Atypical pasture myopathy – sudden death

This rapidly progressing muscle disease, also known as grass disease, has only been known since the beginning of the last century and is feared by horse owners because most of the horses affected die from it and the causes were unclear for a long time. It primarily affects young, well-fed horses that graze on rather unkempt, nutrient-poor pastures.

INHALT
Causes What happens in the horse's body after ingesting the poison? How does the disease manifest itself? Therapy Prevention is possible
Causes

After extensive research and many hypotheses, it was discovered in 2012 that a protein found in the seeds of the mountain maple tree causes this slow poisoning. However, further studies also showed that not all horses with elevated blood concentrations of the toxin become ill. It is believed that these horses are resistant to the toxin. In summer, when the horses find enough grass in the pastures, or in winter after several days of frost or snow, no cases of poisoning occur. Why this is so remains unclear.

What happens in the horse's body after ingesting the poison?

After ingesting the semen, it takes about 12 to 48 hours for the poison to take effect in the body. The protein contained in the semen inhibits certain enzymes involved in fat metabolism, causing the entire energy supply to the muscles, including the heart and respiratory muscles, to collapse.

How does the disease manifest itself?

As soon as the fat metabolism is disrupted, the horses suddenly begin to show colic-like symptoms such as pale mucous membranes, labored breathing, increased heart rate, sweating, and muscle tremors. The lack of energy in the muscles leads to a staggering gait. Muscle strength continues to decline until the animals eventually fall and, as the disease progresses, become completely immobile.

A typical behavior pattern for the disease is that affected animals still want to eat even when lying on their side and with limited chewing muscles. The body temperature drops and the breakdown and excretion of the muscle protein myoglobin causes a dark discoloration of the urine.

Horse lying in a pasture
Rolling horse
Therapy

Atypical pasture myopathy should always be treated as an emergency and treatment must be initiated by a veterinarian as soon as possible. Since there is no way to neutralize the poison that has been ingested, only the symptoms of the disease can be treated until the poison is broken down by the body. The earlier treatment is started, the better the chances of recovery for the affected horse. Medication is administered to stabilize the metabolism, muscles, and energy supply. Depending on the extent of organ and tissue damage, partial or even complete recovery may be possible. However, animals that are already lying down with severe breathing difficulties and a high pulse rate usually cannot be saved.

Prevention is possible

What can we as horse owners do to prevent the outbreak of this dreaded disease? Since the seeds and seedlings of the mountain maple can only be found in paddocks in autumn and spring, particular caution is required during this period. Ideally, grazing should be avoided during this period. Of course, this is not always possible or desirable, so it is recommended that the feed be supplemented with roughage and mineral feed during this period to prevent the seeds from being eaten due to a lack of grass on overgrazed paddocks.

As there is a suspicion that the water is also contaminated, fresh water troughs should be provided on the pastures and natural sources should be fenced off. Do not allow your horses to graze on contaminated areas for more than six hours a day during this time of year and ensure good pasture management with adequate fertilization, especially in damp areas. Completely grazed areas near maple trees should be avoided altogether.