Feeding Horses with Special Nutritional Needs

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By Shelagh Niblock, PAS

Receiving a diagnosis of the condition behind your horse’s health or performance problem is usually a relief, but the satisfaction of getting the diagnosis can be quickly replaced by fear and uncertainty regarding what to do about it. Questions around both the long-term prospects for your horse and the costs involved to support the horse with such a condition can be daunting. Owners of horses diagnosed with special nutritional needs often feel bewildered and frustrated as they attempt to put together an appropriate management protocol.

What Constitutes A Special Nutritional Need For A Horse?

Horses with special nutritional needs are those whose health is dependent on management of the nutrients which would otherwise be a regular part of the equine diet. Frequently, the management of these nutrients will ensure better performance, but sometimes reducing or eliminating a nutrient from the affected horse’s diet can be a life or death matter. Regardless of whether you care for your horse at home or board him at a top-notch facility, including or excluding certain nutrients can be a challenge.

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A veterinarian can diagnose the condition behind your horse’s health or performance concerns, and explain the horse’s long-term prospects as well as the costs of management. Photo: Clix Photography

Once you have a diagnosis of your horse’s condition, it is important to develop a plan with your veterinarian as to what management protocols will be the most effective in addressing the issue. Sometimes there are pharmaceutical options that can help the horse lead a productive life, and frequently there are diagnostic tools, like blood work and timely radiographs, that can assist the owner in managing the condition. It can be helpful to know if there is a genetic reason for the condition, if it relates to diet and exercise, or if it is a combination of the two. In any case, it is very important to get a handle on the amount of the specific nutrient(s) of concern in the diet, and to find a way to regulate it in the management of a horse with special nutritional needs.

Related: Equine Colic - Signs, Symptoms, Treatment

Start With Carbohydrate Management

Before we talk about equine diseases related to carbohydrates, it is helpful to remember that they are a big class of nutrients, including simple sugars like fructose and glucose, as well as complex sugars called fructooligosaccharides or fructans. Also included in the carbohydrate group are starches, and cellulose or fibre, which is a very complex carbohydrate. In general, simple sugars and starches are digested in the stomach and small intestine of the horse, while the complex fructans and fibre are fermented by the beneficial microbes in the hindgut of the horse. There are several metabolic conditions of horses requiring the regulation of carbohydrate intake in their diets.

Insulin Dysregulation

The metabolic conditions insulin resistance (IR), equine metabolic syndrome (EMS), and pituitary pars intermedia dysfunction (PPID), often called Equine Cushing’s disease, can all be impacted by the intake of carbohydrates that affect the insulin status of the horse. Horses with any of these metabolic conditions usually have some degree of insulin dysregulation; in other words, they have lost the ability, or possibly never had the ability, to regulate glucose and insulin in their bodies.

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Metabolic conditions, such as pituitary pars intermedia dysfunction (PPID), often called Equine Cushing’s disease, are impacted by carbohydrate intake which affects the horse’s insulin status. Photo: Clix Photography

These horses must be on a diet containing minimal simple sugars (ESC) and/or starch, as the blood glucose spikes initiated by the consumption and digestion of these nutrients will cause corresponding insulin spikes and, consequently, the potential for poor health and performance outcomes. Problems such as regional adiposity (accumulation of fat in certain areas), tying up, poor energy status (often misdiagnosed as laziness), as well as laminitis, can all be the result of the failure to regulate the intake of starch and ESC in horses with these metabolic conditions. These horses need small meals fed regularly with sugar and starch avoided as much as possible. Feeding management should include minimizing soluble carbohydrate to amounts that will not precipitate a large blood glucose increase. A summary of peer reviewed research conducted over the last 15 years on this subject (Equine Applied and Clinical Nutrition: R. Geor, P.A. Harris, M. Coen pub 2016) suggests that starch and sugar intake in excess of 1.5 grams per kg of body weight (BW) per meal will precipitate a blood glucose spike and a corresponding insulin increase. Research suggests that horses with insulin dysregulation should not consume more starch or sugar during any meal than 0.3 grams/kg of BW to avoid blood glucose and insulin spikes. Feeding forage like hay does help regulate the uptake of glucose from the equine foregut, but it is important to source a hay with non-structural carbohydrates or NSC (water-soluble carbohydrates plus starch) of less than 10 to 12 percent.

