Equine polysaccharide storage myopathy (PSSM or EPSM) is a genetic condition in horses that affects how muscle cells partition, generate, and store energy. This can lead to exercise intolerance, stiffness, and an abnormal gait in your horse. After diagnosis, owners often notice signs, such as tail swishing, high resting muscle tone, behavioural changes, and slight performance reductions indicating mild tying-up.

Horses with PSSM are at higher risk of tying-up, also known as exertional rhabdomyolysis. These episodes cause significant pain and are characterized by stiff, firm muscles along with profuse sweating and reluctance to move. In severe cases, the breakdown of muscle tissue can affect kidney function and can be fatal.

PSSM is most common in Quarter Horses and large draft breeds. It is estimated that up to 10% of Quarter Horses and 36% of draft horses have PSSM. [1]

Horses with this condition fall into two categories: PSSM1 and PSSM2. PSSM1 horses have a specific genetic mutation in the gene for glycogen synthase 1. PSSM2 horses show the clinical features of PSSM without this specific genetic mutation. [2]

The best way to manage PSSM horses is to provide a forage-first low-sugar and starch diet with careful attention to salt, mineral and vitamin needs. Additional calories can be supplied by dietary fat, or high-energy soluble fibre sources like beet pulp and linseed cake meal.

A consistent exercise routine can also help promote better energy generation in the muscle. Acetyl-L-carnitine supplementation also promotes efficient energy generation.

Wondering how to best feed your PSSM horse? Our equine nutritionists can look at your horse’s diet and help you come up with an appropriate feeding plan for free.

Equine Polysaccharide Storage Myopathy

PSSM is a muscle disorder characterized by abnormal accumulation of glycogen (the storage form of glucose/sugar) in skeletal muscle cells.

Horses with PSSM have more glycogen or glycogen in abnormal locations in their muscles. Some also form abnormal polysaccharide molecules that are not available as a fuel for the muscle cells.

Types of PSSM

There are two main types of PSSM: PSSM1 and PSSM2. [4] PSSM1 is known to be caused by a mutation in the glycogen synthase 1 (GYS1) gene. [2]

PSSM2 refers to horses with abnormal glycogen storage that do not have a mutation in the GYS1 gene. In most of these horses, the underlying cause has not yet been identified.

PSSM1

PSSM1 was first identified in 1992 in Quarter Horses that were affected by recurrent exertional rhabdomyolysis. Researchers analyzed muscle samples from these horses and found higher amounts of glycogen than normal and an abnormal polysaccharide composed of ubiquitin and polyglucosan. [14]

Further research identified the GYS1 mutation in Quarter Horses, related breeds (Paints, Appaloosas) and some draft breeds.

In all horses, the glycogen synthase 1 enzyme is important for making glycogen in muscle cells. In horses with the GYS1 mutation, this enzyme is more active than normal resulting in more glycogen being made. [2]

Diagnosis of PSSM1

An exercise tolerance test is the first step to determine whether your horse has a muscle issue. However, this test will not provide a definitive answer as to whether they have PSSM1.

Your veterinarian will take a blood sample 4 – 6 hours after a light exercise session of no more than 15 minutes. Levels of muscle enzymes, such as creatinine kinase (CK), are typically higher after exercise in PSSM horses than normal horses.

The exercise tolerance test will indicate whether the horse’s tying-up episode can be explained by an issue in their muscles. If the test does not show elevated levels of muscle enzymes, the tying-up episode was likely due to their diet or exercise management at the time and not an underlying genetic condition.

Genetic Tests

Genetic tests are a non-invasive way to definitively diagnose PSSM1. These are available to specifically detect the R309H-GYS1 variant that causes PSSM1.

A blood or hair root sample can be taken to isolate DNA and analyze the sequence of the GYS1 gene. There are two copies of this gene (one from the mother and one from the father).

PSSM1 is an autosomal dominant condition, meaning a horse with just one copy of the variant gene from either the mother or father can show signs of the disorder. In addition, foals that have one parent with PSSM have a 50% chance of carrying the variant and developing PSSM.

