Recent research into sycamore seeds, which can cause atypical myopathy when consumed by a horse and is a serious threat — potentially fatal — to equine health, has found that levels of toxicity (hypoglycin A) increase when the seedlings are ground up and eaten.
The research was disclosed by Professor Richard Piercy, Professor of Comparative Neuromuscular Disease at the Royal Veterinary College, at the National Equine Forum.
“If you take sycamore seeds, grind them up in a pestle and mortar and then store them in different ways, the amount of hypoglycin A will go up,” he said.
“If you add some water and store them at room temperature, the amount of hypoglycin A is much higher than if the tissues are stored at lower temperatures.
“What’s interesting is that if you just have the whole seeds and store them in the same ways, we don’t see the same effect. There’s something about the seeds being ground up and then stored with some water and at room temperature or a higher temperature that produces hypoglycin A,” Professor Piercy continued.
“We think potentially, this may be a defence mechanism for plants. Potentially hypoglycin A production goes up in the plant material when it’s ground up — in other words, when it’s being eaten.”
Toxicity levels in same tree vary by year
Separate research, which was funded by the Horse Trust, has found that levels of hypoglycin A in the same tree can change from year to year.
Researchers developed a test for measuring the levels of hypoglycin A in a horse’s blood as well as in plant material. The same 14 trees across the middle and south of England were measured for three consecutive years and in 2017 the hypoglycin A levels were higher.
“One of the active areas of investigation for us at the moment is trying to work out, why do sycamore trees produce more hypoglycin A in their in their material in some years compared with others?,” said Professor Piercy.
“We don’t know the answer to that at the moment, but of course that may have a role to play in the susceptibility of horses to the toxin.”
Hypoglycin A remains for weeks
Research has also shown that hypoglycin A remains in sycamore seedlings for several weeks after they’ve been mowed and if you cut sycamore seedlings, the amount of hypoglycin A goes up in the first 48 hours.
If you try to kill sycamore seedlings with herbicides, they retain hypoglycin A.
Professor Piercy believes that some horses may even like the taste of hypoglycin A.
“I think it’s possible, although I don’t have any proof for this, that some horses actually like the taste of hypoglycin A. Maybe they actively try and eat this stuff,” he said.
To help avoid your horse coming into contact with sycamore seedlings, Professor Piercy advises feeding from hay racks so your horse doesn’t eat seedlings on the ground and bringing horses in at night to stop them eating the seeds without knowing about it.
What is atypical myopathy?
When a horse eats sycamore seeds or seedlings, the toxin (hypoglycin A) found in the plant can make its way to the horse’s muscles. This causes the muscle cells to become inactive and even die.
Atypical myopathy has a sudden onset and is fatal in around 70% of affected horses.
Muscle damage commonly affects muscles that are used during standing and breathing, as well as the heart muscle, meaning that a wide range of clinical signs are displayed.
When the muscle cells become damaged, they release muscle enzymes that build up in the organs. This causes further damage, sometimes resulting in multiple organ failure.
Forum highlights
Also at the National Equine Forum, Professor Bruce McGorum revealed that an anti-snake venom drug will be trialled on a small group of horses later this year in an attempt to find a cure for equine grass sickness.
Defra minister Baroness Hayman of Ullock announced that the development of a much-needed digital equine identification and traceability system has been paused by the government due to costs.
Former Retraining of Racehorses chief executive Di Arbuthnot received the Sir Colin Spedding Award in recognition of the thousands of Thoroughbreds her schemes have helped to secure a future for after retiring from the racetrack.
