From our conversations with clients, atypical myopathy is either something that you have never heard of, or something that you and your horsey friends have been hugely worried about. Several cases have been reported the Hampshire area recently and vets are on the alert for any signs of it affecting more horses.

For those of you not in the know, atypical myopathy (AM) is a nasty condition affecting the postural, respiratory (breathing) and cardiac (heart) muscles of the horse. It is not known what causes AM (although we think it is a toxin of some sort) but it only occurs in horses that have access to grazing.

It usually affects young or old horses that are in lean to poor body condition. and is more common in fields that have rivers or streams adjacent to them. It tends to occur in mild damp autumns like we are having now, but some cases are seen in spring. Cases are very uncommon once we have had several frosty nights.

Horses that develop AM are often found down in the field, unable to get up. It can look a little like colic but affected horses maintain a good appetitie,often grazing whilst lying down.

The classic clinical sign is a dark red colouration to the urine. Early cases may be reluctant to move with a few showing odd behaviour (such as repeated vocalisation,difficulty swallowing and head tossing) for a day or two before. Treatment is difficult and unfortunately often inneffective – approximately 70% of affected horses die.

Supportive treatment such as intravenous fluids and good nursing care may help. Any horse grazing in the same field as those affected should be stabled immediately.

Thankfully, atypical myopathy is still a rare condition. The only way that we can seem to prevent atypical myopathy is to reduce the amount of grazing that horses get either by stabling or by restricting the field size and supplementing with hay. Hay should be fed from a bucket or net, not from the floor and droppings should be collected rather than harrowed in.

If a horse has suffered from the condition previously,all horses should be removed from that field during risk periods.

Let’s keep our fingers crossed for a few frosty nights then we can stop worrying!