The genetic test will give one of three results:

  • PSSM1 n/n: two normal copies of the GYS1 gene (negative for PSSM1)
  • PSSM1 n/P1: one normal copy of the GYS1 gene and one variant copy (positive for PSSM1)
  • PSSM1 P1/P1: two variant copies of the GYS1 gene (positive for PSSM1)

A PSSM1 diagnosis can also be based on evaluation of muscle biopsies in which the veterinarian takes a sample of one of the large muscle groups and sends it to a lab to be analyzed for: [5][9]

  • Presence of amylase-resistant, periodic acid-Schiff (PAS)-positive, abnormal polysaccharide inclusions
  • Glycogen levels that are 1.5 – 2 times higher than normal
  • Higher amount of damaged or necrotic (dead) muscle fibers
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PSSM2

PSSM2 horses show the same clinical signs as PSSM1 horses, including muscle stiffness, pain, and reluctance to work. Muscle biopsies taken from these horses also show abnormal accumulation and/or location of glycogen.

However, these horses do not have the GYS1 mutation and the precise genetic cause is currently unknown. It is possible that several abnormal genes can contribute to this trait.

PSSM2 is more commonly found in warmblood and Arabian horses.

Some of those horses actually have myofibrillar myopathy (MFM). [11][12]

In MFM, there is structural damage to the muscle fibers caused at least in part by severely decreased antioxidant activity. [13] This damage allows glycogen to pool between damaged fibers leading to the PSSM2 diagnosis. To distinguish from PSSM, MFM can be properly diagnosed by staining for accumulations of the muscle protein desmin.[11][12]

Diagnosis of PSSM2

There are commercially available genetic tests that claim to identify PSSM2 genetic variants, however, research showed no difference in frequency of those variants in horses with or without PSSM2.

Healthy control horses were just as likely to have the P2, P3 or P4 variants as horses with PSSM2 or myofibrillar myopathy (MFM), another muscle disorder.

This means that the currently available genetic tests for PSSM2 are inaccurate. Note that there are no regulatory requirements for commercial genetic tests in horses. [6]

Instead of relying on genetic tests, horses should be diagnosed with PSSM2 if they show the features of PSSM1 without the GYS1 mutation. If your veterinarian suspects PSSM and has ruled out PSSM1, this is often when a muscle biopsy is recommended.

Diagnosis is typically based on chronic tying-up with or without elevated muscle enzyme levels and abnormal findings in muscle biopsies. During non-genetic disorder tying-up, muscle enzymes are still elevated but not typically during a short exercise tolerance test.

Signs of PSSM

Your veterinarian might suspect PSSM if your horse is showing one or more of the following signs: [3]

  • Chronic exertional rhabdomyolysis (tying-up)
  • Poor performance and lack of energy
  • Muscle wasting and weakness
  • Gait abnormalities
  • May show signs of back pain or whole body pain
  • Behavioural issues when saddled, reluctance to stand for the farrier

These symptoms can range from mild muscle cramping and stretching out to severe muscle pain with tissue breakdown. In the most severe cases, the horse is unable to rise to stand. In draft horses, the primary sign can be profound weakness.

The stretched-out stance and obvious pain may be misinterpreted as indicating colic or laminitis.

Clinical Signs in PSSM Horses

If your horse has already been diagnosed with PSSM and shows any clinical signs (mild to severe), contact your veterinarian. Blood samples can be run to determine if your horse is experiencing a clinical case.

Addressing PSSM when symptoms are mild reduces the risk of severe problems (including kidney damage and muscle necrosis) and improves recovery time.

Collecting blood samples when the horse has been symptom-free for a longer period (1-2 months) will help your veterinarian determine your horse’s baseline for muscle enzyme levels. Enzymes are often slightly elevated compared to non-PSSM horses.

Nutritional and Exercise Management

There is currently no cure for PSSM1 or PSSM2. However, adopting an appropriate nutrition and exercise program can reduce the incidence of severe symptoms, such as severe tying-up.

Feeding and exercise guidelines have primarily been researched in horses with PSSM1. However, a recent study in warmbloods with PSSM2 showed that the same strategies outlined below are effective for PSSM2. [4]

The following is a list of nine important tips for managing horses with PSSM.

1) Provide a low starch and sugar diet

It is important to minimize sugar and starch in your horse’s diet to help prevent excessive accumulation of glycogen in muscle tissue.

Sugars in the diet trigger insulin release from the pancreas, which stimulates glucose uptake into muscle and glycogen synthesis.

