Chemical toxins produced by mould fungi which may contaminate horse feed. The symptoms and severity of intoxication vary widely according to the mould and mycotoxin involved and the dose ingested. The following is a list of some of the known mycotoxins and their effects, but it is by no means exhaustive.

Aflatoxin from Aspergillus species of mould. Several types – B1 being the most important in horses. Found in cereals, especially corn (Mouldy Corn Poisoning) also palm- kernel meal, copra, brewing by products and peanut hulls as well as hay. May contaminate feed bins and buckets. Wide range of symptoms from sudden death to mild signs of unthriftiness, liver damage, loss of condition, reduced fertility, immune suppression, lung damage & C.O.P.D. An Irish study indicated 60% of horses investigated for poor performance showed evidence of exposure to aflatoxin antigen. Moisture and humid weather favor growth of the Aspergillus fungi and toxin production.

Ergovaline & Ergotamine. From Claviceps fungus. See Ergot Toxins & Ergotism

Lolitrems & Paspalinine. From an endophyte Fungus on Perennial Ryegrass. Causes Ryegrass Staggers, especially when pasture is heavily grazed as toxins accumulate near the base of the grass. Neurological symptoms include fine tremor, abnormal gait, staggering, neck arching, occasionally aggression or seizures. Symptoms may subside if horses are left undisturbed. No specific treatment – remove from suspect pasture.

Slaframine. Produced by a Rhizoctonia fungus affecting white clover and other legumes including Lucerne and Lupin. Causes ‘’Slobbers’’ with symptom being drooling, tearing and uncontrolled diarrhoea and urination which may last for hours or days. Treatment is supportive, plenty of water and removal from suspect pasture or removal of suspect hay.

Fumonisin. From Fusarium fungi affecting maize. Horses are especially sensitive. Toxin causes Equine Leucoenchepalomalacia (ELEM) which involves destruction of white matter in the brain. Symptoms include liver damage, depression, circling, tremors, poor coordination, loss of swallowing reflex, blindness, coma, and death.  No treatment is effective once neurological signa become apparent.

Stachyobotryotoxins from mouldy straw can cause redness and swelling of the lips and mouth with ulceration of oral mucosa, ulcers in the stomach and oesophagus and swelling of associated lymph nodes. Diarrhoea and contact dermatitis may feature.

Other known mycotoxins include Ochratoxin, Trichothecenes (DON) and Zearalenone but information on their effect on horses is limited. Where mycotoxicosis is suspected the horse should be removed from the suspect source of the mould toxin and veterinary advice sought.

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