Presented at Equitana 2003
by Dr Pat Harris PhD VetMB MRCVS,
Equine Studies Group, WALTHAM Centre for Pet Nutrition and WINERGY®
It is a cold spring morning and after a weekend away you decide to fit in an early morning ride — because of time pressures you press on quickly and then suddenly your horse seems reluctant to move forward, starts to take stiff short strides and comes to a halt — sweating perhaps more than normal — is this disobedience or is something wrong?
For those of you who have ever had a horse that suffers from Tying Up or the Equine Rhabdomyolysis Syndrome the above scenario or a variant (as the background to an episode varies from case to case) may be distressingly familiar. Unfortunately despite progress in our understanding of this condition it still remains a major problem for many horses and their owners. However, there is some light at the end of the tunnel. This condition has in fact been recognised, under various names, for well over a century (Key Facts 1). Although horses dying from the condition are now relatively rare, the incidence of more mild episodes seems to be increasing. This may reflect our increased awareness of the condition or it could be linked with the way we currently manage and feed our horses.
Who can be affected?
This condition can affect any type of horse regardless of its breed, value, age or sex. There does seem to be an increased risk, particularly in some breeds, in the mare and particularly the young filly.
What are the clinical signs?
This condition affects the muscles of horses so that they cannot function as normal and therefore results in the partial or complete inability to move. This results in a wide range of possible signs from a show pony that may fail to lengthen when asked, or a race horse that slows in the closing stages of a race, to the more typical animal that is unwilling or cannot move, or more rarely an animal that actually goes down and cannot get back up. The more typical stiff or immobile horses are easier to recognise as potential sufferers from this condition.
Signs tend to become obvious during exercise but exactly when during an episode bout an attack occurs and how severe it is varies between horses and even within the same individual on different occasions. The time period between episodes also varies (from days to months), although the initial return to work from an episode tends to be the most vulnerable period for a repeat episode. It is usually impossible to visually determine that any particular animal is prone to this condition, as susceptible animals tend to look and act normally between episodes.
During an episode the affected animal will often be in some pain and distress although this tends to vary with the individual and the extent of the damage. Typically the muscles of the hind limbs are the most severely affected but in a few individuals the forelimbs may also be involved. Muscles may be swollen and/or painful to touch but this is not always the case, especially in the more mild cases. The affected area is normally quite generalised over one or more muscle groups compared with the more localised pain that may result from pulled or strained muscles.
What causes it?
Most sufferers tend to have an underlying susceptibility to the condition, which may then be triggered by one or more factors, usually including exercise, resulting under certain circumstances in the clinical signs.
The underlying factor or factor(s), as well as the triggering factors differ between groups of sufferers — so the measures that may be successful for one horse may not be so successful in another. Two distinct subgroups (and there are likely to be others), with specific and different causes, have been discovered in the last 10 years. One involves a disorder in muscle contractility (seen especially in young Thoroughbred fillies in training: see Key Facts 2) and the other involves a defect in sugar/carbohydrate storage and/or utilisation (polysaccharide storage myopathy: PSSM; found especially in Quarter horses and related breeds. See Key Facts 3).
Diagnosis and Treatment
It is important to realise that in some cases an episode may have been triggered by a whole host of unfortunate one off factors that will never happen again and therefore once back in work the horse may never suffer another episode in its life. Other horses seem to continually suffer from this condition despite the best efforts of all concerned. Certainly it is important not to assume that a horse which, has had one ‘full’ confirmed episode, is suffering from this condition every time it goes a bit ‘stiff’. However, a true recurrent sufferer is unfortunately likely to suffer further episodes — certainly if the management changes suggested here are not followed — and sometimes even if they are.
A provisional diagnosis is therefore usually based on the clinical history plus the clinical signs and may be then be confirmed by monitoring plasma muscle enzyme activities (Creatine Kinase: CK and Aspartate Amino Transferase: AST) and in the case of PSSM by means of a muscle biopsy. As described above because the clinical signs can be so variable, the condition can be relatively easy or difficult to diagnose.
Veterinary treatment may be required, depending on the clinical severity. This aims to limit further muscle damage, decrease any pain and anxiety, and most importantly restore the fluid balance plus maximise the chance of a speedy return to work. Monitoring before and during the return to work, by means of blood tests, can be of value especially for the animal that repeatedly suffers episodes (exercise associated samples need to be taken before and approximately 2–6 hours after the current exercise regimen for AST and CK activities).
Some practical tips on what to do if your horse has an episode are given in Key Facts 4.
