the same pasture may be affected.

This deficiency causes mobilisation of bone calcium to compensate for low blood calcium levels. Over time, the bones lose so much calcium they become soft and misshapen. Some or all horses grazing the same pasture may be affected.

The soluble oxalate content of tropical grasses is highest in periods of rapid pasture growth. Signs of the condition usually develop after 6-8 months of grazing soluble oxalate pastures. Some cases have been reported to occur after only two months. 

Signs may include:
> Stiff and shortened gait
> Joint tenderness
> Loss in condition even when plenty of pasture is
available
> Swollen jawbones – the upper, lower or both
jawbones can be affected

Removal of the horse from the soluble oxalate pasture should see the resolution of lameness problems and the horse should regain condition. Facial swelling should also resolve, unless it is severe. If the swelling is severe supplements, are needed to reduce the bone swelling.

Quinones (QUI)

The toxin in St John’s Wort is highest in the plant during rapid growth in Spring through to the end of flowering. Horses grazing pastures heavily infested with St John’s Wort can develop photosensitisation within days of initial exposure.

Signs of poisoning may include:
> Redness and swelling of the skin – the nose, lips,
lower legs and the areas around the eyes are most
commonly affected; the skin may blister, crack and
weep fluid
> The horse may appear to be sensitive to light
> Lameness may occur in severe cases where skin
damage occurs on the coronet and around joints
> Some horses may appear restless
> Diarrhoea

The skin usually heals when access to St John’s Wort is restricted. The horse should be kept out of direct sunlight while the skin heals. Veterinary attention should be sought.

Lectins (LEC)

All parts of plants containing lectins are poisonous, but most cases of poisoning are associated with the ingestion of seeds, as this part of the plant contains the highest levels of toxins.

Poisoning is often the result of seed contamination of grain. The signs of poisoning can appear within hours or days after ingestion of the toxic plant material.

The signs that may be seen include:
> Loss of appetite
> Colic
> Diarrhoea – in severe cases, the diarrhoea contains
blood
> Weight loss
> Dehydration
> In cases of black locust poisoning, the horse may
have dilated pupils and develop heart irregularities

In severe cases of lectin poisoning where the horse has not received prompt treatment, death may occur through hypovolemic shock. There is no specific treatment for lectin poisoning. Veterinary attention should be sought. Horses do not often die from the ingestion of lectin-containing plants. 

The toxin in St John’s Wort is highest in the plant during rapid growth in Spring through to the end of flowering. Horses grazing pastures heavily infected with St John’s Wort can develop photosensitisation within days of initial exposure.

Propyl disulphide (PD)

Signs of poisoning include:
> Dark red-brown urine
> Pale mucous membranes
> Increased heart rate
> Staggering and partial paralysis in severe cases
> ‘Onion breath’ is a distinctive sign

Horses generally recover over the course of several weeks if the source of the propyl disulfide is removed. Abortion has been reported in pregnant mares suffering significant anaemia.

Thiaminase (THI)

Usually, the plant is unpalatable to horses. Poisoning could occur if horses are fed hay contaminated with plants containing thiaminase. 

The symptoms are progressive and appear in the
general order of :
> Rapid weight loss, even if the horse has a good
appetite
> Lethargy
> Irregular heart rate
> Incoordination when asked to walk, ‘staggers’
> Wide stance with arched back.
> The horse may appear to be ‘crouching’
> Severe tremors may develop and the horse may be
unable to rise if it falls down
> Pulse becomes fast and weak
> The horse may lie down, convulse and die

After the initial symptoms appear, the disease progresses rapidly and, without veterinary attention, the horse may die within 2-10 days.

Tannic acid (TAN)

The signs of oak poisoning include:
> Depression
> Weakness
> Incoordination
> Dehydration
> Head pressing – the horse may push its head against
a wall or other surface
> Sweating
> Diarrhoea
> Red or brown urine
> Convulsions then coma followed by death

After the initial symptoms appear, the disease progresses rapidly and, without veterinary attention, the horse may die within 2-10 days.

[Diterpene esters] are usually unpalatable to horses, but may be eaten if other pasture is scarce. Poisoning could also occur through the ingestion of contaminated hay.

