Factors that are known to either trigger or cause seizures in susceptible horses.
Many of the factors may be interrelated e.g. hyperthermia and excessive exercise.
Allergies: Food; these are usually related to chemicals and preservatives, rather than the food itself.
Abuse or neglect
Autumn: Research studies have shown that more seizures occur in the autumn. This is due to mould and bacteria in the air and may also be associated with reduced light (photoperiod) affecting the pineal gland (produces melatonin) hypothalamus, pituitary gonadal axis.
Blinking lights: Christmas lights, bright lights, fireworks.
Brain Tumours: Both cancerous and non-cancerous brain tumours can cause seizures
Cysts and cancer
Dryer sheets: If exposed to clothes that have been in the dryer with the dryer sheets.
Environmental pollution from chemical plants
Ethoxyquin: A preservative used in some animal feed whose use began in the late 1980's. To avoid this potential problem use feeds preserved with natural antioxidants such as vitamin E (tocopherol) and vitamin C (ascorbic acid).
Excessive exercise: (see hyperthermia)
Fabric softeners: If exposed to clothes that have fabric softener on them.
Fumes from bleach
Fungi, Bacteria: see infection and mould
Head trauma: A blow to the head from an auto accident, rearing and falling over backwards or hitting the roof of the stable or transporter, abuse or other accident can lead to life-long seizures.
Hereditary Factors. Genetic Factors; Hypercalaemic periodic paralysis (HYPP): Some forms of epilepsy are inherited. Sodium, potassium, and calcium serve the brain as ions and produce electric charges that must fire regularly in order for a steady current to pass from one nerve cell to another. If the channels that carry them are genetically damaged, an imbalance occurs that can cause misfire and cause seizures.
Household cleaners: Pine cleaners should be avoided.
Hyperthermia: Symptoms of heat exhaustion in the horse are; weakness, rapid breathing (the horse's respiration rate may be higher than its heart rate or the horse may be panting), quivering muscles, convulsion and collapse. The body temperature may be elevated to 105 - 108 F, and the horse sweats heavily. Heat exhaustion may occur at any time – during light or heavy work, a few hours after work, or when the horse has not been worked at all. The onset of heat exhaustion may be very gradual.
Heatstroke is a more serious problem where the onset of the problem and the eventual collapse of the horse occur more rapidly than in heat exhaustion. Heatstroke also differs from heat exhaustion in that the horse's body temperature gets much higher (up to 115 F), the horse may get a
vacant, staring expression in its eyes, and the horse stops sweating. During heatstroke, a horse, which has been sweating, rapidly develops a dry coat in which the hairs stand on end. This indicates a severe breakdown of the body's cooling mechanism and rapidly can lead to death of the horse.
Hypoglycaemia / Low blood sugar: Hypoglycaemia, which brings on feelings of fatigue and stress, may be a factor in triggering seizures. Scientists have estimated that between 50 to 90 % of all epileptics suffer from low blood sugar, and 70 % have abnormal glucose tolerance levels. It is a condition that is becoming more common in animals, particularly those suffering from seizures.
Hypothyroidism: An interesting association which has been increasing in frequency is the link between thyroid dysfunction and aberrant behaviour. Typical clinical signs include unprovoked aggression towards other animals and/or people, sudden onset of a seizure disorder in adulthood, disorientation, moodiness, erratic temperament, periods of hyperactivity, hypo-attentiveness, depression, fearfulness and phobias, anxiety, submissiveness, passivity, compulsiveness, and irritability. After the episodes, a majority of the animals were noted to behave as if they were coming out of a trance-like state and were unaware of their previous behaviour.
Although the mechanism whereby diminished thyroid function affects behaviour is unclear, hypothyroid patients have lower cortisol clearance, and the constantly elevated levels of circulating cortisol mimic the condition of an animal in a constant state of stress. They also have lower TSH output and production of thyroid hormones. In humans and dogs, mental function is impaired and the animal is likely to respond to stress in a stereotypical rather than a reasoned way. Chronic stress in humans has been implicated in the pathogenesis of affective disorders such as depression. Major depression has been shown in imaging studies to produce changes in neural activity or volume in areas of the brain that regulate aggressive and other behaviours. Dopamine and serotonin receptors have been clearly demonstrated to be involved in aggressive pathways in the CNS. Hypothyroid rats have increased turnover of serotonin and dopamine receptors, and an increased sensitivity to ambient neurotransmitter levels. In dogs with aberrant aggression, a large collaborative study at Tufts University has shown a favourable response to thyroid replacement therapy within the first week of treatment. A similar pattern of aggression responsive to thyroid replacement has been reported in a horse.
