Ask The Vet: Vitamin E & Muscle Disorders - November 12

This is a great question because it brings up several important points. First, tying-up is not due to a vitamin E or selenium deficiency in adult animals. Very young animals can develop a nutritional myodegeneration that affects both skeletal muscle, seen clinically as tying-up, and myocardial muscle (heart) that is responsive to administration of vitamin E and selenium. Nutritional myodegeneration is rare in adult animals. Second, the amount of vitamin E provided per ml of selenium provided is very small, so giving larger volumes of medication to provide higher doses of vitamin E or giving repeated doses for the purpose of providing daily vitamin E risks the development of selenium toxicity. There are other injectable preparations that consist solely of vitamin E that would be more appropriate for multiple dosing or for providing higher doses of vitamin E. Third, absorption is key in determining which is the most effective product, however absorption by the muscle tissue itself is just as important as absorption at the level of the gastro-intestinal tract. There are multiple forms of vitamin E and only one form (natural form) is biologically active in animal tissues. That is why it is important to choose a product containing natural vitamin E. Not all vitamin E products contain natural source vitamin E, including injectable preparations. Currently the most well absorbed oral vitamin E products are those that contain not only natural source vitamin E, but are also water soluble or water dispersible products such as Nano-E and Elevate by KER (www.ker.com). The purpose of supplemental vitamin E in horses with PSSM is not curative, but to provide additional anti-oxidant support to reduce oxidative damage to muscle tissues. Therefore, daily administration of vitamin E may be beneficial to horses with PSSM and oral administration is a more reasonable way to provide it verses daily intramuscular injections.

The first step in managing horses with tying-up episodes is to obtain a proper diagnosis. A definitive diagnosis of polysaccharide storage myopathy (PSSM) is made through muscle biopsy. A genetic test is also available, but may not be the most appropriate diagnostic test in all horses. For PSSM testing, please consult with your veterinarian to determine which test is best for your horse.
Typically, a diet that is low in carbohydrates and higher in fat is recommended. A vitamin E supplement may also be beneficial. Regular exercise is recommended in horses with PSSM as it has been shown to reduce clinical signs of disease. Exercise should consist of a regular fitness program as well as daily turnout to keep the horse moving. As little as 15 minutes of exercise per day has been shown to have beneficial effects for managing horses with PSSM. As far as how much exercise is recommended will depend on whether your horse is currently having episodes of tying-up with exercise. In cases where the horse is showing signs of tying-up with exercise slow gradual increases in exercise intensity and duration is recommended. For more detailed information on dietary and exercise recommendations for horses with PSSM please visit the University of Minnesota’s College of Veterinary Medicine Neuromuscular Lab (http://www.cvm.umn.edu/umec/lab/PSSM/home.html#PSSM).

The first step in managing horses with tying-up episodes is to obtain a proper diagnosis. A definitive diagnosis of polysaccharide storage myopathy (PSSM) is made through muscle biopsy. A genetic test is also available, but may not be the most appropriate diagnostic test in all horses.
 
Typically, a diet that is low in carbohydrates and higher in fat is recommended. A vitamin E supplement may also be beneficial. Because lush pasture grasses contain a high amount of sugar (carbohydrates), horses with PSSM consuming lush pasture may be at risk for future episodes of tying-up. Therefore, limiting access to lush pasture is recommended in horses with PSSM.
 
For further information on PSSM and dietary recommendations please visit the University of Minnesota’s College of Veterinary Medicine Neuromuscular Lab (http://www.cvm.umn.edu/umec/lab/PSSM/home.html#PSSM). Please consult with your veterinarian on what type of diet is most appropriate for your horse.

This is a great question and a frustrating one, for you and your veterinarian. If your horse’s activity level is limited by chronic health issues, such as lameness from arthritis, then light riding on soft surfaces at a walk may be all that he can do. If that is the case, then daily turnout to keep him moving will be especially important. It is true that regular exercise may improve clinical signs of PSSM, which is why a routine exercise program is often recommended as an important part in management of horses with PSSM.
 
The good news is that even as few as 10 minutes of exercise per day may prove beneficial. Diet also plays a key role in management of PSSM and may be even more important for your horse since exercise options are limited. Feeding a low carbohydrate, higher fat diet is recommended for horses with PSSM. A vitamin E supplement may also be beneficial.
 
Please consult with your veterinarian to determine what type of diet is most appropriate for your horse. For further information on PSSM please visit the University of Minnesota College of Veterinary Medicine’s Neuromuscular Lab (http://www.cvm.umn.edu/umec/lab/PSSM/home.html#PSSM).

