Category: Clinical Directors

Choosing To Breed

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Making the decision to breed from your mare should not be taken lightly. There are many unwanted and neglected horses that could have been avoided if people did not breed carelessly and without thought. Therefore I consider the primary question you should be asking yourself now is:
“Why are you breeding from your mare?”

Are you choosing to breed because your mare is a much loved pony that your family has now outgrown? If this is the case will the potential foal actually be suitable for your purpose or in fact be too small? Putting a big stallion to a small mare will not guarantee an offspring half way in-between - like humans they may take after the father or the mother. Before you breed because of sentimental reasons, ask yourself is your mare of good enough type or does she have faults that you are choosing not to see?

A common explanation I hear is that people are putting a mare in foal because she is too sharp or difficult in temperament to be ridden, which is a terrible reason to decide to breed. Temperament is certainly hereditary and a horse with a difficult nature is likely to pass this onto the foal, and even at a professional level, horses need to have both ability and a trainable disposition.

Breeding because of injury to the mare also needs to be considered carefully, as potentially the weakness or a predisposition to the injury may be directly hereditary or the conformational attributes that predisposed the injury may be inherited. If you have any concerns regarding this point you should discuss the situation with your own vet before proceeding.
Breeding to sell or breeding to keep? Sadly the notion that you can make lots of money breeding horses seems to rarely eventuate especially if you do not have your own property. The potential cost of breeding a single foal for you to keep is likely to far exceed the cost of buying one already grown. You need to consider firstly the cost of putting your mare in foal including veterinary fees and stud fees. Then you should add the potential livery costs for the mare while she is in foal, then with the foal at foot and once the foal is weaned. Where are you going to foal the mare down and how much will that cost? When do you plan to sell the progeny, as a foal, yearling or once they are being ridden and consequently what will the cost be of keeping them until that point? Will you insure the foal and what will the costs be for vaccinations, passport, microchipping, castration and other unexpected injuries or illnesses?

If you are planning on selling the offspring what is the realistic amount you are likely to get for them and how does this compare with the actual cost of producing a horse from birth to the point of sale? Even using the best of bloodlines for both the sire and dam does not guarantee a potential superstar and high value off-spring.

That said, there is nothing quite like the satisfaction of competing on a horse you have watched come into the world and produced through the grades yourself. In addition, not all horses have to be professional athletes and breeding from a sentimentally valuable mare to produce a pleasure horse that will be loved and have a happy home for life cannot be considered a bad thing to do. So if after considering the question "why are you breeding from your mare?", you are still keen to proceed then it is time to contact your stud veterinarian to discuss your individual situation.

Worms & Worming

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Red Worms

 

There are numerous types of gastrointestinal parasites or “worms” as they are more frequently referred as. Worms are a burden on the horse’s gastrointestinal tract (GIT). This burden can range from being completely sub-clinical (the horse shows no ill effects from the infestation) to reducing a horse’s performance in events, causing colic, diarrhoea, weight loss and in severe cases horses can die as a result of parasitic infestation.

The most common and pathogenic worms that infest horses are, cyathostomins (small worms or small redworms), large strongyles (large red worms) and tapeworms. Large red worms were historically a problem but are now far less prevalent and cause less clinical disease. Small red worms are very common affecting all ages but mainly young horses (1-4 years old). Most infections are subclinical.

The small red worm life cycle: the larvae are eaten by the horse off the pasture and move through the GIT. They then burrow into the gut wall and can stay there for weeks, months or even years. They stay there until conditions are just right then they emerge from the gut wall and mature into adults where the adults produce eggs that are shed in the faeces. The eggs in the faeces then develop on the pasture into the larvae that are eaten and so the cycle continues.

The larvae in the gut wall are called “encysted” and these are very difficult to treat. Only two drugs can target these encysted larvae: a 5 day course of Fenbendazole or Moxidectin. If a large number of worms erupt from the gut wall at the same time then horses can develop severe problems. Encysted larvae don't produce eggs and so it is important to remember that a horse can have a low faecal egg count (FEC) but still have a high worm burden.

The tapeworm life cycle is different as they don't burrow into the wall but they shed their eggs intermittently so a negative WEC does not mean no tapeworms. A high tapeworm burden can cause colic. A blood test is available to detect antibodies against tapeworms, but this only gives an indication that they have been exposed at some point in the last 6 months.

