Shivers and Stringhalt – Involuntary Leg Movements of the Horse

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What is Equine Shivers?

This is a neurological condition in a horse symptomised by a horse holding up a hind leg which trembles (hence the name Shivers) and often developing to an exaggerated extension backwards of the hind leg when the horse is asked to back up. In extreme cases a horse will stand with both legs stretched out straight behind. Often the tail is held upwards. 

The action of the hindleg makes it difficult for the farrier as picking up the limb will trigger the response. A horse with Shivers can move forward in all paces but it will be seen clearly when the horse is asked to move backwards.

A veterinarian must be requested to examine, and they will diagnose on a clinical basis as there are no blood or other tests that will show any abnormalities.

Statistically male horses are 5 times more likely to develop the syndrome, also the taller horses. It progresses slowly as the horse ages, mostly seen from the age of 5 years but some a few years later. Sometimes it is just one hind limb but often both.

What is the Cause of Equine Shivers?

It is not derived from a muscular origin but purely from an abnormality in the horse’s brain- in the cerebellum. There are cells in the deepest part of the cerebellum called Purkinje cells, and it is these that have shown up to be degenerative in horses with Shivers. This is the area of the brain where movement, co-ordination and fine motor control are managed.

The reason for the degeneration of these cells is assumed to be from inherited genes, although currently these genes have not been identified. Like all research, funds are limited and usually targeted to issues that have the largest number of animals affected.

The problem was prevalent in earlier years in draught horses and so subsequently in warmbloods whose breeding developed form the heavy draught horse. More recently it has also been seen in lighter breeds even the thoroughbred.

Can Equine Shivers be Cured?

There is no cure, however some management of the horse can slow the progress. This being minimising time spent static in a stable, maintaining a good exercise schedule, and science has shown that supplementing with Vitamin E can reduce the symptoms.

Mainly horses with Shivers can generally move forward well, in walk -trot-canter, even jumping, some might show a reaction when moving in small circles or stepping over something, but most carry on in their sport in younger years with not apparent effect unless backing up.

It is likely that the condition will worsen with age, and some muscle reduction in the hindquarters so that the horse is retired early.

What is Equine Stringhalt?

Even though it also an unusual movement of the hind limb, there is a distinct difference in the visible symptoms of Stringhalt. The horse will snatch the limb up and forward and stamp it down. Sometimes up and forward enough to touch the abdomen or hopping. It reacts in this way when asked to move forward in both walk and trot.

Stringhalt can be distressing for both horse and rider, as it can affect the animal’s coordination, balance, and overall performance. It can be mild with some jerky steps, but in severe cases, affected horses may struggle to walk or be ridden safely, impacting their quality of life and usefulness.

Symptoms can be increased if a horse is over excited or nervous, or even turning sharply can trigger the action.

A veterinarian should examine the horse to diagnose as any pain or injury needs to be eliminated and also to assess which type of Stringhalt it may be.

What is the Cause of Equine Stringhalt?

There are two type of stringhalt, one is called Pasture Associated Stringhalt or PSH, and is caused by a horse eating certain weeds that trigger a neurological reaction. It is seasonal as it occurs when plants such as Catsear are growing. Both legs can be affected often showing as a bunny hopping movement, but it is not a permanent state.

This is Catsear which looks like dandelion but the difference is in flower and the leaves and eating Catsear creates damaging neurological effects on horses

Catsear is the most common cause and is very similar to dandelion and so can easily be ignored – but it varies from dandelion in that it has different leaves but more clearly the flowers are on branching stems, the dandelion is a straight single stem. Other plants that may cause PSH are mallow weed and Some lathyrus species, pea plants.

The other cause is called Classic (or true) Stringhalt, and results from damage to the nerves that control hindleg movement. What exactly triggers that damage is currently unknown, but it may also arise from injury to the back or neck, or the hind quarters.

Not all horses exhibit the same symptoms and while some are consistent, others may only show when asked for certain movements or suddenly moving off.

Can Equine Stringhalt be Cured?

PSH can be cured as long as the horse is removed from the pasture that is contaminated with the weeds. Generally, this is overgrazed poor pasture. It may be difficult to totally remove the weed as it has tap roots and is drought resistant. There are sprays that will assist but careful management and improved pasture will be needed to avoid a reoccurrence. Once horses are triggered, they will become more susceptible. Not all horses are affected.

For the horse to recover they must be removed from this pasture for some time. The weeds need to be eradicated, the soil improved and quality grasses planted. It may take some time for the horse to return to normal, often weeks but sometimes many months.

The classic stringhalt will not improve with time but can get progressively worse. Initially It can be helped by some nutritional supplements such as Vitamin E and Vitamin B1 (Thiamine). that have a role in nerve function. Good nutrition generally is needed to support a horse with symptoms.

A course of medication may be suggested by the veterinarian, such as an anticonvulsant Phenytoin, which has been shown to create a significant improvement, but not necessarily a cure. Severe cases have been resolved by surgery called myotenectomy of the lateral digital extensor tendon. This has varied results and is often considered a last resort. A new option is Botox which is experimental at this stage. There is no doubt that Stringhalt does limit the use of the horse but initially will depend on the severity of the symptoms.

It is important that is the case of Shivers or Stringhalt in horses, that a veterinarian is called and requested to diagnose any unusual movements of the limbs.

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