Horses with PSSM are highly insulin sensitive and have greater glucose uptake into muscle than other horses. [7]

Providing a diet that is low in starch and sugar will help limit the release of insulin and the stimulation of glycogen synthesis. However, muscle can also take up glucose by pathways which do not require insulin. The enhanced activity of the GYS1 gene makes their muscle continuously “hungry” for glucose.

It is recommended that the total diet provide less than 10% of the energy from hydrolyzable carbohydrates (HC). The HC value is calculated from the combination of ethanol-soluble carbohydrates (ESC) and starch.

These are the carbohydrate components which are digested and absorbed in the small intestine and contribute directly to increased insulin. HC differs from non-structural carbohydrates (NSC) which describes carbohydrates found within plant cells and includes compounds such as fructans which do not stimulate insulin secretion.

Low HC Diet

There are a few things to consider for lowering the HC content of the total diet:

  • Eliminate concentrate feeds: These often contain processed grains that are high in starch and sugars. Many complete feeds and commercial rations are high in HC, and not all disclose the starch and sugar content on the label. Consult a nutritionist to select appropriate feeds for your horse.
  • Choose a low-HC hay: If possible, select a hay with a HC value of 12% or less.
  • Soak high-HC hay: Soaking hay helps reduce the level of sugars. Aim for 30 minutes (with warm water) or 60 minutes (with cold water) and allow it to drain for 10 minutes afterwards.
  • Use a slow feeder hay net: This helps extend the foraging time so that any HC they are consuming enters the body over a longer period of time and results in lower insulin release.
  • Use a grazing muzzle: If fresh, lush pasture cannot be avoided, consider using a grazing muzzle to limit or completely prevent their intake.
  • Limit pasture access to the early morning: Another option for lowering sugar intake from pasture is to limit pasture access to the early morning hours when the plants naturally have lower sugar levels. However, this will not be the case if nighttime temperatures were under 40 – 45oF (4.5 – 7oC)

Note that you should never try to lower the HC content of your horse’s diet by underfeeding forages. Not providing adequate forage can lead to other issues such as gastric ulcers, behavioural problems and hindgut dysfunction.

For horses that are not in work, always aim to feed 1.5 – 2% of your horse’s ideal body weight as forage. This is equivalent to 15 – 20 lbs (7 – 9 kg) of hay per day for a 500 kg (1100 lb) horse. For horses in regular work, the often need 2.5 – 3% of their body weight and can usually be fed free choice forage.

2) Meet additional caloric needs with fat or high calorie soluble fibre

Fat does not trigger insulin release and will not be stored as glycogen in muscle. Therefore, if your horse requires additional energy beyond what they are getting from their forage, fat is the preferred choice.

Horses with PSSM can have up to 20% of their caloric needs met by fat. The best sources are rich in both omega-3 and omega-6 essential fatty acids. Dry fats, also known as prilled fats, are high in trans fatty acids and should be avoided.

If the horse requires additional calories, a common recommendation is to add 1 lb (0.5 kg) of dietary fat for a 500 kg (1100 lb) horse. This can be accomplished by adding 2 cups of oil to their feed. For a 500 kg horse in medium work, this supplies 18.6% of their required calories and is equivalent to approximately 4.5 pounds of good quality hay.

It is important to accurately assess your horse’s current body condition to determine whether they need additional calories. A body condition score of 4 or less would suggest that they could benefit from added calories.

Even if your horse does not need to gain weight, feeding added fat but at a lower rate may help improve PSSM symptoms. The usual recommendation is one cup per day.

In a small study of 4 horses, exercise tolerance improved in horses fed diets providing 12% of calories from fat instead of 7%. However, this diet had lower starch content (3% compared to 21% of calories from starch) making it difficult to determine if the benefit was from high fat or lower starch. [10]

Best Fat Sources for PSSM Horses

Some options for low-NSC fat sources include:

  • Oils: Look for omega-3 fatty acid rich oils such as fish oil, flax seed oil or w-3 oil which is high in microalgal DHA
  • Rice bran: Consists of approximately 20% fat. However, it also contains high levels of phosphorus, which needs to be appropriately balanced with calcium in the diet
  • Ground Flax: Consists of approximately 40% fat

Fat sources need to be introduced slowly to avoid digestive upset. For oils, start with 30 ml (1 oz) and increase it every 3-4 days to reach the desired amount over a 2-3 week period.

Feeding a low-NSC, high-fat diet can have additional benefits including reducing the risk of colic, laminitis and gastric ulcers.