Wormers Red Worms  Tapeworm
  Adults  Encysted Larvae Annual/6 month dose
1 d Fenbendazole     √    χ     χ
5 d Fendendazole     √    √        χ

Pyrantel      

   √    χ

   √  

double dose
Ivermectin       √    χ    χ
Moxidectin 

  √  

    √     χ
Praziquantel     χ    χ     √

 

Anthelmintic “wormers” have different effects and so target different worms at different stages of their life cycle. This table shows which worms are killed by the different active ingredients in wormers.

80% of worms produced in a field come from 20% of the horses. This means that the majority of horses on a pasture have few worms and so produce only a very small number of eggs. These horses are ‘low egg shedders’ and they do not need worming as they won’t be suffering adverse effects of having worms and won’t be significantly contributing to pasture contamination. The small group of horses that make up the 20% will be ‘high egg shedders’. These horses will have a FEC>200 eggs per gram. For an unknown reason these horses will be persistent egg shedders despite the same or similar pasture management as their herd mates. It is these horses we need to target with wormers to reduce pasture contamination and infectivity.

Each time you worm your horse a small number of the worms present will be resistant or “immune” to the effects of the wormers you use and so will survive worming. If you repeatedly give the same type of wormer to all horses on the pasture, over time the number of resistant worms in your horses' GIT will increase until all the worms are resistant and your wormer will no longer work. The oldest wormers (Fenbendazoles) have the highest resistance and the newest wormers have the least resistance (Moxidectin). It is important to understand that there are no new wormers being generated. Donkeys are already resistant to Moxidectin.

If you are worried about resistance developing on your yard then your vet can perform a faecal egg count reduction test (FECRT). This test measures the efficacy of the wormer you have used.

To reduce the development of resistance we can do four things:

1. Allow a population of sensitive worms “refugia” to survive the worming process. These refugee worms will dilute and compete with the resistant worms for resources. This competition will stop the development of an entirely resistant population. To do this we have to use a targeted worming protocol.

2. Reduce the use of wormers by only worming those horses with a FEC above 200 epg.

3. Manage the environment to minimise our reliance of wormers. We can do this by reducing the number of horses per acre, regular poo picking (everyone’s favourite summer pastime), mixed grazing with sheep and cattle and finally harrowing fields on hot dry days so the sun destroys the eggs in the soil.

4. Quarantine new horses so they don't bring resistant worms onto the yard. New horses should also be wormed for tapeworm and encysted larvae before being turned out.

Worming Programmes:

Firstly, no one protocol will work for every yard and if you have any concerns please consult your vet about your specific yard requirements so we can tailor a programme for you.

Regular worming - worming every 4-6 weeks will reduce disease BUT will lead to resistance and a shift in the type of worms you will see, so this is NOT a sustainable management protocol. Worming at specific times of the year can be successful in disrupting the worms' life cycle, however, changes in weather pattern or the introduction of heavily contaminated individuals will reduce your success and won’t help heavily burdened horses.

Targeted worming - treating each horse as an individual is the BEST strategy. You must use a FEC to select those horses who are shedding >200 epg and only worm those horses, the “high egg shedders”. By doing this you will reduce pasture contamination and reduce the development of resistance. It is also a CHEAPER worming protocol. You must have a FEC from every horse because 80% of the worms are produced by 20% of the horses so in a herd of 30 horses only 6 will be significantly shedding eggs but you won’t know which six unless you sample all 30.

We recommend that as part of any worming strategy, tapeworm should be targeted twice a year in autumn and spring, and that encysted worms are targeted in winter.

Chris Baldwin, BVetMed, MRCVS

Tetanus

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All horses, ponies and donkeys should be vaccinated against tetanus, a condition that equine species are very susceptible to. Sadly, most cases die, very few live and a huge amount of time, money and effort is required to keep them alive if they do survive. Vaccination against tetanus is very effective.

Tetanus is caused by a bacteria called Clostridium tetani that lives in the soil, the horse's digestive tract and the environment. This bug likes to propagate itself in places that do not have much oxygen, an anaerobic bacteria. Usually horses become infected after a puncture type wound becomes contaminated with the Clostridium bug, a deep wound is an ideal oxygen free site for the bacteria to multiply. Other types of injury that can lead to problems with tetanus would include puncture wounds to the foot and wounds within the mouth.