Infection: Any infection where the temperature exceeds 104F may result in convulsions. Venezuelan equine encephalomyelitis (VEE) is a serious viral infection of the nervous system that may cause mental retardation, amnesia, abortion, epilepsy and hidroaencephaly in humans and animals.
Lead, Chemicals, Additives and Poisoning: Toxic metals such as lead, copper, mercury, and aluminium have been known to cause seizures. Some animals are very sensitive to such metals, and exposure is common through aluminium utensils, auto exhaust fumes, industrial pollution, household cleaners and copper water pipes.
Horses grazing Sorghum species have developed a condition known as "equine sorghum cystitis/ataxia syndrome," (The same toxic principle occurs in Sudan grass, Johnson grass, and some other plants if not harvested early enough). Inco-ordination of the hindlimbs, lack of urinary control, and paralysis and inflammation of the bladder can occur.
The unidentified toxic principle causes spinal cord lesions. Pregnant mares may abort, and surviving foals may have musculoskeletal deformities.
Several kinds of trees also are poisonous to horses. Choke cherry, wild black cherry, and pin cherry are common and toxic wild trees. Their leaves and bark contain amygdalin, a material that converts to cyanic or prussic acid as leaves are crushed or wilt, which causes cyanide poisoning when ingested. Cherry often causes poisonings when a tree or branch falls into a horse pasture; the branch wilts, and the horses eat the bark or leaves. Signs of toxicity often are seen within 20 minutes; they include apprehensive behaviour, rapid and laboured respiration, weakness, stumbling, spasms and convulsions, coma, and death. Foaming at the mouth, excessive tearing, and voiding of urine and faeces may occur. Mucous membranes are usually bright and pink, and blood will be a characteristic bright cherry red. Treatment must be administered quickly because death can occur within minutes during severe convulsions.
Once cyanide is absorbed, it is readily transported throughout the body, and is very toxic to all animals. In cells, cyanide reacts with cytochrome oxidase (an enzyme involved in the electron transport system that enables cells to use oxygen) to form a stable, inactive complex. As a result, the cyanide ion inhibits the release of oxygen from the haemoglobin of blood to individual cells. Without oxygen, cellular respiration ceases and cells die rapidly due to hypoxia.
Liver disease: Liver disease is a degenerative inflammatory disease that results in the hardening and scarring of liver cells. The liver becomes unable to function properly due to the scarred tissue, which prevents the normal passage of blood through the liver. If this occurs the sclera (whites of the eye) and mucous membranes may turn yellow (jaundice) and colic and diarrhoea may be experienced. Ammonia build up can result in a condition known as 'brain fog' where the horse exhibits neurological signs such as aimless walking, yawning and running into objects. Weakness, collapse, seizures, coma, and death can occur in severe cases. The cause of liver disease may be due to primary origin or more usually infections and poisoning. Ragwort (Senecio jacobaea), is commonly a cause of liver disease in horses in the United Kingdom, and the plant is becoming an increasing feature within the landscape. The severity of the poisoning depends on the toxin concentration in the plant, the amount eaten, the time span over which it was eaten, and the sensitivity of the horse. Both acute (sudden and severe) and chronic (long-term) poisonings can occur.
Mobile Phones: Research carried out on animals suggests that mobile phone emissions may trigger seizures.
Mould: Aflotoxicosis causes hepatic necrosis and bile duct hyperplasia. Signs include increased temperature, higher respiratory rates, blood stained faeces abdominal straining and convulsions.
Oestrus Cycle: Fluctuating hormones levels have resulted in an increase in seizure severity or quantity in seizure susceptible females that has been attributed to oestrogen.
Feed and herbs that contain natural oestrogens include alfalfa, apples, baker's yeast, barley, beets, carrots, chickpeas, clover, cowpeas (black- eyed peas), fennel, flaxseeds (linseed), garlic, hops, liquorice, oats, olive oil, parsley, peas, potatoes, red beans, red clover, rice, sage, soybeans, split peas, sunflower seeds and wheat.
In Wales potatoes are a traditional feed for fattening/conditioning horses and ponies and in South Africa and Australia rice is a popular concentrate.
Perimenstrual catamenial epilepsy is an increase in seizure frequency that some women experience nearing the time of menstruation that may be related to the withdrawal of the progesterone metabolite allopregnalone.