Related: The Scoop on Supplements

There have been discussions as to whether fructooligosaccharides (fructans) need to be regulated or even quantified in the diets of horses with insulin dysregulation. Because fructans are large complex molecules that resist digestion in the foregut, and therefore are unlikely to influence insulin status of the horses, some think they are of no consequence in the diets of horses with the above-noted metabolic conditions. This, however, is an area of active research, and it is still not well known how these big carbohydrate molecules behave in the equine foregut; consequently, if you have a horse with insulin dysregulation, fructans — part of the water-soluble carbohydrates (WSC) carbohydrate fraction on your lab analysis — should at least be monitored in the nutrient management plan for your horse.

Tying Up

The metabolic circumstances when horses experience painful tying up episodes are multifaceted and complicated. The term “tying up” refers to syndromes where the large muscles in the horse’s body are subject to painful contractions, causing acute pain following strenuous exercise. In the past, this condition has been called a multitude of names, including azoturia and “Monday Morning Disease,” but researchers have concluded that this set of symptoms can be caused by more than one condition, and now refer to them by the term equine rhabdomyolysis syndrome (ERS). The condition can be related to overtraining or overuse, poorly balanced diets, stress, underlying genetic abnormalities, or a combination of all of these. Disease conditions within the definition of ERS generally fall into one of two categories: chronic (when the condition is related to intrinsic or genetic characteristics in the muscle), or sporadic (when the conditions are caused by circumstances in the horse’s environment).

Horses with ERS will need a veterinary examination and diagnostic work to determine which of the two categories the syndrome falls into. Sometimes the condition is related to sporadic circumstances, such as diet imbalance, work, and/or some other stress, but the horse has no genetic abnormality in the muscle. It becomes very important for the owners of these horses to ensure that they do not overtrain them for performance, that they allow sufficient rest between performances, and that the horse’s diet is balanced and contains sufficient electrolytes and antioxidants such as selenium and vitamin E. Many of these horses do better on diets that limit sugar and starch but include additional fat.

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The painful condition of tying up is related to overtraining and overuse, poorly balanced diet, genetic abnormalities, stress, or a combination of these causes. Photo: Pam MacKenzie

Diseases such as polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (RER) are suspected to be genetic in origin and so fall into the chronic category of ERS. PSSM has now been divided into two categories: PSSM Type 1 and PSSM Type 2, both of which are genetic in origin but affect different parts of the muscle cell. Both PSSM Types 1 and 2 are typically associated with different breeds: PSSM Type 1 is more likely to be found in Quarter Horses and associated breeds, as well as Warmblood and Cob-type breeds. Conditions with similar symptoms but different genetic markers are classified as PSSM Type 2. Both PSSM and RER can be determined reasonably effectively through diagnostic work done by your veterinarian.

Diet management for PSSM/RER horses includes similar parameters as those of the horse with sporadic ERS. Therefore, balancing for trace minerals and electrolytes is important. However, because both PSSM Types 1 and 2 and RER are conditions with muscle dysfunction associated with the metabolism of glucose, affected horses MUST have diets that are low in both sugar and starch.  Hay with an NSC of less than 12 percent is advisable, and soaking hay to remove excess carbohydrate may be beneficial for some horses. Meals including good quality fibre can be beneficial, as the carbohydrate fibre or cellulose is fermented in the hindgut and does not overly influence the storage of glucose in the muscle. Feeding oil or fat sources to PSSM horses appears to offer benefits, even when very low NSC hays are fed. Oil must be fed in small, frequent meals, and shouldn’t exceed 0.5 kg per day, to be fed in not less than three meals per day.