It is important to keep a close eye on wounds that are quite small externally that may have punctured deeper into the tissues than first thought. It is particularly important to check horses out in the field with thick coats or wearing rugs in winter.

The spores from the Clostridium bacteria produce a series of neurotoxins that are circulated around the body in the blood stream and enter the central nervous system. The main neurotoxin is neurospasmic and it is these neurotoxins that cause the problem and the clinical picture that we see with horses with tetanus. The neurotoxins cause a spasm of muscles, without really any twitching. This is a tetanic type of contraction, hence the name “tetanus”.

The classic symptoms of tetanus are initially a stiff legged gait and almost a saw-horse type stance, the ears will be very erect and immobile, flared nostrils, the third eye lids may protrude, the jaw will not open, hence the old name of “Lock Jaw”, and the tail will often be held straight out behind the patient. The affected individual may be hypersensitive to noise, with its muscles going into spasm at a loud sound. As the disease progresses the patient ends up lying down and eventually the respiratory muscles become paralysed which results in death.

The signs of tetanus can occur 7-21 days after the penetrating wound. Death usually follows within 7-10 days.

Foals are particularly susceptible to tetanus, the navel is a site at which contamination with the Clostridium bug can occur. This is why it is important to have a foaling box that is as clean and hygienic as possible prior to foaling, the navel should quickly be treated with a topical antibiotic spray and a tetanus antitoxin should be given within the first 24 hours of life. Mares around the time of foaling may also be injured internally and may become affected by tetanus. Simply vaccinating the mare a month prior to foaling will boost her own antibodies and will also boost the level of antibodies within the colostrum that the foal should receive from its mother in the first 12 to 24 hours of life.

If a wound is detected on a horse it is always important to clean it thoroughly, even clip any long hair away from the edges so that the nature of the wound can be investigated properly. A cold hose is a good way of rinsing contamination out of wounds. Hoof wounds can be lavaged with a hydrogen peroxide solution. If there is any doubt about the character of a wound and the vaccination status of the patient, then veterinary attention should be sought.

If a horse, pony or donkey is thought to have tetanus, treatment can be attempted - the wound in question would be surgically debrided, opened up to allow oxygen in and lavaged to remove contamination. A tetanus antitoxin can be administered in massive doses to neutralise the neurotoxins and antibiotics such as penicillin will be used to kill the bacteria. Other than this it is a case of nursing the patient in a cool, dark, quiet space; usually intravenous fluids are given to maintain hydration status. Sedatives and muscle relaxants can be used to control the muscle spasm. Often the bladder and rectum do not work properly so it may be necessary to catheterise the bladder so it can be emptied and also to empty the rectum manually. Some patients may survive, but sadly very few.

Vaccination is a very effective way of preventing tetanus. Ideally the first vaccine for tetanus should be given to foals at about 3 months of age, when the antibodies that the foal has acquired from its mother in the colostrum have diminished. However, mostly foals are first vaccinated for tetanus in combination with influenza vaccine at about 7 months of age, when the maternal antibodies for flu have gone. A second vaccine is then given approximately a month later (21-92 days later in combination with the second flu vaccine). Once a horse has had 2 vaccines it should really be adequately protected within 2 or 3 weeks of the second vaccine.

Vaccination is then usually repeated with the third flu vaccine of the course within the period 150 to 215 days after the second vaccine of the primary course. The vaccine can then be repeated at the first annual booster for flu (within 365 days of the third vaccine), thereafter vaccination is only necessary for tetanus every 2 years. The exception to this is mares that are in foal and these are usually vaccinated every year prior to foaling for both flu and tetanus.

Any horse (including foals) that has not had a correct course of tetanus vaccine should be given a dose of tetanus antitoxin if a wound or foot abscess is identified.

Dr Ed Lyall, BVetMed, CertEM (StudMed), MRCVS

Poor Performance

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Joint Disease as a Cause of Poor Performance

 Once a joint has been identified as a problem, the next step is to investigate that joint further to see if there is a major bone problem or whether it is a simple synovitis from a joint sprain. Radiographs of the joint can be very helpful. Often now, a set of radiographs is obtained when a horse starts out on its sporting career as these act as useful reference images if there are problems in the future.

