Forage Poisoning in Horses

Botulism

Botulism is a serious paralytic illness caused by the toxin, botulin. It is normally associated with the ingestion of spoiled food while grazing, and is commonly called forage poisoning or clostridial disease. It takes about four to five days after eating the spoiled forage for symptoms to appear, but once they begin symptoms such as muscle failure or eating, breathing and swallowing difficulties are recognizable.

Horses are the most sensitive of the domesticated animals to be affected by botulism, and if left untreated, the disease can be fatal.

Symptoms and Types

The signs for botulism commonly include:

• Muscle failure
• Difficulty eating
• Difficulty swallowing
• Difficulty breathing
• Food and saliva in the nose
• Trouble walking
• Head low to the ground

There are seven distinct forms of botulism: designated types A through G. Those associated with horses include:

• Type A: This form has been seen in several horse outbreaks in the northwestern United States (Washington, Idaho, Montana, Oregon)
• Type B: Predominately referred to as forage botulism because of its association with contaminated forage
• Type C: Known as carrion botulism because of the association with the ingestion of feed containing a decomposing carcass (e.g., rodent, cat, dog, bird) or from eating the bones of dead animals

Causes

Botulism occurs when a horse eats spoiled forage, or forage which contains the toxin botulin. This toxin is produced by the bacteria Clostridium botulinum and can be found in grass and silage (or livestock feed such as hay) .

Diagnosis

Only your veterinarian can diagnose botulism, and it is important for the horse to be seen as early as possible after contamination for any chance of survival. Usually, botulism is confirmed through a number of tests including fecal or stomach content assessments and a complete behavioral history of the horse.