Diterpene esters (DIT)

Diterpene esters are present in the sap of plants of the genus Euphorbia. The sap in euphorbias is toxic in fresh or dried plants. Most species have relatively low toxicity and cause only mild effects if ingested.

The plants are usually unpalatable to horses, but may be eaten if other pasture is scarce. Poisoning could also occur through the ingestion of contaminated hay. 

The onset of symptoms can occur within minutes of ingestion of euphorbia plant material containing high levels of diterpene esters. 

Signs may include:
> Irritation and blistering of the mouth and the skin
around the mouth
> Salivation
> Colic and diarrhoea can occur in severe cases

Topical ointments can be used to treat skin irritation. Veterinary attention should be sought, especially if symptoms are severe.

Meliatoxins (MEL)

All parts of the tree are extremely poisonous, but it is thought the fruits are most toxic.

Signs of poisoning may include:
> Diarrhoea and straining
> Colic
> Excess salivation
> Incoordination and excited behaviour
> Seizures
> Depression
> Paralysis, coma and death

Signs of poisoning usually appear within two hours of ingestion and the symptoms are progressive. Immediate veterinary attention should be sought. Once the symptoms become severe, there is little chance of recovery.

Black bean (BB)

The ripe seeds of this tree contain an unknown toxin or toxins.

Signs of poisoning that may be seen include:
> Depression
> Weight loss
> Diarrhoea that may contain blood; the faeces may
appear dark and ‘tarry’
> Laboured breathing
> Frequent urination
> Sudden death can occur in some rare cases

Veterinary attention should be sought if poisoning is
suspected in a horse.

Crofton Weed (CW)

Crofton weed poisoning in horses is known as ‘Numinbah horse sickness’ in New South Wales and ‘Tallebudgera horse disease’ in Queensland.

The symptoms of poisoning may develop after only a few weeks or after several months of grazing infested pasture.

Signs include:
> Coughing, particularly during exercise
> Exercise intolerance
> Depression
> Loss of condition
> Laboured breathing
> Respiratory failure leading to death

There is no known treatment for the condition and lung damage caused by these plants is largely permanent. 

Moderately to severely affected horses may never again be capable of strenuous exercise and may be at risk of sudden respiratory failure if forced to exercise. Veterinary attention should be sought.

Australian stringhalt (AS)

It is thought the development of Australian stringhalt may involve particular environmental factors or the growth of a soil fungus on the suspected weeds.

Australian stringhalt usually occurs in late Summer or early Autumn, and it most commonly occurs after a break in dry weather or drought conditions. Horses that graze poor quality pastures infested with a high concentration of the weeds seem to be most at risk. 

The toxin or toxins that cause stringhalt in horses are unknown. The symptoms seen with this condition are a consequence of damage to the long nerves. The symptoms usually appear abruptly and may worsen over several weeks. 

Signs of Australian stringhalt are involuntary flexion and delayed extension of the hocks. This exaggerated flexion of the hind limbs is more noticeable when backing or turning and the flexion can be so severe the front of the fetlock may strike the belly. 

Horses sometimes adopt a ‘bunny hop’ gait. Both hind limbs are usually affected and the forelimbs are occasionally affected. Wasting of the muscles can occur around the hindquarters and occasionally around the forelimbs. 

‘Roaring’ may develop if the nerves supplying the larynx are affected. Horses will usually recover if moved to paddocks that are free of flatweed and other suspected weeds. 

The recovery time varies and may take days or up to 18 months, with the average recovery time being 6-12 months. Veterinary attention should be sought if Australian stringhalt is suspected in a horse. 

Nightshades (NS)

Solanums are grown as garden ornamentals or for food (potatoes) and many species are important agricultural weeds. The closely-related tomato plant (Lycopersicon esculentum) contains toxins similar to those in plants of the Solanum genus.

The toxic effect that ingested solanum plant material will have on a horse depends on the species, the stage of growth of the plant, the part of the plant eaten and the amount of plant material consumed.  

In general, the leaves and green fruits of solanums are the most toxic parts of the plants. Most solanum plants are unpalatable, but they may be eaten if no other forage is available. Poisoning could also occur through the ingestion of contaminated hay. 

