Unfortunately, following our post on acorn toxicity, we are now also starting to see cases of Atypical Myopathy (AM).

AM is a severe and often fatal muscle disorder caused by ingesting sycamore seeds, leaves, seedlings and possibly, flowers (following heavy wind or rain) which contain a toxin called Hypoglycin A (HGA).  HGA concentrations can vary between trees and even between seeds on the same tree.

Depending on weather conditions, seeds can be blow up to several hundred meters. Therefore, pasture contamination with seeds or seedlings is not necessarily linked to the presence of a tree on the pasture.  It is also REALLY IMPORTANT TO NOTE that horses are at risk even when they have been grazing the same sycamore contaminated pasture for years without incident. The disease is seasonal with the majority of the cases occurring in the autumn coinciding with the fall of the ‘helicopter seeds’ and to a lesser extent in the spring associated with the growth of the seedlings.

HGA  inhibits the production of energy from lipid metabolism and the main clinical signs are related initially to muscle damage and secondarily to kidney damage / organ failure.

In the early stages clinical signs can be vague and difficult to differentiate from other illnesses such as colic or mild laminitis. In more than 50% of cases, the following clinical signs are observed: 

Weakness or struggling to walk.

Recumbency, 

Muscle tremors or fasciculation,

Stiffness or reluctance to move,

Congested mucous membranes,

Sweating,

Signs of colic although, unlike colic, they still have an appetite.

And in the later stages, a full bladder, very dark brown/ red urine (myoglobinuria) and inability to stand.  Some horses also develop heart problems.

Treatment for AM cases is usually directed at supporting the kidneys through oral or IV fluids, ACP, keeping them warm, box rest, offering carbohydrate rich and low fat feeds and supplementing with vitamins and antioxidants but the mortality rate for AM is up to 74%. This is slightly better if referred for intensive care but often it is not possible to transport horses with AM. Horses that survive the first few days of treatment usually go on to recover completely, although this can take several months. Interestingly, some unaffected horses have high concentrations of HGA in their blood suggesting that some horses are more susceptible to the toxin than others.

In light of the high mortality rate and the absence of specific treatment, prevention is the key to avoid intoxication of animals.

At pasture level, the risk can be decreased (1) by avoiding contact with toxic plant material and (2) by favoring low-risk meadows for pasturing during autumn and spring. Additionally, the spreading of manure and/or harrowing of pastures was found to increase the risk of AM. This practice might favor the dispersal of the toxic material throughout the pasture and subsequent intoxication of horses.

It is worth noting that seedlings still contain HGA after herbicidal spraying or mowing. These techniques are therefore ineffective regarding the destruction of toxic material.

Supplementing the pasture with hay can help reduce the overall consumption of potentially toxic material.

If you have sycamore trees on or near your grazing DO NOT TAKE ANY RISKS.

Move horses or fence off the highest risk areas.  Pick up as many leaves, seeds and seedlings as possible or, if possible, sweep / vacuum the pasture. You may be able to create safe ‘parcels’ of fenced off grazing which have been previously cleared.  Additionally, whilst not a great option, limiting grazing time to 6 hours or less has been shown to reduce the risk of AM.

If you have sycamore seeds on your property and want to investigate the HGA risk to your horses samples can be sent to the RVC for analysis. 

If you are in any doubt call us immediately on 01626 819597