LATE on Friday evening, the phone jumped into life with a frantic call. It was a pony with colic and could I come out to see it straight away? The pony was a middle-aged gelding who was loved to bits by his doting owner. She had thought he was a little bit lethargic earlier in the week but now he was inclined to go down and was looking quite out of sorts for himself.

Bruno looked a bit quiet when I arrived and a thorough clinical examination did not shed much light on the situation. Apart from being a bit stiff and having some dry faeces in his bowel, it was hard to pinpoint any real cause of colic.

We made Bruno as comfortable as possible for the night using painkillers and a muscle relaxant and left him with an anxious Dad to keep an eye on him through the wee hours. As part of the examination we had queried whether any old ivy or evergreen plants had been eaten by Bruno in the preceding days and Dad had rechecked the paddock in search of same. We agreed to look in on Bruno early on Saturday morning and duly arrived at the stable at sun-up. Dad had spent the night watching over Bruno and gave us a blow by blow report on how the night had gone. No faeces had passed and things had not really moved on too much over the night-time hours.

The heart rate had increased a bit despite the medication and we decided to move Bruno to the Veterinary Hospital for a more aggressive treatment regimen. A neighbour very kindly obliged with his jeep and box and before long we had Bruno safely admitted and up on a drip to restore his fluid balance.

And that’s when the first true signs of the problem reared its ugly head. Bruno passed one seriously large amount of bloody coloured urine and we immediately feared we were in for the worst.

We feared Bruno was suffering from a condition known as “Atypical Myopathy” (AM) and that the prognosis was not too good. This condition occurs in very specific conditions of long dry autumns with horses grazing old pastures overlayed with recently fallen sycamore seeds.

Michael Sadlier MVB MRCVS of Veterinary Ireland and Troytown Equine Hospital wrote an excellent article in The Irish Field in April of this year and we feel it’s a good time to re-run that article here for your perusal. It makes for stark reading and will give you an insight as to what faced us with Bruno once the bloody urine was produced. Please don’t ask me to tell you how we got on with Bruno. Just read the article and watch out for those falling sycamore seeds.

ATYPICAL MYOPATHY

Equine Atypical Myopathy, also known as Atypical Myoglobinuria, is a frequently fatal condition affecting autumn and/or spring grazing horses. The disease clinical signs seem to appear after occurrence of specific climatic conditions. The condition has been recognised in 1984.

A typical story is of a horse starting by showing stiffness and a reluctance to move. His muscles suddenly become weak to the point he can no longer remain standing. Then, as quickly as clinical signs set in, the horse dies. Just 48 hours earlier the horse grazed happily in his pasture - an overgrazed field full of seed heads and dead leaves.

This story is typical of suspected cases of seasonal pasture myopathy (SPM), a highly fatal muscle disease described in the midwestern United States and eastern Canada, and atypical myopathy (AM) in the UK and Europe

Horses that develop Atypical Myoglobinuria are usually kept on sparse pastures with an accumulation of dead leaves, dead wood, and trees in or around the pastures.

Unlike other muscle disorders, the disease’s clinical signs are not associated with exercise and include:

These clinical signs progress quickly with rapid respiratory rate within 48 hours and dyspnoea (difficulty breathing) and death within 72 hours in at least 75% of cases. The cause of death is a very specific metabolic block in the muscle’s ability to burn fat for fuel.

In 2011 Stephanie Valberg, DVM, Dipl. ACVIM, and a team of researchers from University of Minnesota (UM) and Iowa State University (ISU) started investigating SPM cases and found a link to box elder trees. She presented their findings in “Identification of the Cause of Seasonal Pasture Myopathy in Horses” at the 2014 American College of Veterinary Medicine Forum, held in Seattle, Washington.

The common features for this condition were little supplemental feeding and prolonged grazing of sparse pastures that were in close proximity to seed-laden box elder trees. Testing found that one amino acid, hypoglycin A, was “highly abundant” in the box elder seeds.

This amino acid, also found in unripe fruit of the ackee tree (within the same tree family as box elder), is known to block the same specific enzyme in fat metabolism in humans as was seen in SPM-afflicted horses.

Most recently, scientists have found another related tree, the European sycamore maple tree (Acer pseudoplatanus), in northern European pastures where horses have died from Atypical Myoglobinuria. European sycamore maple seeds also contain hypoglycin A.

A paper published in the March 2014 edition of the Equine Veterinary Journal by Votion et al concluded that Atypical Myopathy in Europe, like seasonal pasture myopathy in North America, is highly associated with the toxic metabolite of hypoglycin A. MCPA-carnitine. This finding coupled with the presence of a tree of which whose seeds are known to also contain hypoglycin A indicates that ingestion of Acer pseudoplatanus (sycamore tree seeds) is the probable cause of Atypical Myopathy. This finding has major implications for the prevention of Atypical Myopathy or Myoglobinuria.

Protecting your horses

Young horses and those new to an affected pasture appear to be at great risk if:

Removal of the box elder or European sycamore trees from affected pastures can be one approach, although, this might not always be feasible.

While box elders rarely live longer than 50 years, some of the sycamore maples on affected pastures are huge beautiful trees that owners may be very reluctant to remove.

In cases where the trees can’t be removed, it is recommended decreasing turnout time on affected pastures from October through mid-December and in the early spring.

Other important preventive measures could include providing additional forage if pastures are overgrazed, preventing over grazing of pastures through rotational grazing and limiting turnout to less than 12 hours per day during autumn and early spring.

Peadar Ó Scanaill and Michael Sadlier are members of the Equine Group of Veterinary Ireland. Peadar is in practice in Ashbourne, Co Meath while Michael is a partner in Troytown/Grey Abbey Veterinary Hospital, Co Kildare.

Email: hq@vetireland.ie

Telephone: 01-4577976