Signs of poisoning may include:
> Depression
> Drowsiness
> Dilated pupils
> Salivation
> Laboured breathing
> Incoordination
> Muscle weakness
> Involuntary urination
> Convulsions
> Paralysis
> Colic
> Diarrhoea that contain blood
> Constipation and intestinal stasis

Veterinary attention should be sought. Mild to moderately affected horses should make a full recovery with supportive veterinary care. 

In general, the leaves and green fruits of solanums are the most toxic parts of the plants. Most solanum plants are unpalatable, but they may be eaten if no other forage is available. Poisoning could also occur through the ingestion of contaminated hay.

Senna SEN

The toxins in plants of the Senna genus have not been identified. All parts of the plants are toxic, especially the seeds. The plants are unpalatable to horses and are usually avoided. Poisoning could occur through contamination of grain with senna seed or plant material.

Signs of senna poisoning include:
> Depression
> Muscle tremors
> Incoordination and swaying gait
> Shortness of breath
> Heart irregularities
> Death

Senna poisoning in horses is uncommon, but is usually fatal. Veterinary attention should be sought immediately if senna poisoning suspected.

Avocado (PER)

All parts of avocado trees are poisonous to horses, but the leaves contain the highest levels of toxins. The leaves of avocado trees are toxic even when fallen and dried. The toxin in avocado trees is called persin, but the mechanism by which it causes toxicity in animals is not known.

The signs of avocado poisoning in horses are variable
and may include:
> Non-infectious mastitis and reduced milk production
in lactating mares
> Swelling of the lips, mouth, head, neck and chest
> Colic
> Diarrhoea
> Lethargy
> Loss of appetite
> Shortness of breath and heart problems in severe
cases

Severely affected horses may die suddenly from heart failure or respiratory failure. Veterinary attention should be sought immediately.

Most horses fully recover from avocado poisoning, although milk production may not return to normal levels in lactating mares. Horses displaying signs of heart and lung damage may have ongoing complications.

Chillagoe horse disease (CRO)

Horses will readily eat these species of crotalaria and may selectively graze the plants even when other forage is available. Horses are at an increased risk of developing Chillagoe horse disease when rain produces a flush of growth in these plants.

> Signs of Chillagoe horse disease:
> Ulceration of the oesophagus
> Frequent licking of lips
> Teeth grinding
> Drooling
> Unable to swallow food or water in severe cases

Severely affected horses can die if the oesophagus becomes completely blocked. Veterinary attention should be sought. Affected horses should be removed from pastures containing crotalaria.

Chewing disease (ENE)

Prolonged ingestion can result in a disease called equine nigropallidal encephalomalacia (ENE) or ‘chewing disease’. The exact mechanism of poisoning is not completely understood.

Symptoms of poisoning in horses can occur after long periods (i.e. 1-2 months) consuming significant amounts of the plants. Horses will eat these plants if there is little alternative fodder and poisoning could occur if large amounts of the plants are consumed as contaminants of hay. 

The signs that may be seen include:
> Apparent inability to eat or drink – the horse may
have trouble getting food into the mouth; the food
often dribbles out of the mouth; the horse is able to
swallow, but is unable to get food into a position for
swallowing
> Dehydration
> Depression
> Frequent yawning and lip curling.
> Muscle tremors and incoordination are seen in some
cases

No treatment options are available for this disease at present and the damage to the brain is thought to be irreversible. Once the symptoms occur, the disease is fatal and the horse will die of starvation if not humanely euthanased.

Red clover and alsike clover (ALS)(CW)

There is some evidence the toxic effects may be caused by a mycotoxin-producing fungus that is commonly associated with these clovers. The horse seems to be the only animal species susceptible to poisoning by red clover and alsike clover.

The condition can occur at any time of year, but it seems to occur most often after an unusually long and wet Spring. The effects of the toxins are cumulative and signs of poisoning can appear within 2-4 weeks of ingesting red clover or alsike clover but, in some cases, it may be months before signs appear. 