How can it be prevented?
Unfortunately there is no single procedure or set of procedures (including diet and management) that can guarantee against further episodes. However, appropriate management procedures and nutrition of susceptible animals may help to reduce the likelihood or frequency of future episodes.
For some susceptible animals ‘stress’ may be a contributing triggering factor. Therefore wherever possible the level of ‘stress’ experienced should be kept to a minimum e.g.:
- If they are quieter being ridden out in company then ride out in company or vica versa. If they get disturbed around feed time then feed them first.
- Keep to the established routine as far as possible.
If certain trigger factors (such as not reducing feed on days of rest; prolonged periods of stable rest; overexertion, being in season, using the horse walker, restraining from reaching top speed when galloping, etc.) can be linked to episodes then these trigger factors should be avoided wherever possible. It is therefore helpful for owners of animals that do suffer from repeated attacks to keep a good record of events.
The actual diet which will be the most beneficial to a sufferer will depend on the horse as an individual, and what they are being used for (as this influences the energy needs), as well as their history with respect to Tying up. There are, however, some general principles that should be followed:
- Firstly, the major proportion, if not all, of the daily intake of feed should be forage — either fresh (pasture) or preserved (grass hay or hay equivalents). See Key Facts 5.
- If the horse’s energy needs cannot be met by forage alone then it will be important to provide in addition some form of supplementary feed. See Key Facts 6.
Salt should be provided, for all horses (Key Facts 7). Over the past few years the author has been able to either reduce the frequency of episodes or to prevent further episodes in a number of recurrent sufferers by appropriate electrolyte (calcium, magnesium, sodium and potassium) supplementation. It is therefore important to try and ensure that the core diet provides a sufficient intake of these electrolytes in an adequate and balanced manner. In recurrent cases it may be worth determining individual requirements by means of the Fractional Electrolyte Excretion Test, which involves the collection and analysis of blood and urine in collaboration with your Veterinary Surgeon.
The selenium containing enzyme, glutathione peroxidase and Vitamin E help to protect against free radical induced cellular damage (oxidative damage). These are therefore important antioxidant nutrients for all horses regardless of whether they suffer from this condition or not. It is unlikely that Vitamin E/Selenium deficiency is the primary cause in the majority of cases. However, in certain individuals a concurrent Vitamin E/Selenium deficiency may be a contributing or a permissive factor in the syndrome. It is therefore advisable to ensure that all horses, but in particular those susceptible to this syndrome, are fed adequate Vitamin E and Selenium. The author’s recommended levels are Vitamin E at 160iu/kg DM intake plus additional Vitamin E to support any supplemental oil (see Key Facts 8); Selenium at 0.2mg/kg DM intake.
Unfortunately we are still ‘tied up’ in the 21st century but increased awareness of this syndrome, and the ways that the risk of an episode can be reduced will hopefully help to reduce the incidence of this distressing condition.
Key Facts 1: History of Monday Morning Disease, Azoturia, Tying up, Equine Rhabdomyolysis Syndrome
In the 19th and early 20th century draught horses often did not work on Sundays — unfortunately their feed (often heavily cereal based) was not reduced in line with the work load. Occasionally as they worked on the Monday they would collapse with severe muscle damage and on occasions actually die — this was commonly referred to as Monday Morning Disease. As awareness increased of the links between nutrition, feeding practices and disease this form of the condition became less common. In the 1930s Azoturia (named because products of protein breakdown were found in the urine of cases) was actually reproduced by feeding very large amounts of molasses and then exercising. The theory being that excessive muscle glycogen (a storage form of glucose) was deposited during periods of rest which was quickly converted to excessive lactic acid during exercise — effectively ‘poisoning’ the muscle cells.
By the time I started to work, in the mid 1980s, on the more typically milder form of the condition ‘tying up’ (named after the most common clinical sign: an inability to move) this theory was out of favour because most horses that suffered from this condition did not have higher levels of lactic acid in their plasma or muscle than non-affected similarly exercised horses. I refer to it now as the Equine Rhabdomyolysis (means inflammation of the muscles) Syndrome, as this condition is multifactorial and can occur in horses that have not been exerted. Other common terms used today are Exertional myopathy or Recurrent Exertional Rhabdomyolysis.
Key Facts 2: Recurrent Exertional Rhabdomyolysis
- Due to an abnormality in the process of muscle contraction.
- Found mainly in Thoroughbreds, Standardbreds plus Arabians and especially in the young nervous filly in training.