The images may show problems in a joint that would direct us to investigate the joint further. This can be done by performing a bone scan to look at bone turnover associated with margins of the joint, which may help in identifying cracks or stress fractures in the bones adjacent to and thus involving the joint. Bone scans can also be helpful in older horses to investigate problems such as with the hock joint.

MRI is an important way of investigating joints, particularly in the distal limb and hoof regions. A horse that goes sound by blocking the coffin joint may actually have a problem with one or more of the complex ligamentous or tendinous structures, such as the collateral ligaments or the insertion of the deep digital flexor tendon. By correctly identifying the problem, correct therapy and management can be instituted.

Some joints will be investigated surgically using a procedure called arthroscopy. A camera is placed through a keyhole incision into the joint so the articular cartilage within the joint as well as the synovial lining of the joint and any visible ligaments can be assessed. The advantage of this investigative procedure is that any cartilage problems identified can be surgically curetted at the time. Few sport horse joints would need surgery; however in an older horse that is having continued problems with a specific joint, it would be better to operate sooner rather than later. Ultrasound can be used to assess the articular cartilage within some joints, and also the ligaments around the joints. Most of the time when there is a problem with a joint, a simple block to confirm which joint and a few x-rays will suffice.

Wet Winter Problems

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Thrush is an infection of the horses frog resulting from poor foot hygiene and prolonged exposure to wet conditions These infections most often involve the bacteria Fusobacterium necrophorum and occur in the central and lateral sulcus (clefts or grooves) of the frog.. Thrush appears as a black, foul smelling discharge from the central or lateral sulci of the frog. Affecting either hind or front feet, deep narrow clefts predispose to thrush more than normal. Discharge from the affected area is variable and may not be noticed unless the sulcus is closely examined and cleaned out. In more advanced cases the frog and sole tissue can become under-mined or under-run. Infection of the deeper more sensitive tissues and exposure of sensitive corium can cause lameness and may lead to a secondary cellulitis and swelling of the lower limb.

THRUSH

Often horses with contracted heels and atrophied or weak and narrow frogs are more susceptible due to the depth of the sulci and similarly, horses with overgrown hooves are more prone to the problem.

Prevention is better than cure and thrush can be prevented with good stable management, cleaning and inspection of your horse’s frog. Additionally, providing clean, dry bedding for horses is vital, as horses that live in a wet, muddy or dirty environment are more susceptible to infection. Exercise helps to maintain healthy blood flow to all regions of the foot and helps to maintain a healthy frog with normal hoof architecture. One of the most important and basic steps to take to prevent this is to pick your horse’s feet out at least twice a day.

Treatment of early, mild cases involves debridement of affected tissue and sometimes topical treatment with iodine or hydrogen peroxide. Affected horses should be kept on a clean dry bed. More serious cases may require a more extensive debridement, antibiotic therapy and therapeutic shoeing that protects the affected area whilst it heals.

MUD FEVER

Mud fever, also known as pastern dermatitis, is another aliment arising from wet weather conditions. It is caused by a combination of different factors including skin irritation, bacteria, and moisture. The equine skin has a normal balance of bacteria on the surface however if the skin is wet for prolong periods of time the skin softens and the bacterial population change and become unbalanced, these then multiply in the damp warm environment and can lead to infection and mud fever.

Factors predisposing to mud fever include: long periods of damp and standing in wet environments, washing and scrubbing legs that causes abrasions and if not dried properly leads to a damp environment, feathers and cob types as these are harder to dry properly and also may have chorioptic mites that will break the skin allowing bacteria to enter.

