All Tied-Up

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RER, PSSM, Azoturia, Monday Morning Disease, Set-Fast...if your horse is prone, it might be worth checking what you’re feeding

Muscle problems have previously had a variety of different names such as Monday Morning Disease, Setfast and tying-up, that have described the symptoms rather than the disease. Advances in research have resulted in a better understanding of the disorders and therefore more appropriate names have been introduced. Two distinct disease processes have been identified with each one seeming to be prevalent in certain breeds, suggesting that a genetic factor is likely to be involved.

Trigger Factors

One of the questions that frustrates owners of horses that suffer with these problems is why does it happen one day and not the next? Very often there is no obvious reason why the problem occurred on any given day but in some cases it can be that a number of trigger factors all coincided sufficiently to tip the balance. Possible trigger factors include not reducing the feed prior to a day off, not warming-up or cooling down properly, high starch diets, dehydration/fatigue and viral infections. On their own, the horse can often tolerate one or other of these factors but when several combine, problems can occur.


The degree of severity of the symptoms can vary enormously from a horse that appears slightly stiff but is still able to work to some degree to a complete seizing of the muscles so that the horse can’t move. If the symptoms are only very slight then it is very difficult to diagnose the problem as there could be several other causes. It is important when seeking advice from a vet or nutritionist that you give details of when the problem occurred i.e. was it before, during or after the horse had worked, and as many details about the horse’s regime that day as possible as this will help them to advise you on a suitable diet.


  • Quarter horses, Warmbloods and draught horses are most commonly affected
  • Typically, quiet laid back animals but with no gender bias
  • Prevents normal metabolism of glycogen which is how the horse stores starch and sugars in his muscles


  • Eliminate cereal grains and molasses from the diet
  • Use oil and fibre as energy sources according to the horse’s bodyweight and workload
  • Provide a balance of vitamins, minerals and protein

How to achieve this:

Step 1 – Feed plenty of forage

Forage should form the basis of all horse’s diets but is particularly important in horses that cannot tolerate large amounts of grain. Select as good a forage as possible as this will provide more energy and nutrients which will help to meet the horses overall requirements. Alfalfa Blend or Alfalfa Plus Oil  can be fed to provide more digestible fibre and nutrients than the same weight of hay would provide.

Step 2 – Select a balancer

Lo-Cal balancer for horses in light to moderate work or Performance Balancer for horses and ponies in moderate to hard work. These will provide the nutrients required to maintain health and condition and for work.

Step 3 – Add oil or highly digestible fibre

Outshine is a high oil supplement that can be fed alongside a balancer and provides a concentrated source of slow release calories. Outshine also contains additional vitamins and minerals, such as selenium and vitamin E, which are vital for protecting the muscle cells and so is preferable to just adding straight oil. Sources of highly digestible fibre, like Speedi-Beet or Fibre-Beet, are also useful as are Alfalfa Blend and Alfalfa Plus Oil.

For horses in up to moderate work, Keep Calm is a fully balanced option which is based on Speedi-Beet and contains just 7% starch.


  • Thoroughbreds and Standardbreds most commonly affected
  • Excitable, highly strung increases risk, with fillies more prone
  • A stress-related disorder involving a disruption of normal muscle calcium regulation


  • Reduce the starch content of the diet
  • Ensure that any cereals in the diet have been cooked
  • Ensure the diet is balanced

How to achieve this:

Step 1 – Choose a mix or cube with as low a starch content as possible

Feeds which contain high levels of digestible fibre and oil, as energy sources, will be lower in starch than those which are primarily cereal-based. Ease & Excel  and Ease & Excel Cubes have been specially developed as low starch performance feeds and contain just a quarter of the starch of a competition mix yet still supply performance levels of protein, calories and other nutrients. All-Round Endurance Mix and Slow Release Condition & Competition Mix are reduced starch competition mixes and represent a significant step down in starch content from competition or racing mixes. As a general rule, cubes will also have a lower starch content than a mix with an equivalent Digestible Energy content.

Step 2 – Check that the feed used is appropriate for the type and level of work the horse is doing and fed at recommended levels to ensure a fully balanced diet

Feeds are formulated to be fed at certain levels and using the wrong one can mean that the horse isn’t receiving sufficient nutrients. Keep Calm, for example, is low in starch and suitable for horses in up to moderate work, while Ease & Excel and Ease & Exel Cubes are suitable for horses working to the highest levels. If increasing the feed results in over-exuberant behaviour or weight gain, then add a balancer to provide nutrients without energy.

Step 3 – Add an electrolyte supplement

ERS is most common in horses in hard, fast work and so an electrolyte supplement is vital to replace salts lost in sweat. Aqua-Aide can be used routinely or around an intense work period.

Management Tips

  • Warm up and cool down the horse thoroughly
  • Do not confine the horse to the stable for long periods
  • An episode of ERS often seems to occur after the horse has suffered with a virus. If you suspect your horse has a virus then reduce the workload, particularly if the horse has had RER/ERS before.


Electrolytes are minerals that, when in solution, dissociate and have electrical charges. The concentrations of electrolytes affect the movement of body fluids between cells. Most of the sodium and chloride, and much of the water, lost in sweat comes from the extracellular fluid which consists of the plasma portion of blood and the interstitial fluid which surrounds the cells in the body. Most of the potassium and some of the water comes from the intracellular fluid (water inside the cells).

The most effective way to re-hydrate a horse is to supply water and electrolytes as this is more effective than either on their own. Ideally, electrolytes should therefore be added to the water or if this puts the horse off drinking, add them to the feed but make it wet and slushy.

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