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.

sSigns 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
  • Dehydration
  • Teary eyes and discharge
  • Choke

Rarely, slobbers can cause: [5][9]

  • Respiratory distress
  • Diarrhea
  • Frequent urination
  • 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

    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

    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]