Shivers in horses: cause, recognition and management

What exactly happens with shivers?

With shivers, the coordination between nerves and muscles in the hind legs becomes disrupted. When your horse lifts a hind leg, the leg involuntarily pulls upward and toward the belly, the muscles tremble, and the leg may momentarily 'hang' in that position before dropping back down. This can look abrupt or spasmodic. In more severe cases it also occurs when backing up. The exact cause has not yet been fully clarified, but researchers suspect that the cerebellum — the part of the brain that coordinates movement — plays a role. Heredity also appears to be a factor.

Recognise the early signs

Early intervention makes a difference. Look out for these characteristics:

• Trembling or jerking hind leg when lifted, even briefly
• The leg is pulled higher than normal during lifting
• Difficulty backing up or refusal to do so
• Muscle loss in the hindquarter and thigh muscles in advanced stages
• Discomfort or tension during farrier or veterinary visits

How does the vet make the diagnosis?

There is no simple blood test or imaging test that directly confirms shivers. The vet bases the diagnosis on a clinical examination: lifting the hind legs, asking the horse to back up, and assessing the movement pattern. Sometimes a biopsy of muscle fibres is taken to rule out other muscle conditions. Differential diagnoses include stringhalt — a similar but distinct condition — and various muscle disorders such as PSSM (polysaccharide storage myopathy). PSSM and shivers can, incidentally, occur together, which can complicate the picture. Record your observations from home in the EquiSight horse profile, so you can give the vet a complete picture.

Shivers versus stringhalt: the differences

• Stringhalt: the leg shoots rapidly upward and back with every step; shivers: only when the leg is deliberately lifted
• Stringhalt: often sudden in onset, sometimes after grazing on certain plants; shivers: gradual onset
• Stringhalt: both hind legs can be affected simultaneously; shivers: usually starts on one side
• Stringhalt: sometimes has a toxic cause and can improve spontaneously; shivers is chronic
• When in doubt, the vet decides based on movement examination and case history

What can you do yourself?

There is no cure for shivers, but you can slow the progression and improve your horse's comfort. Nutrition plays a major role: a high-fat, low-starch diet helps, especially if PSSM is also present. Aim for a diet with a maximum of 10–12% starch and sugar on a dry matter basis. Regular, light exercise is better than fluctuating workloads. Avoid long periods in the stable without movement. Some horses respond well to whey protein as a nutritional supplement. Work together with a nutritionist and record all changes and responses in the EquiSight calendar, so you can identify patterns over a longer period of time.

Riding and sport: what is still possible?

Many horses in an early stage of shivers can remain in regular work, provided you are realistic about expectations. Sport horses competing at a high level will sooner or later need to step back. At recreational level, riding is possible in most cases, as long as the horse is not in pain and has sufficient freedom of movement. Have the farrier visit more frequently — shorter intervals of 5 to 6 weeks can help, as long-grown hooves put strain on balance. Discuss with your vet or physiotherapist which exercises contribute to muscle mass and balance without overloading.