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  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3's

Soluble fibre vs fat

A concern with high fat feeding is that it interferes with glucose metabolism. There are anecdotal reports of horses becoming cresty-necked and laminitic on high fat diets.

Several research stduies have demonstrated this effect due to providing calories from fat. For example, a single infusion of lipid (fat) solution used for intravenous feeding caused insulin resistance that lasted a week in mares. [15] Similarly, mares who had 240 mL of corn or rice bran oil added to their diet had reduced insulin sensitivity. [17] Shetland ponies fed 23.8% of their calories as fat showed a 25-fold increase in insulin. [16]

An alternative to high fat feeding is the addition of a high calorie, high soluble fiber source such as:

  • Linseed meal cake
  • Beet pulp
  • Alfalfa / lucerne
  • Wheat bran

All of these alternatives are also high protein to support muscle repair, and provide more energy/calories than grass hay.

These sources can be combined to appropriately balance the diet. For example, the high starch content of wheat bran can be mitigated by feeding it alongside the other sources. A mash with a 2:1 ratio, by dry weight, of beet pulp or alfalfa to wheat bran is suitable for PSSM horses.

Beet pulp or alfalfa can also be balanced by an equal weight of linseed meal cake or pellets.

3) Provide adequate vitamin E and selenium

Vitamin E and selenium are important antioxidants that support healthy muscle function and recovery from exercise. PSSM horses with low vitamin E and selenium intake may be more prone to muscle cramping and stiffness.

Vitamin E and selenium work together, so if the horse is deficient in one of these nutrients, the other cannot function properly.

The National Research Council’s Nutrient Requirements of Horses recommends a vitamin E intake of 500 – 1000 IU for a mature horse at maintenance.

To avoid selenium deficiency, the NRC recommends at least 1 mg selenium per day. The optimal intake is closer to 2 – 3 mg per day.

For horses prone to exertional rhabdomyolysis, it is recommended to provide 1500 – 2500 IU of vitamin E and 3 mg of selenium in the total diet. [8]

Always choose organic/chelated sources of selenium and avoid over-feeding to prevent symptoms of selenium toxicity. The upper tolerable intake of selenium for a 500 kg (1100 lb) horse is 20 mg per day.

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  • Natural Vitamin E
  • Optimal antioxidant status
  • Supports muscle function

4) Ensure adequate amino acid supply

Muscle atrophy is a common symptom of PSSM that can be partially mitigated by providing adequate levels of key amino acids in the diet.

For PSSM horses, the most appropriate strategy for providing adequate amino acid supply is to add protein or amino acid sources on their own, rather than as part of a complete feed. This helps minimize unwanted starch and sugars in the diet.

Other protein sources that provide a good balance of essential amino acids to support topline include:

The quantity of additional protein or amino acids that may be required will depend on the protein content of your hay. For horses in light to moderate exercise, the protein content of moderate-quality hay is typically sufficient to meet their needs.

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  • Topline development
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5)Supplement with Acetyl-L-Carnitine

Acetyl-L-carnitine (ALCAR) is a naturally occurring metabolite of L-carnitine which has many interesting effects on muscle metabolism and energy generation that can support the PSSM horse.

ALCAR can be split up by enzymes to produce L-carnitine and the acetyl group. The acetyl group can then bind with a molecule called coenzyme A (CoA), forming acetyl-CoA, which moves into the mitochondria and produces cellular energy. Both glucose and fatty acids must be converted to acetyl-CoA before entering the mitochondria.

L-carnitine supports the breakdown of glucose and fatty acids to produce energy. It stimulates activity of the pyruvate dehydrogenase enzyme complex to produce acetyl-CoA from glucose metabolism and feed the mitochondria [18]. L-carnitine is also required to carry fatty acids into the mitochondria to be burned.

The enzyme AMP kinase (AMPK) is also stimulated by ALCAR which directs glucose away from glycogen storage and into energy pathways. [19]

In addition, ALCAR also promotes the manufacture of mitochondria in cells to generate more of these ‘energy powerhouses’. [20]

To summarize, it supports the creation of mitochondria and both directly and indirectly provides them with fuel to improve aerobic energy generation. This enhances both the ability to perform exercise and the ability of the muscle to relax after exercise.

The recommended feeding rate is 2.2 grams per 100 kg or 1 gram per 100 pounds of body weight. This can be given twice daily for two weeks then once daily.

