Understanding equine fits

The words “fit”, or “seizure”, conjure up frightening images of a frothing, thrashing, frenzy. Indeed, it can be very distressing to witness, whether a person or an animal is involved. Happily, true fits are relatively uncommon within the equine world — and adult horses especially appear to have a high seizure threshold compared with other species. Inherited epilepsy, a cause of seizures among dogs, probably does not even occur in horses at all.

A fit, or seizure, is not a condition in itself. Rather it is the term used to describe what happens when something else causes rapid excessive electrical impulses to be discharged from certain parts of the brain (usually the cerebral cortex). These chaotic impulses often result in extreme involuntary movements together with a variable loss of consciousness, sensation and normal bodily functioning — known collectively as fits.

Fits should therefore be regarded as an indication of some other condition, and this is what your vet will be considering when investigating such a problem.

Fits can be separated into two types:

• Partial seizures: only a limited discrete area of the brain is involved, leading to localised signs, such as facial or limb twitching, pacing circles or self-harming.
• General seizures: most, or all, of the cerebral cortex is affected, leading to fits involving the whole body, with total loss of consciousness.

Another sort of fit is caused by infection; either extracranial — bacterial septicaemia, fever, tetanus, botulism; or intracranial — bacterial meningitis, brain abscesses, rabies, viral encephalitis.

Common causes of fits

• Neonatal maladjustment syndrome: called “barkers and wanderers”, or “hypoxic ischaemic encephalopathy” — thought to be due to some sort of physical trauma or asphyxiation to the foal during or immediately after birth, causing haemorrhage and/or oxygen starvation to the heart and brain. Such foals may appear normal at first, but six to 24hr later symptoms such as disorientation, lack of co-ordination, aimless wandering, blindness, odd whinnying and seizures begin. This condition carries a guarded prognosis and veterinary attention should be sought immediately.
• Bacterial meningitis/brain abscesses: these are uncommon in adults, although there have been reports of infections following an outbreak of strangles. Once again, foals are more at risk, especially those that don’t take in sufficient colostrum at birth. Multiple bugs are often involved, with a brain infection following on from a generalised septicaemia.
• Hepatoencephalopathy: severe liver damage leads to the impairment of protein, fat and carbohydrate metabolism and the detoxification of nitrogen waste, resulting in irreversible brain damage. Ragwort remains the most common cause of liver damage in adults, while infection with the bug Bacillus piliformis (known as Tyzzer’s disease) occurs less commonly in foals. Typical signs include anorexia, depression, dementia, violent frenzies, compulsive circling, head pressing, yawning, blindness and convulsions.
• Toxicities: bracken, if eaten in sufficient quantities, can lead to a thiamine deficiency, causing wobbliness, seizures and even death. Lead poisoning used to be recognised in animals grazing near smelting industries. It is only rarely encountered these days.

What do fits look like?

The signs will vary depending on the area and extent of the brain involved. Partial fits can be very subtle. Often there is only a degree of facial and/or limb twitching, but there may be other signs, such as excessive chewing, compulsive pacing or self-mutilation, where the horse seems intent on biting or gnawing itself.

Generalised fits are easier to recognise and tend to occur in three phases. First of all the “aura” (period just prior to the fit itself) — the horse may appear anxious and unsettled.

Then comes “ictus” (the fit itself) — the horse will probably lie down and become unconscious or unaware of its surroundings; a series of symmetrical (“clonic”) muscle contraction and relaxation cycles may be followed by continuous, unrelenting (“tonic”) muscle contractions, making the horse appear stiff and rigid.

Other characteristics include deviation of the eyeballs, dilated pupils and protruding eyes, jaw clamping and excessive salivation, arching or curving of the back, violent limb paddling, and involuntary wetting and defecation. This phase usually lasts for less than a minute, although it will appear like an eternity to anyone present.

Finally, the “post-ictal phase” (period after the fit) — the horse will often appear depressed and partially blind for hours, or even days.

All of this makes for a highly frightening scenario, but it should be stressed that a full-blown generalised fit in an adult horse or pony is very rare. Neither should fits be confused with any of the following:

• occasional aberrant behaviour, such as extreme nappiness
• an odd stereotypical pattern, such as a horse I once saw that twisted its head up in the air, hung its tongue out of the side of its mouth and drooled excessively whenever it was highly stressed
• an extreme reaction to something in the environment, such as a fly bite or nettle stings, or to pain associated with conditions such as colic, tying up or even a fractured limb. The fact that the animal remains conscious and bright with these distinguishes them from true fits.
• This veterinary feature was first published in Horse & Hound
• To read more expert advice on veterinary problems visit HHO’s horse care archive at www.horseandhound.co.uk/horsecare/