Seasonal pasture myopathy: know the signs

Speed is of the essence when treating a horse with the potentially fatal seasonal condition, atypical myopathy. Andrea Oakes finds out why owners should be vigilant for cases this spring, and how best to plan ahead for autumn

The rapid-onset condition atypical myopathy (AM), which is now known to be linked to trees from the acer family, claimed dozens of equine lives across the UK last autumn as reported cases reached an unprecedented high.

While acers — most notably the sycamore tree — may have stopped shedding their seeds, animals at pasture remain at risk. Studies have shown that small spring outbreaks tend to follow those autumns in which a large number of cases have been reported.

In an attempt to raise awareness of the dangers of AM, vets have urged owners to take precautionary measures and to learn to recognise the most common signs. As H&H reader Jenny Crouch discovered, a little research about this mysterious condition can be a life-saver.

Warning signs

It was autumn 2009 when Jenny’s five-year-old New Forest gelding Peppercorn failed to come to the field gate for his breakfast.

“I knew immediately that something was wrong by the way he was standing,” says Jenny, who called the vet immediately.

“It was a laminitic-type stance. His gut was noisy and he was able to eat and pass droppings, but his head was lowered and he was obviously in pain.”

Jenny’s vet mentioned the possibility of a condition called atypical myoglobinuria, but felt that pelvic, neck or shoulder problems were more likely causes. Peppercorn was given a muscle relaxant while a blood sample was taken for analysis.

“Peppercorn was soon struggling to stay on his feet,” says Jenny. “He hit the ground and within 10 minutes was dead. It all happened within just two-and-a-half hours of us finding him. It was a huge shock.”

Blood test results revealed extremely high levels of the muscle enzymes creatine kinase (CK) and aspartate aminotransferase (AST), confirming AM. But the cause of the condition was at that time unknown.

“It was thought that a bacterium might be a cause, possibly in the pasture, leaves or air,” says Jenny, who closed off the field for winter. “We were focusing on bad weather as a contributing factor.”

A lucky escape

Jenny reopened the field the following spring, but one morning in May spotted her new youngster, Poppy, in a similar stance.

“I shouted for my husband to get the lorry,” says Jenny. “Between us and the vet we manhandled Poppy into it. She could barely take a step.”

Once at hospital, Poppy’s bloods were taken and she was stabled under a heat lamp and placed on an intravenous drip.

“Poppy was a remarkable case,” recalls Richard Parker MRCVS of Endell Veterinary Group.

“Her CK levels were 1,000,000iu/l and AST 400,000iu/l on admission [normal levels should be just a few hundred units]. Thanks to Jenny’s quick action in bringing her in, we were able to stabilise her and gradually nurse her back to health,” says Richard.

“We learnt a great deal from treating Poppy, especially that intensive treatment, if started early enough in the disease process, can be successful. We have since seen many further AM cases, and our survival rates are more than 60%.”

Jenny was able to take Poppy home 10 days later. The mare had lost considerable condition, but with field rest and time made a complete recovery.

Pasture management

Studies at the University of Liège in Belgium and Minnesota University in the US have since confirmed that toxins from the seeds of acer trees are to blame. Armed with this knowledge, Jenny is able to manage her pasture appropriately.

“We’re based in the New Forest national park and have both giant and mid-sized sycamores on our land,” she says.

“By taking them down we will be able to greatly reduce the risk and encourage native trees to grow.

“The predominant westerly wind brings sycamore seeds all the way across our five acres, so keeping the fields clear of them is a nightmare. While there’s no method I know that picks them all up, using a field sweeper on dry grass seems most effective.

“Walk around your paddocks and look at the plants and trees nearby. Be cautious of any acer. Go out in bad weather, too, to learn how the wind affects your pasture — some areas are worse affected with seeds, depending on prevailing wind direction.

“Most importantly, learn the signs and act quickly if you see them. Knowing what we did about Peppercorn helped us save Poppy’s life.”

Jenny has set up an open Facebook page called Equine-Atypical-Myopathy (myoglobinuria) to share information.

To find out more and help with research, go to Liège university’s site, www.myopathie-atypique.be

Ref: Horse & Hound; 5 March 2015