What is Ergot Alkaloid Toxicity?
Ergot alkaloids are a naturally occurring chemical compound that is most frequently found in large concentrations in the fungi in the Claviceps family. These fungi tend to infest the types of grains and cereals that horses consume, and when ingested in large enough quantities can cause tremors, loss of coordination, and in rare cases, delirium and death. The ergot alkaloids also have a cumulative effect, which means that in several smaller doses it can also have an effect, and the acute symptoms may show up after enough has been accumulated in the system, along with additional symptoms such as lameness and gangrene of the extremities. The effects of ergot alkaloids can be more severe in broodmares, particularly late in the pregnancy.
Ergot alkaloids can cause acute toxicity in equines when consumed in large amounts or chronic toxicity if consumed in moderate amounts over several days. It is particularly detrimental for pregnant mares.
Symptoms of Ergot Alkaloid Toxicity in Horses
The symptoms of ergot alkaloid toxicity can occur suddenly in the case of acute toxicity or gradually over a few days if the amount being consumed is moderate but continuous. Symptoms can include:
- Gangrene in limbs
- Loss of appetite
- Loss of coordinatio
- Poor performance
Broodmares who consume substances with ergot alkaloids are more likely to experience traditional symptoms, as well as being at risk for additional symptoms and signs such as:
- Prolonged gestation (fescue poisoning)
- Reduced or halted milk production
- Slow or difficult labor
- Thickened or retained placenta
- Uterine contractions
Ergot poisoning- The most frequent culprit that causes ergot alkaloid toxicity is the fungi in the Claviceps family. It is most often found in the form of Claviceps purpura (rye ergot fungus), which is parasitic to several types of grass and cereal, most notably rye grass.
Fescue poisoning- Fescue grass can be infected with a fungus called acremonium or neotyphodium coenephialum. Although ergot fungi are the usual source of toxicity from ergoline alkaloids, a few other plants, including the acremonium coenephialum fungus and some types of morning glory also contain this alkaloid. When eaten in large enough quantities this can cause fescue poisoning, which is very similar in behavior to ergot poisoning.
Causes of Ergot Alkaloid Toxicity in Horses
The neurotropic effect that this compound has on most mammals, which causes the tremors, loss of coordination, and delirium, was used in one of its derivatives, LSD. Ergot alkaloids also have a vasoconstricting effect on the body, meaning that the flow of blood through is restricted, or in some cases cut off entirely. Vasoconstriction that continues for several days can lead to the death of the blood-starved tissues as well as the development of gangrene. This constriction of the blood vessels is also responsible for the difficulties that are experienced by broodmares.
Diagnosis of Ergot Alkaloid Toxicity in Horses
Your veterinarian will start with a physical examination of the horse, paying close attention to the legs, tail, and ears. Gangrene is most likely to develop on these areas of the body, and the examiner may notice that the limbs are cool to the touch and there is a clear line of distinction between healthy and unhealthy tissues. Standard tests such as a biochemical profile, complete blood count, and urinalysis will help to uncover any concurrent infections or imbalances, but at this time there are no accurate tests for ergot alkaloids in the blood or tissues.
The preliminary diagnosis of ergot alkaloid toxicity is usually made on the basis of the clinical symptoms, and confirmed by analysis of the animal’s feed as well as their pasture area. The fungus that is responsible for fescue poisoning is not visible with the naked eye and will need laboratory analysis, however, the ergot fungus Claviceps purpurea is dark purple and is generally large enough to be easily visible in the seed heads of infested plants.
Treatment of Ergot Alkaloid Toxicity in Horses
The primary remedy for ergot alkaloid toxicity is the removal of the alkaloid from the patient’s environment. Any other treatments will be supportive or symptomatic as there is no antidote for toxicity caused by ergot alkaloids. If the horse appears to be in distress, IV therapy will be utilized to prevent dehydration and imbalances in the blood chemistry levels. Any areas that have developed areas of gangrene will need to be assessed and treated.
The treatment for gangrene may require sedation to keep the horse calm while the doctor debrides any dead tissue from the wound and antibiotic or antifungal medication may be required if any bacterial or fungal infections have developed. The antipsychotic and antihypertensive drugs perphenazine and reserpine may be recommended as they have been shown to reduce the adverse symptoms. Broodmares may also benefit from the administration of domperidone as it prevents the inhibition of the release of prolactin, ensuring that milk production occurs.
Recovery of Ergot Alkaloid Toxicity in Horses
There are several measures that you can take to reduce the risk of ergot alkaloid toxins causing a problem for your horses. These can include:
- Blend different types of feed
- Control grasses growing adjacent to fields
- Do not use cereal rye straw for bedding with late-gestation mares
- Keep records regarding the weight of foals and placentas at birth
- Mow grass pastures to prevent seed heads from forming
- Prevent your horse from consuming grasses alongside the road
- Regularly check fields and pastures for the presence of ergot fungi
- Regularly test feed for the presence of ergovaline
- Use only certified endophyte-free seed