Slobbers, otherwise known as slaframine poisoning or salivary syndrome, is a condition that causes excessive salivation or drooling in horses. It is relatively rare and usually occurs in outbreaks, with multiple horses affected at once.

Slaframine intoxication is caused by horses consuming a fungus that grows on legume forages under wet and humid conditions. Horses who ingest infected pasture, hay or silage can develop clinical signs, including hypersalivation and difficulty swallowing.

While many animals are affected by this fungus, horses are particularly sensitive. Outbreaks of slobbers have occurred in humid climates, including North America, Europe and South America. [6]

Slobbers is non-life threatening, but the drool hanging from an affected horse’s mouth is unsightly and can be a nuisance.

If you suspect your horse has slobbers, consult a veterinarian to rule out other conditions that could cause excessive salivation, such as viruses or botulism.

Signs of slobbers in Horses

Symptoms of slobbers usually develop 2-6 hours after consuming contaminated forages. [9][10] In most cases, excessive salivation is the only apparent symptom. [3]

Slobbers usually affects multiple horses on the same feed or in the same pasture simultaneously. Individual horses may show mild to severe symptoms.

The most common clinical signs of slobbers include: [5][9]:

  • Substantial amounts of saliva dripping out of the mouth
  • Constant movement of the tongue
  • Difficulty swallowing
  • Teary eyes and discharge
  • Respiratory distress
  • Diarrhea
  • Frequent urination
  • Dehydration
  • Choke

In most cases, symptoms are mild and resolve within 24 – 48 hours of contaminated forage being removed. Monitor your horse regularly for any new behaviours or worsening symptoms.

If your horse develops a fever, has an elevated heart rate or has difficulty eating and drinking, contact your veterinarian immediately.

In extremely rare cases of long-term exposure to high doses of slaframine, abortion and death have been reported. [1]

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What Causes Slobbers in Horses?

Slobbers is caused by ingestion of forages containing slaframine – a toxic alkaloid compound produced by the fungus Slafractonia leguminicola (formerly known as Rhizoctonia leguminicola).

S. leguminicola causes a disease in forages known as Blackpatch, which produces black lesions on plants. This fungus spreads across crops in wet and humid conditions.


Slaframine, colloquially known as the slobber factor, is a mycotoxin and irritant produced by S. leguminicola.

While many mycotoxins pose a serious risk to horses, slaframine is rarely dangerous if consumed for short periods of time. It can be found in various feedstuffs, including fresh and stored legume forages.

Following ingestion by the horse, slaframine is broken down in the liver and converted into its active form, 6-ketoimine. This compound mimics the neurotransmitter acetylcholine. It binds muscarinic receptors which are involved in the parasympathetic nervous system and regulate the function of exocrine glands such as the salivary glands. [3][6]

Within hours of consumption, slaframine stimulates the horse’s salivary glands, causing excessive production of saliva.

In some cases, slaframine leads to excessive excretion of other fluids from the body (eye discharge, urination, defecation). [2]


Blackpatch is a disease in clover and other legumes caused by the S. leguminicola fungal pathogen.

S. leguminicola grows and spreads quickly through the aerial mycelium. The fungus kills the leaves and stems of plants, giving a blackened, golden, gray or burnt appearance. [6]

The blackpatch pathogen is particularly difficult to eradicate from affected crops. This fungus is resilient and survives various environmental conditions.

S. leguminicola can grow in dry areas, absorbing moisture from dew to survive. Prolonged cold temperatures can harm the fungus, but small fragments of the fungus mycelium can overwinter in the soil or legume seeds. [6]

This makes it possible for S. leguminicola to survive on infected fields for years, even in periods of low temperature and humidity.

Blackpatch outbreaks can cause serious economic loss for farmers and horse owners feeding animals with infected forages. [5] It is rare that fully grown plants are killed by blackpatch, but yields can be significantly reduced.

Susceptible Forages

While slobbers is commonly associated with red clover, this fungus can grow on any legume plant. Some grass forages cause slobbers symptoms in horses, likely due to cross-contamination from other crops in the field. [5]

Most cases of slaframine poisoning occur when horses consume second-cut legume hay infected with the S. leguminicola fungus. [5][6] However, fresh pasture can also trigger symptoms.

Clover (Trifolium species)

Blackpatch disease can be identified on many legume forages, although clover tend to be the most susceptible.

If the fungus is present when red clover (Trifolium pratense L.), white clover (Trifolium repens L.) and other legumes are harvested, it can persist in stored dry hay and affect horses when consumed. [10]

Alsike clover (Trifolium hybridum) is a common forage crop for livestock in parts of Canada. However, it should never be fed to horses as it can cause several conditions, including photosensitivity and alsike clover poisoning, which can be fatal. [7]

The following clovers can be affected by blackpatch and should be examined regularly for signs of fungus growth:

  • Red clover
  • White clover
  • Crimson clover
  • Alsike clover
  • White sweetclover

Other Forages

Outbreaks of slobbers in horses can be traced back to alfalfa hays harvested at high humidity. [6] While less common, slobbers has also been associated with the following legume forages:

  • Alfalfa (Medicago sativa)
  • Black medic (Medicago lupulina)
  • Korean lespedeza (Kummerowia stipulacea)
  • Kudzu (Pueraria lobata)
  • Soybean (Glycine max)

Blackpatch-Infected Hay

Mold can grow quickly in stored, cut hay under damp and humid conditions.

It can be difficult to identify blackpatch on legume hay as the mycelium blends into the colour and texture of the forage. [6]

The toxin can remain fairly active in stored, dry hay for around 10 months to a year. [10] It has been suggested that 5-10% of the original toxicity remains after this time. [9] Its stability and concentration can lower drastically over time in stored hay, although slaframine stability in fresh legumes is unknown. [6]

Slaframine concentrations that induce slobbers can range from 1.5 ppm to 50-100 ppm, depending on the horse’s sensitivity and hay intake. [6] Consumption of small amounts of the toxin can induce clinical symptoms in some horses.


The best way to prevent slobbers is to avoid feeding forages infected with mold or fungus. However, controlling the growth of S. leguminicola at pasture is difficult, and fungicide treatments are expensive and rarely used. [6]

Plant Disease Scouting

Fields should be scouted regularly to monitor crop performance and health. Early signs of infection can be easily overlooked at different growth stages.

Blackpatch lesions vary depending on the host forage, making this disease difficult to identify.

Red clover should be examined for lesions when leaves first emerge. These lesions may appear on the leaves or stem and be gray or tan instead of black. [6]

Farmers have been known to confuse early signs of disease, such as brown leaves, for underdeveloped flowers of the clover. [4] Leaves should be magnified for examination to identify symptoms early on, before blackpatch can spread.

Treating Seeds with Fungicides

The blackpatch pathogen can spread quickly and over long distances through seed shipments. [4] Fungicide seed treatments are available, although they have been ineffective in preventing blackpatch and subseq