Prevention (which is better) and treatment is based on keeping the skin dry and clean. If a horse does have or is prone to mud fever, it may require stabling until the horse can recover and maintain a healthy skin surface. Gentle cleaning with chlorhexidine, iodine or medicated shampoos can help re-establish a healthy population of normal skin bacteria, but you must rinse and dry them properly afterwards. Over washing or vigorous scrubbing will traumatise the skin surface and can lead to mud fever, so be conservative. If your horse has a scab, do not pick them unless they are soft and ready to fall off, picking scabs breaks the skin barrier and allows the bacteria to enter the skin again. There are many topical treatments that soften scabs whilst bathing the skin in anti inflammatories. If keeping your horse in a dry stable is not feasible then you can apply a barrier cream to the leg, these creams are designed to repel the water away, keeping the leg dry. Bandaging is also an effective way of keeping the leg dry but you must ensure the bandages do not get wet on the inside and do not rub. Sand schools or sandy soils are particularly abrasive to the skin so washing legs after exercise or turn out is important but be gentle! Proper pasture management to avoid mud pits will also help prevent mud fever.

Sometimes a mud fever infection can lead to cellulitis, when the leg swells and the swelling travels up the leg or a hot painful pitting oedema develops, it is likely your horse has cellulitis. Cellulitis will require veterinary care as horses should be assed and possibly prescribed anti-inflammatories and antibiotics to help your horse fight the infection.

Dr. C. Baldwin, BVetMed, MRCVS

Welcome New Directors

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Congratulations to Three New Directors - Paula Broadhurst, Andy Crawford and Simon Staempfli have joined Ed Lyall, Matt Waterhouse and Rob Van Pelt in becoming directors of the Arundel Equine Hospital this month. This exciting news means that we have guaranteed that the future of the practice will be in safe hands for many years to come. The three new directors will now assist in the day to day running of the ever growing practice, as well as dealing with their clinical case load. Paula has in fact made history in that she is the very first lady director (partner) that the practice has ever had!

“Tying Up”

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‘Tying up’, also known as Azoturia, Monday Mornings Disease or Recurrent Exertional Rhabdomyolysis (RER) is the most common muscle disorder in horses, frequently limiting performance in sport horses of varying breeds. Tying-up is basically muscle cramps, the largest muscles in the horse (back and hindquarters) are most often affected by a combination of different (it is not fully understood) mechanisms, leading to a buildup of lack of muscle oxygenation, lactic acid and muscle cell death.

‘Tying-up’ usually affects horses in a high level of work that are rested for 1 or more days and still fed a high carbohydrate:low fat diet. It most often occurs after 20-30 mins of work during the first exercise following a period of rest. However, it may also occur as a result of increasing intensity of work or unfit horses undergoing prolonged periods of exercise. Any breed of horse can be affected. It most often occurs amongst younger horses and affects mares more than males. Some horses experience only one or two isolated cases, whilst others suffer repeat episodes which subsequently limits their athletic potential.

Stress, excessive sweating, lack of drinking before and after work or not travelling well will cause electrolyte imbalances or disturbances which predispose a horse to ‘tying-up’. As can a diet high in cereals (as these contain a high potassium:sodium ratio) or deficient in certain minerals and vitamins. Some blood lines are also prone to producing horses that regularly ‘tie-up’ so there is a suspected genetic component too.

Depending on the severity of the episode, horses will demonstrate varying clinical signs from a mild discomfort and stiff gait to a very stiff gait and refusal to move or even in severe cases recumbency due to the pain. Most horses will have firm painful muscles in the gluteal, hamstring and back area, some horses will develop muscle swelling. Tying up is very painful and horses may become distressed and anxious, they may increase their respiratory rate, sweat or even show colic like behaviour.

If you are out riding away from your horse’s stable and your horse ‘ties-up’, phone for help. The horse should be transported by lorry or trailer to limit any further muscle damage. Once the horse is in a stable, keep them warm with plenty of rugs and offer water.

Diagnosis is made based on clinical signs and a blood test measuring muscle enzymes and kidney parameters. The enzymes are released from inside muscle cells when they are damaged. Myoglobin is a product also released by damaged muscle cells. This can discolour the urine brown or orange, potentially causing kidney damage if severe enough.

Immediate treatment depends on the severity of the episode but the aim is to provide pain relief, reduce further muscle damage and protect the kidneys. If mild; encourage the horse to drink (restoring electrolyte balance) and if the horse is comfortable you can walk them around to stop them stiffening up further, but do this with caution! If the horse is very painful, reluctant to move or recumbent, do not try to move the horse! This may lead to further muscle damage. Call your vet and allow them to provide pain relief and anti-inflammatories. The vet may also give acepromazine (ACP), a drug that calms the horse down and causes the blood vessels to dilate, increasing blood supply to the muscles. If the horse is dehydrated there is a risk of kidney damage so the horse may require rehydration by oral fluids or intravenous (IV) fluids. Other drugs are available to help stabilise the muscles and protect from further damage.