The signs of poisoning are variable and may include:
> Photosensitisation – redness and swelling of the skin
in unpigmented areas; the nose, lips and around the
eyes are areas commonly affected; the skin may crack
and weep fluid
> Depression
> Aimless wandering
> Head pressing – the horse may push its head against
a wall or other surface
> Incoordination
> Loss of appetite
> Yawning
> Muscle tremors
> Mild colic
> Blindness
> Inability to swallow
> In severe cases, the horse may progress to episodes
of violent excitation, then coma and death

There is no specific treatment for red clover and alsike clover poisoning. Veterinary attention should be sought if red clover or alsike clover poisoning is suspected in a horse.

Mild cases will usually recover if the toxic clover is removed from the diet. Horses displaying signs of photosensitisation should be kept out of the sun to help the skin heal. Horses showing signs of advanced liver disease have little chance of survival.

Privets (PRI)

All parts of the plant are thought to be poisonous and the risk of poisoning may be highest when new growth occurs in Spring.

The signs of privet poisoning are variable and are not well documented in horses, but may include:
> Colic
> Diarrhoea
> Nasal discharge
> Incoordination
> Possible lung and heart problems – in severe cases,
sudden death from heart failure can occur

Immediate veterinary treatment should be sought if privet poisoning is suspected in a horse. Very few animals poisoned by privet have survived.

Gomphrena weed (GOM)

Gomphrena weed poisoning is uncommon as the plants are usually unpalatable and a large amount must be eaten before signs of poisoning appear.

Signs of gomphrena weed poisoning include:
> Depression
> Gait abnormalities – the horse may sway and drag its
hind feet when walking
> Difficulty turning
> Incoordination – the horse may fall and be unable to
rise
> Muscle tremors
> Convulsions followed by death

In mild cases, the horse will recover if access to gomphrena weed is removed. Veterinary attention should be sought if gomphrena weed poisoning is suspected in a horse.

Small flowered mallow (SFM)

Signs of small flowered mallow poisoning include:
> Profuse sweating
> Rapid breathing
> Incoordination – ‘staggers’
> Muscle tremors

Symptoms worsen when the horse is forced to move or is otherwise stressed Most horses recover when rested and access to small flowered mallow is restricted. 

Veterinary attention should be sought if small flowered mallow poisoning is suspected in a horse. 

Red maple (RM)

The bark and the dried or wilted leaves of red maple are known to be toxic to horses. Fresh green leaves are not toxic to horses.

Signs of red maple poisoning include:
> Feed refusal
> Weakness and depression
> Increased respiratory rate and heart rate
> Blue or purplish tinge to the skin, due to deficient
oxygen in the blood
> Jaundice (characterised by a yellow colouring of the
mucous membranes)
> Red-brown urine
> Abortion in pregnant mares
> Coma and death

Veterinary attention should be immediately sought if red maple poisoning is suspected in a horse. Horses with advanced signs of red maple poisoning have little chance of survival.

Birdsville horse disease (BHD)

The ingestion of these plants can cause poisoning in horses and such cases are said to be suffering ‘Birdsville horse disease’. Signs of poisoning appear after around 10 days of grazing the plant.

The signs include:
> Depression
> Loss of appetite
> Progressive incoordination
> Splayed stance
> Dragging of hind feet
> Head and tail elevation
> The horse may lose control of its hindquarters and
fall when stressed or when cantering
> In severe cases, the horse may lie down and death
may follow

Veterinary attention should be sought if Birdsville horse disease is suspected in a horse. An affected animal should be kept calm and should be contained in a safe area to avoid injury brought about by its incoordination. Horses showing severe signs of incoordination have little chance of survival.

Veterinary attention should be immediately sought if red maple poisoning is suspected in a horse. Horses with advanced signs of red maple poisoning have little chance of survival.

Stinging nettles (STI)

The hairs of stinging nettles can cause intense irritation on contact. The hairs contain toxins that are a mixture of histamines and amines. All stinging nettles have the potential to act as irritants.

Horses will normally avoid stinging nettles, but the risk of exposure is high in paddocks containing large infestations of the weed. 

Signs of stinging nettle poisoning include:
> Skin irritation and discomfort
> Hives may be seen around the muzzle if the plant is
accidentally contacted while grazing
> Hives can appear on any body part if the horse has
rolled in a patch of stinging nettles
> Incoordination and muscle weakness in severe cases

Symptoms of exposure to stinging nettles usually resolve within a few hours. In horses showing severe symptoms, veterinary attention should be sought. The administration of sedatives and analgesics will reduce discomfort.