Oestrogen inhibiting foods that may be relevant to a horses diet are broccoli, buckwheat, cabbage, corn, fruits (except apples, cherries, dates, pomegranates), green beans, melons, millet, tapioca, white rice and white flour.
Plastic: All plastics release some undetectable fumes, especially when heated. This out-gassing means the fumes can pass into the foods that are served or stored in the bowl or container.
Renal Kidney Failure. The role of the kidneys is to remove toxins and excess fluid. When the kidneys become diseased or damaged, they may lose their ability to perform these functions, causing a toxic build-up in the body. Toxins can lead to seizure disorder.
Rabies vaccine: See vaccinations.
Stress: Any change of routine, environment, weaning, travelling and competing can result in stress. This is exhibited by nervous symptoms like excitability, muscle twitching, muscle stiffness, diarrhoea, picky eating, pacing fences/stables, sweating, running a race before it starts, irritability, unpredictable or 'spooky' behaviour, lack of concentration, and unwillingness to work. Stress has an immediate effect on the horse's gut, increasing the rate of passage of food, reducing the ability to digest food and leaving the gut more susceptible to infection by harmful bacteria. The normal healthy balance of gut microflora and allows pathogens to flourish. In the scientific literature stress has been linked to deficiencies of B Group vitamins and magnesium.
Sugar: Sucrose, corn syrup, molasses, cane sugar and Low quality commercial compounded feeds.
Toxic Shampoos: See Lead, Chemicals, Additives and Poisoning.
Vaccinations: Because vaccines may contain proteins and/or organisms and heavy metals, they may produce an allergic inflammation of the brain.
Some holistically oriented veterinarians feel that over-vaccination with yearly vaccines may also predispose pets to epilepsy. Though there have not been any definitive studies concerning this matter, there has been sufficient evidence suggesting that we need not vaccinate our pets annually anyway. Check with a respected holistically oriented veterinarian in regards to this matter.
Vitamins with high sodium level: See also Lead, Chemicals, Additives and Poisoning. Salt, Ferrous Sulfate, Copper Sulfate, Calcium Iodate, Sodium nitrate have been proven in research studies to cause severe seizures.
Vitamin and mineral deficiencies may be a possible cause of seizure. Research indicates that the key nutrients that appear deficient in epileptics are vitamin B6, vitamin A, folic acid, vitamin D, zinc, taurine, magnesium, and calcium. Vitamin B6 deficiencies have been reported to produce neurological abnormalities resembling epilepsy. Feeding these nutrients to horses helps restore normal nervous function and produce a soothing effect. Deficiencies of B-group vitamins (B1, B2, B6 & niacin), magnesium and tryptophan have been linked to nervous symptoms and accordingly the feeding of high doses of vitamin Bl (thiamine) has been used to produce a calming effect. Magnesium has also been administered to relieve nervous symptoms in grain-fed horses while tryptophan has been used as a mood stabiliser, particularly in conjunction with magnesium and vitamin B6.
Worm infestation: Parasites release toxins that have an adverse affect on the central nervous system.
Wormwood:("absinthe" or Artemesia absinthium), may be found in herbal anti-parasitic/anthelmintics preparations. Chronic use leads to severe neurotoxicity, tremors, hallucinations and seizures.
A seizure refers to the involuntary contraction of muscles. The seizure is caused by an electrical storm in the brain and can be catagorised by two types:
1. Generalized 'Grand mal' or 'major motor' or 'tonic-clonic' seizure are the most severe. In a generalized seizure, the electrical storm appears everywhere at once.
he seizure begins with contraction of all skeletal muscles and loss of consciousness. The animal usually falls to its side with the legs stretched out and the head back. This is the tonic portion of the seizure. Sometimes it will vocalize or have facial twitching. Vocalizations are involuntary and do not indicate pain. The animal may salivate, urinate and defecate.
The tonic portion of the seizure is usually very brief and gives way to the clonic phase of the seizure. Once the clonic phase begins the animal will have rhythmic movements. Typically this consists of clamping the jaws and jerking or running movements of the legs.
Not all generalized seizures follow this pattern. Another type of generalized seizure is the tonic seizure, in which motor activity consists only of generalized muscle rigidity without the clonic phase. Less common are clonic seizures where there is no tonic phase and some animals suffer milder generalized tonic-clonic seizures in which consciousness is maintained.
The seizure may last a few minutes and following the seizure, the horse may lay motionless for a brief it will get up onto its feet and may appear to be perfectly normal, but typically will show signs of postictal behaviour. These signs may include blindness, disorientation, pacing or running about the house bumping into things. The postictal behaviour can last anywhere from hours to days after a seizure.