Prevention is better than cure and so if you have a horse prone to tying up it is important to provide a high-fat (bran and oils), low-carbohydrate (grains) diet, ensure your horse is properly warmed up and cooled down before and after work and exercise the horse every day, as one or more days of inactivity seems to preclude ERE episodes.

Vitamin E and selenium supplements can also be of benefit, as can antioxidants and other drugs and herbal supplements which your vet can inform you about.

Some horses suffer from chronic ER, these horses require further investigations to define why they continue to ‘tie-up’, this can involve repeat blood tests, exercise tolerance tests, and muscle biopsies.

Chris Baldwin, BVetMed, MRCVS

Sacroiliac Joint

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Sacroiliac pain in horses is a performance limiting condition that can be challenging to diagnose and manage. To understand why horses develop this problem we first need to understand the anatomy involved.

The pelvis is a ring of bones formed of three fused bones; Ilium, ischium and pubis. The lower part of the horses back, the sacrum, is formed of 5 fused vertebrae. The sacroiliac joint (SI) is the joint where the sacrum passes underneath the top of the pelvis (tubera sacrale). The SI joint is strengthened by the ligaments; dorsal, ventral and interosseous sacroiliac ligaments. SI pain is either in-flammation of the joint or ligaments surrounding the joint. The SI joint functions to transfer propulsion from the hindlimbs to the spine, supporting the horses back and driving the horse forward from its hindquarters when in motion.

SI pain typically affects heavier, taller horses usually between the ages of 5 and 15 years old. There is no documented association between a horse’s confirmation and developing SI problems. Warmbloods, Thoroughbreds and Thoroughbred crosses are over represented, as are horses used for show jumping and dressage, which may be due to athletic demands placed on these horses during their work.

The signs that a horse maybe suffering from SI pain are subtle and insidious in onset and progression. Typically the signs are exacerbated when the horse is ridden under-saddle and can be easier to appreciate by the rider than to be seen by an observer. There may be no overt lameness to be seen. Table 1 lists the common signs of SI pain.

 

Common complaints related to SI pain

 

* Poor performance / unwillingness to work / holding back

 

* Lack of impulsion or animation 

 

* Intermittent lameness

 

* Reluctance to be shod or have the leg held in a flexed position for a prolonged period of time

 

* Poor or stilted canter, becoming disunited, taking the wrong lead leg

 

* Stiff through the back, refusing jumps

 

* Poor lateral work

 

* Change in behaviour or performance when worked on the bit

 

Diagnosis is challenging due to the mass of muscles surrounding the SI joint. A thorough physical exam by a veterinarian is required to rule out other conditions. SI pain is a consequence of a change in the mechanics of the horse’s back and hindlimbs. Therefore conditions such as suspensory ligament desmitis or kissing spines (impinging spinous processes) can be a precursor or sequel to SI pain.

Xray and ultrasound of the SI region is limited due to the anatomy. The most sensitive form of diagnosis is a bone scan (nuclear scintigraphy). The SI joint can also be anaesthetised (blocked) and if there is pain at this site an improvement maybe seen or felt.

Treatment of SI pain requires a combination of medication, physiotherapy and a rehabilitation programme. The SI region can be injected with steroids to reduced inflammation of the joint and ligaments. This will be performed by your veterinarian when required and usually requires more than one treatment. Physiotherapy and rehabilitation are important in making sure the horse works to build up strong muscles around its hind quarters so the SI region is protected and used correctly. Each horse with a diagnosed SI condition will have a tailored rehabilitation program outlining the details of exercises and time period. In feed, anti-inflammatories or joint supplements may be beneficial in reducing in-flammation and promoting healthy joints. Other treatments such as acupuncture or magnetic rugs/boots, may be of benefit however there is little published evidence supporting this.

In summary, the SI is the connection point between the horse and its hindlimbs. The condition mainly affects larger horses undertaking dressage and Show jumping. the signs of SI pain are very subtle. Diagnosis is challenging and treatment involves a combination of medication and rehabilitation.