Related: Managing the Senior Performance Horse

The feeding of additional antioxidants, such as selenium and vitamin E, can also be beneficial. Aim to feed selenium from both organic (selenium yeast) and inorganic (sodium selenite) sources. The minimum daily recommendation for selenium for a 500 kg horse is about 1 mg, and the maximum safe amount of total dietary selenium from all sources is 2 mg/kg of dry matter intake (National Research Council Nutrient Requirements of Horses, Sixth Revised Edition, 2007). That means that a 500 kg horse consuming 2 percent of his body weight in dry matter per day (10 kg of dry matter intake) could safely consume 2 mg x 10 kg dry matter = 20 mg of selenium from all sources, per day. In order to account for all possible sources of selenium in the diet and not over-supplement, a safe amount of supplemental selenium for the 500 kg ERS horse is 3 to 4 mg per day. Vitamin E is a powerful antioxidant and should be supplemented for PSSM/RER horses. The source should be organic d-alpha-tocopherol, the chemical name for natural source vitamin E, and it is reasonable to add anywhere from 2000 to 8000 IUs per day to the diet of the ERS horse. The hallmark of a successful plan for the ERS horse is a balanced exercise regimen, minimizing stress as much as possible, and a diet balanced for electrolytes but containing lower amounts of sugar and starch, extra fat, and additional antioxidants like vitamin E and selenium.

Liver Disease

Horse with chronic liver disease or hepatic insufficiency are frequently identifiable by unexplained weight loss and poor, unthrifty appearance. Liver disease in horses can be determined through a number of diagnostic tests administered by your veterinarian. Many of our typical North American equine diets are higher in protein than needed for horse health and performance. This is in part due to the energetic marketing of equine supplements, but it is also due to the fact that we have access to very high quality forages for horses. While a healthy horse can handle excess protein in their diet, a horse with compromised liver function cannot. Excess protein intake cannot be properly metabolized by a horse with liver damage, and may lead to health problems owing to the accumulation in the liver of undesirable metabolites; on the other hand, diets too low in protein may force the horse with hepatic insufficiency to mobilize amino acids from body tissues. Horses with liver damage are also very likely to be insulin resistant, which means that balancing energy intake is important.

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The horse with compromised liver function needs less protein than that provided by many commercial feeds. Look for grass hay with protein of 9 to 11 percent, and a concentrate with less than 10 percent protein. Photo: Pam MacKenzie

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Small frequent meals of added fat or oil can benefit horses with liver disease that need extra energy. Photo: Pam MacKenzie

Diets for the horse with compromised liver function need to include adequate protein, but this is frequently less protein than that contained in most commercial feeds, so aim for a concentrate that is less than 10 percent protein. Grass hay with a protein of 9 to 11 percent is a good foundation of a safe diet for the liver compromised horse.

Horses with liver disease that need extra energy can benefit from small frequent meals of added fat or oil, which can be added safely at a level of 0.1 ml per kg of body weight — some horses have easily accommodated added oil (fed in multiple small meals per day) up to as much as 0.75 ml per kg of body weight, or 375 ml of oil for a 500 kg horse. It is recommended for horses with hepatic insufficiency that the fat soluble vitamins A, D, and E should be fed in an amount up to twice as much as the National Research Council minimums - 30.0 IU/kg BW, 6.6 IU/kg BW and 1.0 IU/kg BW respectively. Doubling the minimums fed of these vitamins can ensure better health for the horse and are nowhere near toxic levels. Both iron and copper are trace minerals that are metabolized though the liver. Try to ensure that the diets for horses with hepatic insufficiency meet National Research Council minimums for copper and iron, but it is best not to exceed them.

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Hyperkalemic periodic paralysis (HYPP) is a genetic mutation found in Quarter Horses descending from the Quarter Horse stallion Impressive. This mutation affects proteins found in the ionic channels that control sodium and potassium in the muscle cells of affected horses. Horses that test positive for this condition are less able to regulate sodium and potassium, two important minerals in the electrolyte balance of the horse. Affected horses have difficulty controlling muscle function and can have severe muscle tremors. The condition can be fatal, and at the very least, it will affect the performance career of the horse concerned.

Treatments for this condition all involve reducing the amount of potassium in the extracellular fluids of the body. There are pharmaceutical options, like diuretics, which increase the elimination of potassium through excretion. There are also intravenous treatments administered by your veterinarian, containing cations (Ca++ and/or Na+), which can significantly change the electrolyte balance of the horse, thereby facilitating the movement of potassium into the cells.

shelagh niblock horse nutrition, horse's diet ppid, equine cushings disease, tying up horse, metabolic conditions horse, pssm type 1 and 2 horses

The most common treatment for horses with the genetic mutation hyperkalemic periodic paralysis (HYPP) is to reduce the intake of potassium in the diet. Concentrate supplements for these horses should contain less than one percent potassium, and hay should be under 1.5 percent, as determined by forage analysis. Photo: Pam MacKenzie