2. Infrequent or 'partial motor seizures' or 'Petit mal' focal seizure is a less severe form of epilepsy, which affects only a specific group or groups of muscles whose innervation begin in a small area of the brain. Because the seizure starts in only a part of the brain, an underlying disease or injury is highly suspected.
Partial seizures are classified as simple focal seizures when consciousness is preserved and as complex focal seizures when consciousness is altered. Any portion of the body may be involved during a focal seizure depending on the region of the brain affected.
In a simple partial seizure, the area of the brain that is affected is the area that controls movement. Usually the face is affected, resulting in twitching or blinking.
This is usually limited to one side of the face. The horse may appear drowsy or sleepy (narcolepsy). If the seizure spreads, other parts of the body on that same side will be affected.
A complex partial seizure will originate in the area of the brain that controls behaviour and is sometimes called a psychomotor seizure. During this type of seizure, consciousness is altered and bizarre behaviour such as unprovoked aggression or irrational fear may be exhibited. The horse may run uncontrollably or engage in senseless, repetitive behaviour. A partial seizure may remain localized or spread to other parts of the cerebral cortex producing a sequential involvement of other body parts.
Diagnosis is based on signs and
tests such as blood tests, (cell counts, immnoglobulins, protein, enzymes, hormone levels, poisons), X-rays, cerebrospinal fluid taps, electroencephalograms, magnetic resonance imaging (MRI) and neurological and ophthalmic examination that may help to provide a cause for the seizures.
A complete history should be taken by the veterinarian that will help to eliminate other health problems or enable treatment.
Due to the scale of the animal involved, its temperament and psychology, the present limitations and availability of the technologies, not all the possible diagnostic technologies may be available to you and your horse.
A diary of all seizure activity (dates, description, duration, drugs) should be kept by the owner.
Immediately after a seizure check the horse's temperature. Seizures and muscle activity cause hyperthermia and rubbing alcohol (surgical spirit) or cool water can be used to lower the temperature if necessary.
If multiple seizures have occurred with little to no recovery in-between, and the horse is within an equine veterinary facility; oxygen, corticosteroids or mannitol to decrease cerebral oedema from hypoxia or hypoglycemia may be administered.
If seizures occur more than once every month or after the second or third seizure the veterinarian may prescribe anticonvulsants.
Phenobarbital, Primidone, Diazepam (Valium) and Potassium Bromide (KBr) are typically prescribed for seizure disorders.
Phenobarbital is clinically effective within 12-24 hours after oral administration. Advantages are that it is safe and inexpensive.
Primidon (Mylepsin®, Mysoline®)
Advantages are as above. It is metabolized to phenobarbital and phenylethylmalonic acid (PEMA) which have anticonvulsant effects. The Phenobarbital component of primidone may be the major anticonvulsant metabolite.
Potassium bromide (KBr)
is not a licensed medication in the United States, while currently in the United Kingdom it is classed as a supplement. In Veterinary Medicinepotassium bromide is a superior anticonvulsant medication than phenobarbital. It seems to be more effective and have fewer undesirable side effects.
KBr works by competing with chloride ions for access to brain tissues. As bromide levels in the brain rise and chloride levels drop, electrical activity in the central nervous system is inhibited thereby blocking the initiation of a seizure.
KBr is generally reserved for animals that cannot tolerate phenobarbital for seizure control due to unacceptable side effects or lack of effectiveness. It is can be mixed in water and provided as a liquid solution or can be mixed in feed. When potassium bromide therapy is initiated in a patient it is common to begin with a "loading dose," a very high dose given for a short period of time to get the blood level up more quickly.
The use of potassium bromide as a sole seizure control agent is currently under investigation. Typically the use of potassium bromide allows for a reduction of phenobarbital use by 30-50% which is usually enough to alleviate the negative side effects of phenobarbital.
Side Effects: Common side effects of many anticonvulsants include sedation, ataxia, excessive sleep, increased thirst, weakness, muscle tremors and pain, constipation, increased urination, appetite loss and increased appetite. These side effects often disappear several days after starting the drug. If other side effects appear or if the above side effects do not disappear they should be discussed with your veterinarian. There is the potential for liver damage, bone marrow damage, kidney damage, foetal malformations and allergic reactions.
If the medication is stopped promptly these side effects are usually reversible.