Chris Baldwin, BVetMed, MRCVS

Atypical Myopathy

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Atypical Myopathy was first recognised back in 1984 but has largely come to prominence over the last few years with outbreaks in the UK and Europe. It occurs in individuals or groups of horses at pasture and is likely caused by ingestion of seeds known as ‘helicopters’ (and possibly to a lesser extent leaves) of the sycamore tree (Acer Pseudoplatanus) that contain a specific toxin. This toxin has been identified as hypoglycin A. The amount of toxin within seeds is variable and it is not understood why some seeds have more toxin than others nor is it understood how many seeds have to be eaten for a horse to become sick. It is likely that some horses will be more susceptible than others with younger horses appearing particularly susceptible, particularly those in poor bodily condition, on relatively poor quality pasture. As older horses are less likely to become affected it may be that they develop some tolerance to the toxin.

Incidences tend to occur in the autumn and in the spring following large autumnal outbreaks and are often following a sudden adverse change in weather conditions, such as a frost or heavy rain. 

It can cause a variety of clinical signs which can present as dullness or lethargy or as a sudden onset of muscle stiffness or weakness that can progress rapidly to recumbency. Other reported signs also include reluctance to work, choke, whinnying, head tossing or an abnormally low head carriage. It can affect the diaphragm resulting in difficult or laboured breathing and some cases may show some colic like symptoms such as paddling or stretching the limbs. Due to the breakdown of the muscle urine often appears dark red and brown. If it affects the heart muscle it can result in a fast or irregular heart beat and in the worst case some horses may present as a sudden death. The mortality rates vary from 40-100% and vary from year to year.

DIAGNOSIS

Diagnosis is based on clinical signs alongside an increase in serum muscle enzymes (AST/CK) and the presence of red/brown urine.

TREATMENT

Prompt diagnosis and treatment is essential if horses are to have any chance of survival. There is no specific treatment only supportive care which involves hospitalisation, intensive intravenous fluid therapy and nursing. Fluids are required to provide cardiovascular support as horses can become very dehydrated and to support the kidneys as the product of muscle breakdown (myoglobin) can affect their function and can cause renal failure. If there is concern over the kidney function then they may also be given a diuretic to help the kidneys maintain a good urine output. This condition can be extremely painful and so a variety of powerful painkillers and anti-inflammatories may be required. When horses become recumbent then they require frequent turning to encourage them to stand and to prevent sores. If they are inappetant then they are provided with an alternative source of nutrition usually by stomach tube in order to provide their energy requirements. Supplementary vitamins and minerals have also been shown to be useful in some cases.

Prognostic factors for survival are normal mucosae, no respiratory distress signs, a standing position most of the time, no temperature, and normal abdominal transit.
Factors unfavourable to a recovery include recumbency, abundant sedation, anorexia, tachycardia (a high heart rate), tachypnoea (high respiratory rate), respiratory difficulties and severe acid-base disturbances. Euthanasia may have to be considered when horses appear to have reached the stage where they are no longer likely to respond to supportive treatment.

In horses that do recover, recovery is initially slow, but most go on to make a complete recovery and return to work with no long-term effects of the disease.

PREVENTION

Given the high mortality rate prevention is better than cure. If sycamore seeds are present in your fields then the following is advised

- Avoid letting horses graze pasture that are contaminated with the sycamore seeds. 
- Move horses out of the field to as distant a point as is practical, or stable the horses during the risk period. 
- If you are unable to remove horses from pastures then fence off areas where the seeds and leaves have fallen and offer supplementary hay but do not leave it on the ground to get wet and feed extra concentrate.
- Rake up or hoover and remove the seeds, dead leaves and saplings where possible.
- Reducing the stocking density can help to ensure there is good grazing for every horse.
- If you are suspicious that your horse may have ingested some of these seeds then call your vet out to check the muscle enzyme levels (AST/CK) to identify subclinical and pre-clinical cases.

If you suspect that your horse is showing any signs of atypical myopathy then contact your vet IMMEDIATELY. If you have any other concerns then please do not hesitate to contact your vet practice for further advice.

Images of Sycamore trees and seeds.