The most common method of treating the HYPP horse is to reduce the intake of potassium in the diet. Research and anecdotal evidence have shown that ensuring a dietary intake of potassium of less than 1 percent of total dry matter intake will help alleviate the symptoms of this condition. Forage is by far the biggest contributor of potassium to the equine diet; consequently, owners of HYPP horses should look for concentrate supplements containing less than 1 percent potassium to help offset the potassium levels in the forage, which will inevitably be over 1 percent and possibly as much as 3 percent potassium. Forages, like hay, should be analyzed for potassium content, and, if possible, owners should try to choose a forage that is under 1.5 percent. If suitable forage is unavailable, there are manufactured feeds available with low potassium, low NSC, and moderate protein that can be used to compliment a mostly forage ration. If you own an HYPP horse and cannot find the potassium content on the label of the bag of feed you are considering, make sure you phone the manufacturer and ask what it is. All manufacturers will have that kind of information available, even if it isn’t on the tag.

Neurological Disorders

There are a variety of neurological disorders that can afflict horses. Equine protozoal myeloencephalitis (EPM) is neurological disease caused by an infective parasitic protozoa carried by opossums. The reproductive stage of the protozoa may actually infect the central nervous system of the horse, and can cause a variety of symptoms including ataxia, unusual sweating, muscle and facial tremors, and seizure or collapse. 

Another neurological condition affecting horses is equine motor neuron disease (EMND). This disease affects slightly older horses (generally in their mid-teens) that have been deficient in vitamin E intake for at least 18 or more months. It is characterized by muscle wasting, tremors, sweating, and loss of muscle control.

Related: The Beginner's Guide to the Equine Digestive System

shelagh niblock horse nutrition, horse's diet ppid, equine cushings disease, tying up horse, metabolic conditions horse, pssm type 1 and 2 horses

The health of horses with special nutritional needs depends on proper management of specific nutrients in their diet. Feed and supplement manufacturers are happy to provide you with information on exactly what their products contain. Work with your veterinarian and an equine nutritionist to develop the best management options for your horse. Photo: Clix Photography

Equine degenerative myeloencephalopathy (EDM) is a disease affecting young horses. There appears to be a genetic component in the development of this degenerative disease, but there can also be management aspects involved. Mares who have given birth to foals with the condition may well have healthy foals subsequently if they are given a good prenatal diet with plenty of vitamin E, and foals allowed to graze on fresh pasture have a reduced incidence of the disease, even if the dam has had foals with the condition in the past.

Shivers is another chronic neuromuscular condition impacting the ability of the affected horse to move properly. Affected horses usually start to display symptoms before the age of 10 years. There can be a range of symptoms, including muscle tremors when limbs are flexed and a reluctance to move. There is no known cure for this disease.

If you suspect your horse has any one of these disease conditions, immediate intervention by your veterinarian is important. There are some promising pharmaceutical treatment options for EPM available now, but treatment options for the other equine neurological conditions are few. However, horses with any of the above-noted conditions do seem to respond favourably to supplementation with natural vitamin E sources.  Intakes of 6000 to 8000 IU daily of d-alpha-tocopherol seem to help many of these horses. Natural vitamin E can be sourced in a variety of equine supplements, but it can also easily be acquired at your local drugstore in gel caps intended for the human market. For best absorption of vitamin E in the digestive tract of the horse, it is best to feed it with a fat source like flax or oil. The most available sources of vitamin E are those that have been made water soluble, such as Elevate® W.S. from Kentucky Performance Products and Nano-E® from Kentucky Equine Research, and may be available from your veterinarian. 


Metabolic conditions that we identify with special needs horses can be multifaceted and are not always straightforward to treat. Be sure you know what condition you are dealing with, and then be sure to accurately quantify the amount of the targeted nutrient in your horse’s diet. Only when you know the sources of the nutrient can you regulate your horse’s intake of it. Develop a management plan with your veterinarian and consider consulting a qualified equine nutritionist. Making small incremental changes in the diet of your horse is always advisable, and keeping records of the changes made can be very helpful in determining what the best management options are going to be for your horse. Don’t be afraid to contact the manufacturer of your selected supplements if the information on the tag and/or website is insufficient for your management needs. Most companies do provide nutritional services to consumers of their products and are happy to help you out.

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Main Photo: Clix Photography