The horse's diary or seizure chart should be reviewed at least yearly (at the time of yearly vaccine)or sooner if the seizures are occurring more than once every 2 months. If there are problems with seizure control, a serum anticonvulsant level can be taken to assess whether serum levels are appropriate enough to control the seizure.
There are some cases that eventually become refractory (i.e. seizures that are difficult to control using anticonvulsants).
Reasons for Drug Failure
Changing patterns of seizure activity may indicate ineffective or improperly administered
medication, or the presence of other diseases.
Reviewing the diary or chart of seizure activity will help decide if other diagnostic or therapeutic steps need to be taken.
Drug interactions: Some drugs cause a decrease in the serum concentrations of the anticonvulsant drug.
Wrong diagnosis or progressive diseases that may not be controlled with anticonvulsants e.g. brain tumours, shunts, insulinomas or other causes of hypoglycemia.
Development of tolerance: Increasing the dose or frequency of administration of the anticonvulsant drug will usually control the seizures again.
Use of drugs known to stimulate seizures: Avoid amphetamines and phenothiazine tranquilizers such as acepromazine (ACP) and anthelmintics group ivermectin, avermectin, moxidectin.
Oestrus, stress, or excitement may cause an increase or severity of seizures.
Increasing the dose a few days before the anticipated excitement may alleviate the problem.
When to stop anticonvulsant therapy
If the horse has been seizure-free for at least 6 months, your veterinarian may advise gradually decreasing the anticonvulsant over a 4-8 week period. If seizures re-occur, it is likely that medication at original dosage should be resumed indefinitely.
Complementary therapies, adjuncts and adjuvants
Although drug therapy can be very effective, some may cause side effects that can eventually cause other problems. Many owners are receptive to adjuncts and complementary methods of treating seizure disorders. These include homeopathy, chiropractors, acupuncture and herbal medicine and should be discussed with your veterinarian as to suitability of application to you horse.
Acupuncture appears to be a useful adjunct to treatment of seizures. Frequent treatments are usually necessary, so gold bead implants (a type of long-term stimulation) are commonly recommended. This is a surgical procedure available from most veterinary acupuncturists. Traditional Chinese acupuncture once a week for four to six weeks and then tapering off treatments to once every month or two, can have excellent results.
Herbs that may be beneficial as sedatives or antianxiolytic include valerian root, skullcap, oatstraw and kava. The dosage of other anticonvulsants may need to be lower when using herbs and supplements.
MSM for horses relieves a variety of horse ailments by reducing inflammation and enhancing blood circulation.
Melatonin has been found to be helpful when treating dogs who have "thunder-phobia," other noise-related reactions and stressful situations. Melatonin has been used effectively to reduce seizures in dogs that suffer seizure between 11:00 PM and 6:00 AM. It also seems to lessen the frequency and/or severity of seizures at other times of the day.
Bach Original Flower Rescue Remedy can be used in many different ways; after a seizure to reduce pacing and other postictal behaviours and to reduce stress in a variety of situations, either "good" or "bad" stress, that may potentially lead to seizure activity.
By reducing the effects of the stressor on the system, seizures may be prevented or the severity and/or number decreased.
Many veterinarians treating animals suffering from seizure disorders appreciate that alternative nutritional management is an important step in minimizing their patients' environmental challenges. The results of this approach have been remarkable. Standard commercial diets containing synthetic chemical preservatives are replaced with naturally preserved foods. The replacement food must be of good quality and preferably of relatively low protein content. Increasing carbohydrate and reducing protein content, while maintaining high quality protein, has been shown to be beneficial for many affected animals and is also believed to have a positive effect on behaviour.
Other nutraceutical and dietary supplements that appear to decrease the incidence of seizures. Those mentioned in the human literature include vitamin B6, folic acid, pyridoxine, magnesium, manganese, zinc, selenium, choline, dimethylglycine (DMG), and taurine. Tryptophan is known to be effective as a mood stabiliser, particularly in conjunction with magnesium and vitamin B6. Even horses whose diets are not lacking these nutrients may show reduced symptoms of stress when their diets are supplemented with the above together with the
antioxidant vitamins C, E. Vitamin C is absolutely essential to the living process and although horses do produce vitamin C, stress, vaccinations, illness, skin problems, anthelmintics (wormers) deplete the amount produced.
Multi-strain probiotics and prebiotics may be useful in helping to ensure the health of the digestive system
This suggests that all horses suffering from seizures should, be taking a high quality vitamin-mineral supplement, and your veterinarian and nutritionist should be consulted for higher dosages of specific nutrients, if appropriate.