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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]
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]
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.
Prevention
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 subsequently, slobbers.
Large-scale application of a fungicide on clover foliage before the flowering period may be effective in reducing damage to crops. However, attempts to eradicate the fungus fully are often unsuccessful.
Thiram and Benomyl were studied as blackpatch disease treatment in the 1950s but were proven ineffective in the field. Other fungicides (quinolin-8-ol, captan, etc.) provide legume protection in controlled studies but lack credibility when used on crops. [6]
New fungicides have been developed since the last studies were conducted. More research is needed to determine whether the growth of R. leguminicola can be inhibited without diminishing the growth of the legumes.
Predicting Outbreaks
Crop disease forecasting can allow for efficient management of pastures and reduction of crop loss and chemical inputs while lowering the risk of slobbers outbreaks.
Blackpatch outbreaks usually occur when humidity and dampness are high. Therefore, it may be possible to predict outbreaks by collecting environmental and climatic data from different locations where the condition is prevalent. [6]
Further research is needed to develop a reliable model for predicting blackpatch and slobbers outbreaks in susceptible areas.
Diagnosis
Consult with your veterinarian if you suspect your horse has contracted slobbers to obtain an accurate diagnosis. Your veterinarian will likely check forages and pastures for evidence of fungus growth to complete the diagnosis.
Slaframine and 6-ketoimine cannot be detected in blood and urine samples taken from horses with slobbers. [8] Diagnostic testing is unreliable for this condition, so your veterinarian will rely on the presence of clinical signs to make a diagnosis.
Physical Examination
Slobbers is straightforward to diagnose if acute, excessive salivation is present and the fungus Rhizoctonia leguminicola can be identified in contaminated forages or hays. [3]
While several conditions can cause excessive salivation, a diagnosis of slobbers can be confirmed if symptoms resolve quickly after removing contaminated feeds.
Differential Diagnosis
Before diagnosing a horse with slobbers, your veterinarians will conduct a differential diagnosis to rule out other disorders that may be causing symptoms.
Many conditions can cause excessive salivation and difficulty swallowing in horses, including: [8][9]
- Botulism
- Vesicular Stomatitis
- Rabies
- Mucosal damage
- Oral trauma or dental problems
- Encephalitis
- Pharyngitis
Treatment
The most effective treatment for slobbers is to remove the horse from the forage that triggered the condition. [11] Remove or destroy fungus-infected hays on your premises to prevent further slaframine intoxication.
Recovery is usually rapid, with symptoms often resolving within 24 – 48 hours of removal from infected forages. Horses that have consumed large amounts of slaframine or horses that are more sensitive to the compound may take longer to recover. [3]
Additional treatment is rarely needed, and lasting effects are uncommon.
Water & Electrolytes
Ensure your horse has adequate access to water when recovering from slobbers to prevent dehydration from fluid loss. If your horse has been drooling for several days, feed salt to promote water intake.
Electrolyte supplements can help prevent dehydration and aid recovery in horses affected by slobbers.
Atropine
In rare cases, your veterinarian may recommend medication to address excessive salivation. Slobbers can be controlled and partially reversed by administering the prescription-drug, atropine. [1]
Atropine prevents slaframine derivatives from binding muscarinic receptors and inducing excessive salivation. It must be administered shortly after consumption of infected feeds to prevent hypersalivation.
Atropine should be used with caution and under the supervision of a veterinarian. Sudden, significant loss of saliva can lead to transient metabolic alkalosis or accumulation of bicarbonate in the blood.
This can disrupt the delicate acid-base blood balance in the horse, causing serious illness. [8] Gastrointestinal side effects may occur. [3]
Prognosis
The prognosis for horses with slobbers syndrome is very good. Most horses fully recover within 24 hours of restricting access to infected forages.
Transitioning your horse to a different forage and providing plenty of fresh, clean water during recovery is usually the only treatment required.
References
- Arnold, M. & Smith, S. R. Slaframine Toxicosis or “Slobbers” in Cattle and Horses. University of Kentucky, Agriculture and Natural Resources Publications. 2015.
- Barnes, R. F. et al. Forages, Volume II: The Science of Grassland Agriculture. Iowa State University Press. 1995.
- Fonteque, J. H. et al. Slaframine intoxication in horse in Santa Catarina State. Arq Bras Med Vet Zootec. 2015.
- Gough, F. J. & Elliott, E. S. Blackpatch of red clover and other legumes caused by Rhizoctonia leguminicola sp. nov.. West Virginia University Agricultural Experiment Station Bulletin. 1956.
- Hagler, W. M. & Behlow, R. F. Salivary Syndrome in Horses: Identification of Slaframine in Red Clover Hay. Appl Environ Microbiol. 1981.
- Kagan, I. A. Blackpatch of Clover, Cause of slobbers Syndrome: A Review of the Disease and the Pathogen, Rhizoctonia leguminicola. Front Vet Sci. 2016.
- Nation, P. N. Alsike clover poisoning: A review. Can Vet J. 1989.
- Poppenga, R. H. Clinical Commentary: Slaframine Intoxication. Equine Veterinary Education. 2012.
- Riet-Correa, F. et al. Mycotoxicoses of ruminants and horses. J Vet Diagn. 2013.
- Wright, B. Slobbers or Slaframine Poisoning in Horses. Ontario Ministry of Agriculture, Food and Rural Affairs. 2004.
- Smith, G.W. Slaframine. Chapter 73 in Veterinary Toxicology. 2018.
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