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6) Meet their vitamin and mineral requirements

If you eliminate complete feeds and concentrates from your horse’s feeding plan to lower the overall NSC content, you may unintentionally create a nutrient deficiency in your horse’s diet.

Horses almost never obtain all of the vitamins and minerals they require from forage alone.

In addition to selenium and vitamin E, some of the vitamins and minerals that are important for supporting metabolic health and muscle function include:

  • Zinc
  • Copper
  • Magnesium
  • B-vitamins

It is recommended to provide a low-inclusion, comprehensive vitamin and mineral supplement to ensure your horse’s needs are met without oversupplying calories. Choose a supplement that does not contain high-NSC fillers.

Mad Barn’s AminoTrace+ is a complete vitamin and mineral supplement designed with the needs of PSSM horses in mind.

AminoTrace+ provides 100% organic trace minerals, including a full profile of B-vitamins, high levels of natural vitamin E and selenium in the form of organic selenized yeast.

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7) Provide Regular Turnout

PSSM horses should be stabled as little as possible.

Movement is important to the health of all horses, but especially for horses with metabolic concerns. Pasture turnout is highly beneficial for promoting movement and encouraging utilization of glucose in energy pathways rather than for glycogen storage.

As mentioned previously, grazing muzzles are a good option for reducing grass intake and should especially be used when turnout is on lush pasture.

If stress appears to be a triggering factor for your horse, pay particular attention to their social environment during turnout to ensure they are with compatible companions.

8) Avoid long rest periods

Long periods of rest after a tying-up episode can be detrimental for horses with PSSM.

It is common to rest horses when they tie up and wait muscle enzyme levels in the blood have returned to normal. However, this is not necessary and may worsen symptoms.

Once the horse is no longer reluctant to move, they can be reintroduced to daily turnout in a calm environment. Another option is to engage in slow hand-walking to re-introduce them to exercise and avoid extended stall rest.

9) Slowly introduce training programs

If your PSSM horse has had a recent tying-up episode, ensure their return to training and exercise is gradual.

Check with your veterinarian before re-introducing work to make sure it is safe for your horse to exercise. Your veterinarian may recommend taking blood samples when the horse is asymptomatic to establish a baseline profile for the horse.

Begin with light, uncollected work on a lunge-line or under saddle, starting with just 3 – 5 minutes per day at a walk and trot. It is more important to restrict the duration of a single exercise than the intensity.

The duration of work can be increased by two minutes every day. Once they reach 15 minutes of exercise, provide a five-minute walking break after each 15-minute interval of trotting. Continue with this for at least three weeks before introducing work at a canter.

Re-introduction to collected work should also be done very gradually, beginning with just 2-5 minute periods of collection under saddle followed by an opportunity to rest and stretch.

If more than 3 – 4 days elapse without adequate exercise, start back with just a small amount of exercise.

Sample Feeding Plan for PSSM Horses

Formulating an appropriate diet for a horse with PSSM requires the following information:

  • Composition of their forage, including hay and pasture
  • Current body condition
  • Exercise level and physiological status

It is strongly recommended to get a hay analysis and work with a nutritionist to design an appropriate feeding plan.

Below are two examples of possible diets for a 500 kg (1100lb) mature horse in light exercise to support either weight maintenance or weight gain.

Feed Maintenance Diet Weight Gain Diet
(Amount / Day) (Amount / Day)
Hay 11 kg 10 kg
Ground Flax 0 0.5 kg
Canola Oil* 0 300 ml
AminoTrace+ 200 grams 200 grams
w-3 oil 100 ml 100 ml
Acetyl-L-carnitine 10 grams 10 grams
Diet Analysis
Digestible Energy (% Req) 102% 114%
HC (% Diet) 8.7% 8.2%
Fat (% Diet) 3.75% 8.45%

 

*An alternative to canola oil could be providing calories from 1 kg combined of alfalfa and wheat bran in a 2:1 mixture.

For assistance in formulating a diet appropriate for your horse with PSSM, contact our team of equine nutritionists to receive customized recommendations.

Summary

PSSM1 is a relatively common genetic condition that predominantly affects Quarter Horses and draft breeds. It leads to excessive and abnormal glycogen accumulation in muscle and altered energy metabolism. It can result in stiffness, muscle pain and increased risk of tying-up (exertional rhabdomyolysis).