Gympie stinger (GYM)

The stalks and leaves of the Gympie stinger are covered in tiny stinging hairs that contain a toxin called moiridin. If the stinging hairs penetrate the skin, the toxin causes intense pain that can last for days.

Signs of gympie stinger poisoning include:
> Initial tingling sensation developing into intense pain
> Horses have been reportedly driven to frenzy and
self destruction by the pain

There are no known options for treatment and reports in the literature suggest that affected horses have not survived the self-destructive behaviour brought on by the pain of the toxin in this plant.

Perennial ryegrass staggers (PRS)

Recent research has shown almost all perennial ryegrass that grows in Australia contains mycotoxinproducing endophyte fungi. 

Signs of perennial ryegrass staggers include:
> The horse may appear normal while grazing, but will
startle to sudden stimuli
> If handled or otherwise disturbed, the horse may
tremble and appear uncoordinated
> If the horse is asked to move the legs may splay and
hind limb flexion is exaggerated
> The horse may collapse and then get back to its feet
after a few minutes

Perennial ryegrass staggers usually resolves once access to ryegrass pasture has been removed. The risk to horses is injury caused by uncoordinated movements or a panicked response to stimuli. Veterinary attention should be sought if perennial ryegrass staggers is suspected in a horse. 

Corynetoxins (RAT)

Corynetoxins are toxins produced by the bacteria Rathayibacter toxicus. This bacterium normally lives in the soil, but it can sometimes infect the seed heads of certain grasses.

Seed heads may look normal or they may be somewhat twisted and deformed, and some may exude a yellow slime. Grasses containing corynetoxins are poisonous to all livestock species. Horses are at risk if they ingest the infected grasses, the stubble after hay has been cut, or the hay of infected grasses.

Hay cut from infected grasses can remain toxic for years. The grasses that have been known to accumulate corynetoxins in Australia are annual ryegrass, blown grass and annual beardgrass. 

Signs of corynetoxin poisoning occur abruptly and
include:
> Muscle tremors and shivering.
> Incoordination, stumbling, stiff legged gait
> Wide stance
> Convulsions and death

Affected animals should be moved to a quiet area, and should be supplied with water and good quality food. Veterinary attention should be sought immediately if corynetoxin poisoning is suspected in horses. Horses that survive corynetoxin poisoning can take up to a month to make a full recovery.

In Australia, the main risk of a horse developing ergotism is through the ingestion of paspalum that has been infected with the fungi Claviceps paspali. Such horses are said to be suffering ‘paspalum staggers’.

Paspalum staggers (PS)

Growth of fungi from the genus Claviceps on grass flower heads produces a substance known as honeydew. Honeydew is a sweet liquid that contains spores of the fungus. The honeydew is spread between grass flowers by insects.

Once the fungi have spread to new plants, the spores grow in the flower head and form an endophyte structure that is called an ergot. The ergot falls off the plant and remains in the soil over Winter. 

In the following Spring, the ergot forcibly ejects spores to infect developing grass flower heads and the cycle starts over. Horses suffering the toxic effects of ingesting ergots are said to be suffering ‘ergotism’.

In Australia, the main risk of a horse developing ergotism is through the ingestion of paspalum that has been infected with the fungi Claviceps paspali. Such horses are said to be suffering ‘paspalum staggers’. 

Paspalum staggers produces signs that are identical to
the signs of perennial ryegrass staggers which include:
> The horse may appear normal while grazing, but will
startle to sudden stimuli
> If handled or otherwise disturbed, the horse may
tremble and appear uncoordinated
> If the horse is asked to move the legs may splay and
hind limb flexion is exaggerated
> The horse may collapse and then get back to its feet
after a few minutes

Paspalum staggers usually resolves once access to paspalum pasture has been removed. The risk to horses is injury caused by uncoordinated movements or a panicked response to stimuli. 

The horse should be kept in a quiet, secure area to prevent excitement and possible injury. Veterinary attention should be sought if paspalum staggers is suspected in a horse.

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