- Affected animals often experience very frequent episodes with persistent AST elevations and often are retired early from training.
- Triggering factors appear to be training at a gallop but restraining the horse from reaching top-speed, prolonged periods of box rest, high grain diets, excitement and the presence of a concurrent lameness.
- May be an inherited condition.
- Confirmation of the diagnosis involves whole intercostal muscle biopsies and intensive laboratory tests and therefore is rarely undertaken.
Key Facts 3: Polysaccharide Storage Myopathy (PSSM)
- Caused by a defect in the way that glucose is handled and stored in the muscle.
- Affected animals have high levels of glycogen (a normal storage form of glucose) and a non-available abnormal glucose storage compound (a polysaccharide) in their muscle.
- The levels of glycogen can be up to 4 times that of normal horses.
- Mainly found in Quarter horses and related breeds, Warmbloods and a few Arabians, Standardbreds and Thoroughbreds.
- Draught horses and Warmbloods appear to suffer from a related condition with slightly modified clinical signs.
- In Quarter horses and related breeds there appears to be a hereditary basis for PSSM.
- Trigger factors include being rested for a few days prior to exercise, infection and most importantly the diet.
- Horses tend to have a more calm temperament than the other subgroup and often have persistent elevations of CK without these always being associated with clinical signs.
- On biopsy the muscle fibres have large amounts of the polysaccharide that cannot be digested by amylase (unlike ‘normal’ glycogen).
Key facts 4: Practical tips for managing a horse with tying up
Always contact your Vet for advice. However these are some practical tips.
- Avoid forced walking and if possible get the Vet to treat the horse where it has suffered the episode.
- In the more severe cases if transportation is needed then ideally a truck, rather than a float, (providing the ramp is not too steep) should be used.
- Regardless of the mode of transport the horse must be safely supported, throughout transportation, in such a way that further muscular effort is kept to a minimum.
- Put in a clean dry stable (so that you can tell that urination has occurred), away from draughts.
- Provide grass hay and if necessary later on a small meal of a high fibre pellet — which can be soaked so that it forms a moist gruel.
Proceed to the next stage when:
- The affected animal has been moving freely around the stable for several hours.
- There are no signs of pain when the muscles are felt and the horse does not resent (anymore than normal) any palpation.
- The urine is not discoloured by myoglobin (a reddish brown pigmenting protein released from damaged muscle).
If in doubt about when to proceed, contact your Vet.
- Turn out into a small paddock (rather than start in-hand or ridden exercise) but avoid ‘lush’ pastures (treat in a similar way to a laminitic) or getting ‘cold’.
- Encourage ‘gentle’ movement in the paddock (e.g. turn out with a quiet known companion — put the feed and water at opposite ends of the area etc).
- If your horse is very excitable it may be worth discussing this first with your Vet (although it is rare that sedation is needed).
Starting to ride again
- In mild cases you can start after only 2–3 days in the paddock unless directed otherwise by your Vet. In more severe, or repeat cases, wait until the muscle enzyme activities have returned to within acceptable limits.
- Especially in the initial stages of a return to work avoid lunging, horse walkers, or work in tight circles, as well as hill work.
- Slowly increase the intensity and duration of the exercise and if your horse misbehaves on its own or in company, ride alone or with others as appropriate
- Daily exercise or turnout often seems to be valuable — but again avoid ‘lush’ pastures.
- Decrease the work intensity and concentrate feed intake if there is any suspicion of a respiratory viral infection being present on the yard.
- Continue to avoid pastures that may have high water-soluble carbohydrate or Fructan content (treat as if a laminitic).
When in work again/General advice
- Keep to regular daily exercise.
- Avoid the use of horse walkers.
- If daily exercise is not possible turn out for as long as possible on rest days and reduce any complementary feed intake (half) from the evening before the day of rest and do not start to increase back to normal until the evening afterwards.
- If a more prolonged period of rest is to be given then the type of feed fed should be evaluated and either one of a lower energy density, or forage alone, appropriately supplemented, should be fed.
Key Facts 5: Forage
- For the majority of horses it is preferable not to feed large quantities of lucerne or other legume rich hays (but remember to ensure that the overall diet is balanced with respect to minerals including Calcium).
- Small amounts of lucerne chaff fed in increasing amounts, in conjunction with increasing workload, may be a beneficial addition especially for those horses in hard work or those in which a calcium imbalance may be present (suggested by an urinary Fractional Electrolyte excretion test).