PSSM2 is an inherited condition resulting in the same symptoms as PSSM1 but with an unknown genetic origin. It affects primarily warmbloods and Arabians.

Fortunately, PSSM1 and PSSM2 can be managed through diet and regular exercise. Provide a low HC diet to limit glycogen accumulation in the muscle.

Use fat or high soluble fibre foods instead of starches and sugars if additional calories are required. Gradually introduce exercise in short intervals to support glycogen breakdown and decrease the risk of tying-up.

The addition of acetyl-l-carnitine redirects glucose away from glycogen and into energy pathways while also supporting production of mitochondria for the more efficient aerobic metabolism and providing fuel for those mitochondria.

Dietary management can have a significant positive impact on the health and comfort of PSSM horses, and help to minimize the need for costly veterinary care.

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References

  1. McCue, M.E. et al. Estimated prevalence of the Type 1 Polysaccharide Storage Myopathy mutation in selected North American and European breeds. Anim Genet. 2010. View Summary
  2. McCue, M.E. et al. Glycogen synthase (GYS1) mutation causes a novel skeletal muscle glycogenosis. Genomics. 2008. View Summary
  3. Valentine, B.A. et al. Role of dietary carbohydrate and fat in horses with equine polysaccharide storage myopathy. J Am Vet Med Assoc. 2001. View Summary
  4. Williams, Z.J. et al. Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 Polysaccharide Storage Myopathy. PLoS One. 2018. View Summary
  5. Firshman, A.M. et al. Comparison of histopathologic criteria and skeletal muscle fixation techniques for the diagnosis of polysaccharide storage myopathy in horses. Vet Pathol. 2006. View Summary
  6. Valberg, S.J. et al. Commercial genetic testing for type 2 polysaccharide storage myopathy and myofibrillar myopathy does not correspond to a histopathological diagnosis. Equine Vet J. 2020. View Summary
  7. De La Corte, F.D. et al. Glucose uptake in horses with polysaccharide storage myopathy. Am J Vet Res. 1999. View Summary
  8. Harris, P.A. and Rivero, J.L.L. Nutritional considerations for equine rhabdomyolysis syndrome. Equine Vet Edu. 2015.
  9. Valberg, S.J. Muscle Conditions Affecting Sport Horses. Vet Clin North Am Equine Pract. 2018. View Summary
  10. Ribeiro, W.P. et al. The Effect of Varying Dietary Starch and Fat Content on Serum Creatine Kinase Activity and Substrate Availability in Equine Polysaccharide Storage Myopathy. J Vet Intern Med. 2004. View Summary
  11. Valberg, S.J. et al. Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis. Equine Vet J. 2016. View Summary
  12. Valberg, S.J. et al. Clinical and histopathological features of myofibrillar myopathy in Warmblood horses. Equine Vet J. 2017 . View Summary
  13. Valberg, S.J. et al. Proteome and transcriptome profiling of equine myofibrillar myopathy identifies diminished peroxiredoxin 6 and altered cysteine metabolic pathways. Physiol Genomics. 2018 . View Summary
  14. Valentine, B.A. and Cooper, B.J. Development of polyglucosan inclusions in skeletal muscle. Neuromuscul Disord. 2006. View Summary
  15. Sessions, D.R. et al. Development of a model for inducing transient insulin resistance in the mare: preliminary implications regarding the estrous cycle. J Anim Sci. 2004. View Summary
  16. Schmidt, O. et al. Effects of fat feeding and energy level on plasma metabolites and hormones in Shetland ponies. J Vet Med A Physiol Pathol Clin Med. 2001.
  17. Frank, N. et al. Effects of rice bran oil on plasma lipid concentrations, lipoprotein composition, and glucose dynamics in mares. J Anim Sci. 2005. View Summary
  18. Stephens, F.B. Does skeletal muscle carnitine availability influence fuel selection during exercise? Proc Nutr Soc. 2018.
  19. Fisher, J.S. et al. Activation of AMP kinase enhances sensitivity of muscle glucose transport to insulin. Am J Physiol Endocrinol Metab. 2002.
  20. Cassano, P. et al. Acetyl-L-carnitine feeding to unloaded rats triggers in soleus muscle the coordinated expression of genes involved in mitochondrial biogenesis. Biochim Biophys Acta. 2006.