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What is Hound's Tongue Poisoning?

The effects of hound’s tongue on the liver have no specific treatment. If there are signs of liver failure and your horse suffers from photosensitivity (which is the skin reacting to the sunlight- much like severe sunburn) the chances for recovery are not very good. The plant has a cumulative effect meaning that the more your horse eats the toxic plant, the more toxins build up until a certain point when fatal poisoning will occur. Careful observation of the pasture and avoiding this plant is the best line of defense for your horse.

Hound’s tongue contains pyrrolizidine alkaloids and your horse is very susceptible to the toxicity of these alkaloids which cause irreversible liver damage.

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Symptoms of Hound's Tongue Poisoning in Horses

  • Photosensitivity which is the skin’s inability to defend itself from  the sun
  • Constant moving or walking around showing
  • Distress  
  • Diarrhea due to large quantities of fluid in the abdomen
  • Jaundice within the skin and mucous membranes 
  • Head pressing
  • Excessive yawning 
  • Depression
  • Head hanging 
  • Drooling and slobbering
  • Dull hair coat 
  • Weight loss 

Types  

  • Hound’s tongue is toxic weed that is native to Europe and grows flat to the ground in its first year’s growth 
  • Year two sees the growth of a long tough stem that produces a small purple pink flower with sticky seeds 
  • When pasture has been overgrazed, houndstongue is an opportunist plant and will move in to take over
  • The name comes from the leaves that are very rough and hairy much like a dogs tongue
  • It produces a very prolific seed that ‘sticks’ to other animals which is how it spreads

Causes of Hound's Tongue Poisoning in Horses

  • Although unpalatable to your horse, if it is mixed in the hay or pellets it is readily eaten 
  • Some herbicides increase the palatability so be careful not to graze after spraying 
  • Large amounts of alkaloids in the plant that are toxic to your horse 
  • Pasture contamination with the plant gaining control 
  • Rapid development of irreversible liver damage 
  • Reduced food in an overgrazed paddock 
  • Curious foals may test new plants

Diagnosis of Hound's Tongue Poisoning in Horses

General behaviour of your horse is often the giveaway to how your horse is feeling. Sudden lack of energy, reluctance to exercise, followed by more symptoms soon developing such as diarrhea and weight loss hint to more serious conditions. In all cases when your horse is showing signs of serious affliction, calling your veterinarian to pay a visit is advisable. Giving your horse a physical examination, and by discussing the daily habit and diet of your horse, it will enable them to pinpoint what the problem has been caused by. 

If you suspect a certain plant like hound’s tongue, dig up a sample so you can show it to the veterinarian. Young horses or foals are curious and often experiment with new types of eating materials, so observing what is growing in your pasture or invading from over the fence line is imperative. Because hound’s tongue destroys liver tissue to a stage where the liver cannot recover, you are well advised to go down the prevention path rather than hope for a miracle cure once your horse has been affected.

The diagnostic process will include noting and evaluating the symptoms, observation of the areas affected by photosensitivity, and possible blood work to determine the level of effects on the liver known to be characteristic of hound’s tongue poisoning.

Treatment of Hound's Tongue Poisoning in Horses

There is no known treatment for this toxic plant poisoning; the alkaloids destroy the liver which is an irreversible effect. You may be lucky if your horse has only eaten a little of the plant, it will still affect him but not quite so severely. Your veterinarian will be able to advise with medication for pain but prevention is by far the best thing to strive for. Usually, this weed is not palatable to the horse who has quality pasture to graze on. Applying herbicides to the plant can help to eradicate it but be aware that some herbicides actually change the sugars in the plant and that makes it more palatable for your horse. 

Keeping your horse out of the pasture for the recommended time and more will help avoid any problems. Consulting a county weed coordinator may help you to find the right product to kill this nasty weed. Ongoing research is still being done on this plant and the effects it can impose on the unfortunate one who eats it. As new developments come through, the person to speak with is your veterinarian who keeps up with the latest advancements.

Recovery of Hound's Tongue Poisoning in Horses

If your horse has only had a small amount of hound’s tongue, removal from the area is vital and keeping him in a stall to protect him from the sun’s rays may help. There are cases of recovery depending on how much was eaten, and if this is the case with your horse, he may have a compromised liver and may never be able to perform fully again. 

Learn to identify the plants that grow within your pasture. Early detection of hound’s tongue is vital to stop the plant before it gets a hold. The main point is to avoid overgrazing, where bare patches of unprotected earth are open to this toxic pest. In the first year, it grows low to the ground in a rosette shape, but in the second year it produces a long stalk with prickly seeds that stick to everything which enables them to spread over great distances.