- If the energy needs of the individual horse can be met by forage alone — i.e. the horse maintains the desired body condition and provides you, the rider, with the type of ride you require then they should be fed ~ 100% forage.
- An appropriate general vitamin and mineral supplement normally, however, will be required to ensure appropriate overall nutrition.
- Do not turn the horse out onto lush fast growing pastures but prolonged daily periods out in a sparse paddock is often beneficial.
- Other fibre sources may be fed if required, in addition, to ‘straight’ forage. Good alternatives, in particular for those animals that need more energy than the forage alone can provide, include unmollassed soaked sugar beet pulp appropriately prepared and Soya hulls.
Key Facts 6: Supplementary Feed
- A fibre based, low starch, complementary manufactured feed (i.e. high fibre, low cereal — especially a low oat — feed).
- If more feed than recommended is needed to maintain condition or provide the type of ride required, consider adding additional supplementary oil — see Key Facts 8.
- If the amount of manufactured feed that is needed to be fed, to enable the horse’s desired body condition to be maintained and you to have the type of ride you prefer, is less than the manufacturer’s recommendation for that work load then an appropriate vitamin and mineral supplement should be provided. Usually it is helpful to contact the Nutritional Helpline of the complementary feed being fed and inform them of the diet, workload and get direct advice appropriate for their feed.
- Or Supplementary oil fed in addition to short chopped forage or chaff and an appropriate vitamin and mineral supplement.
- Avoid the addition of wheat bran to the horse’s diet — wherever possible but certainly avoid large amounts (imbalanced calcium to phosphorus ratio).
- Do not feed in anticipation of an increase in workload — wait until additional energy is needed before the intake is increased.
- It has been recommended that horses suffering from PSSM are not fed any cereal starch at all and that their sugar intake in general is kept as low as possible.
- It has been recommended that race horses, especially those suffering from the excitation-contraction form of this syndrome, are not fed more than 2.2kg of a cereal based coarse mix /grain per day.
Key Facts 7: Salt
- Salt should be provided, for all horses.
- For those horses in little or no work the provision of a salt block or free choice salt may be adequate (but ensure that it is sited so that its use by that individual horse can be monitored). Where complementary feed or a vitamin mineral supplement is being fed, any block should be a pure salt rather than a mineralised one.
- It is not advised that blocks formulated for other species are used.
- For those horses in more work or who sweat noticeably the recommendation is that additional salt should be added to the feed.
- As a very practical guide: For a 500kg horse the amount could start at about 14g/day and build up to around 56g/day depending on the time of year, work load, and sweating rate. If, when the additional salt is fed, the horse either will not eat the feed (and providing it is not a fussy feeder!) or obviously urinates more than normal it may be helpful to reduce the amount by 14g, leave it at this level for a few days, monitor and reassess.
Key Facts 8: Feeding Supplementary Oil
Supplementary fat or oil can be supplied in three main ways:
- High fat feeds — such as rice bran (which is also high in fibre and usually low in starch). However, many of the rice brans available have the same disadvantages of wheat bran in that they have very imbalanced Calcium to Phosphorus content which may be potentially detrimental. If a manufactured high oil feed is used, it must be a high oil, low starch, high fibre feed.
- Animal fat — many horses find most animal fats to be unpalatable and they seem often to be more likely to cause digestive upsets. There use is not to be recommended.
- Vegetable oils — such as fresh corn oil or Soya oil — preferably human grade, palatable and digestible to your horse.
- Any supplemental oil or high oil-containing product should be introduced slowly.
- Adding oil to existing feed has the potential to create multiple imbalances and where possible a fortified manufactured high oil, low starch, high fibre diet is preferred.
- As a guide do not feed more than 100g oil/100kg BW/day in divided doses — provided that it has been introduced gradually, is required and is not rancid (and the Vitamin E levels are considered see below). NB Not all horses will require such amounts.
- In order to obtain metabolic benefits from the feeding of oil, in addition to those associated with its high energy density and lack of starch content, the oil needs to be fed for several months.
- It is very important to note that oil does not provide any additional protein, vitamins or minerals (and the Vitamin E content is variable). If the horse is not receiving sufficient, for its workload, from its basal diet, then an appropriate additional mix may be needed (usually it is helpful to contact the Nutritional Helpline of the feed being fed and inform them of the diet, and workload and get direct advice appropriate for their supplement).
- It is recommended that additional Vitamin E be fed in combination with supplemental oil. Exact recommendations are not known but an additional 100iu Vitamin E/100mls added supplemental oil is the author’s current recommendation
For further nutritional advice visit WINERGY.