Deidre Carson answers:
Shivers is a disorder of the neuromuscular (muscle and nerve) system.
It was more common in draught breeds when they were used for heavy pulling, but is still seen in different breeds today, including warmbloods and Thoroughbreds. The exact cause is unknown and unfortunately, no treatment is available.
What to watch
One or both hindlimbs may be affected. In classic cases, the horse will hold up a hindlimb rigidly for some time and the limb will ‘shiver’. It’s usually most obvious when the foot is being picked up for shoeing or picking out. Some signs can be exacerbated by excitement.
Other signs include the tail being held out rigidly or to one side, and some severely affected horses are unable to back up. In most cases, the signs progress over a period of time, but many horses can be ridden for years after first signs are seen.
Longer standing cases, however, experience muscle wastage over the hindlimbs and it may not be possible to shoe some affected horses behind, as they could fall over.