There are numerous electrolyte products on the market for horses, so I am not sure which specific product you are referring to. However, in general, maintaining electrolyte balance is an important component of the nutritional management of horses with PSSM. Horses should have access to salt or they can be fed a daily electrolyte supplement, especially when the weather is hot and humid or if the horse is sweating excessively. This can be accomplished by providing a salt block or supplementing with a commercially formulated electrolyte paste or powder. Be sure to read the label as some electrolyte products contain added sugars, such as dextrose, which could affect horses with PSSM if fed on a regular basis. Please consult with your veterinarian to see if an electrolyte supplement is appropriate for your horse. For more information on PSSM and nutritional management please visit the University of Minnesota College of Veterinary Medicine’s Neuromuscular Lab (http://www.cvm.umn.edu/umec/lab/PSSM/home.html#heal).

Luckily, horse’s muscles heal completely, with minimal scarring, following an episode of tying up. The healing process usually takes several months and in cases where muscle mass appeared to be lost following the initial episode, most horses will appear normal within 6 months if properly managed and no further episodes have occurred. With proper dietary management (high fat, low starch) and a regular exercise program most horses show improvement in clinical signs and can lead a successful athletic life. Unfortunately, the key here is management, which means that horses with PSSM are never cured of the disease and relapses in clinical signs can occur if fitness levels decrease, diet changes or the horse becomes ill.
 
If you believe your horse is currently being properly managed for PSSM through a proper diet and regular exercise program, then other causes of poor performance should be ruled out by your veterinarian such as an underlying lameness or a respiratory condition, such as inflammatory airway disease. Measurement of serum Vitamin E level may also be valuable as some horses deficient in Vitamin E can show signs of muscle wasting and weakness, which could manifest as poor performance. Horses with muscle disorders may benefit from supplemental Vitamin E. Natural source Vitamin E in a water soluble form, fed at 1000 IU/day has been recommended. Please consult with your veterinarian to determine if your horse could benefit from Vitamin E supplementation. For further information on PSSM please visit the University of Minnesota’s College of Veterinary Medicine Neuromuscular Lab (http://www.cvm.umn.edu/umec/lab/PSSM/home.html#heal).

In terms of bioavailability, the most beneficial Vit E supplement in horses is one that contains only natural sources of Vit E and is in a water soluble liquid form. Water soluble Vit E supplements currently available for horses are listed below.
 
Nano•E, Kentucky Equine Research, Versailles, KYElevate WS, Kentucky Performance Products LLC, Versailles, KYEmcelle, Stewart Products, Bedford TX

Without examining Mater it is difficult to determine what could be causing his sudden change in attitude and there may be several issues at hand given his episode of hives, colic, deficient Vit E status and abnormal neurological exam. Sometimes chronic pain can cause a horse to have a poor work ethic or poor attitude in general. Muscle weakness from a muscle disorder can also cause poor performance, which may translate into a poor work ethic and attitude.
 
Pinpointing a source of pain may be challenging, but starting with a thorough physical and lameness exam to rule out signs of musculoskeletal pain, such as lameness or back pain, ect. would be a good place to start. Repeating the neurologic exam to compare pre and post Vit E treatment might provide further insight. In some horses that are Vit E deficient, muscle wasting occurs, especially over the hindquarters, resulting in muscle weakness and poor performance. A muscle biopsy can identify a Vit E deficient muscle disorder. Lastly, with a history of colic and possible stress from competition and strenous training, ruling out gastric ulcers may also be warranted. Please consult with your veterinarian for further evaluation and appropriate diagnostic recommendations for Mater.

Excessive drowsiness secondary to recumbent sleep deprivation can occur for several reasons. Horses may be reluctant to lie down due to pain. For example, a horse may be reluctant to lie down if he experiences thoracic pain from sternal contact on the ground or abdominal pain from pressure on his abdomen when recumbent. Other causes, that are non-pain related, are insecurity in the horse’s environment (i.e. the horse does not feel comfortable lying down in the pasture or in the stall) or muscle weakness, which may make the task of lying down and/or rising difficult. In reference to your question, yes it is possible that musculoskeletal pain or a muscle disorder, such as polysaccharide storage myopathy (PSSM), could cause a horse to avoid lying down due to pain or weakness when attempting to lie down or when rising.
 
Commonly reported clinical signs of PSSM in Warmbloods include firm, painful back and hindquarter muscles, poor performance and muscle atrophy. A submaximal exercise test (I believe you are referencing this in your question) is often utilized in the diagnosis of PSSM. In this test, a baseline blood sample is drawn and then the horse is trotted for 15 minutes. A second blood sample is drawn 4-6 hours post exercise. The muscle enzyme CK is measured in both samples. A greater than 3 fold increase in CK concentration is considered abnormal. However, a normal result does not rule out PSSM. Therefore, if PSSM is still suspected further testing is recommended.
 PSSM is characterized by abnormal accumulation of glycogen and polysaccharide in muscle cells. Therefore, the most definitive test is a muscle biopsy which can easily be performed by your veterinarian. A genetic test is also available and can be performed on blood or hairs, but may not be appropriate in all cases of suspected PSSM as it only identifies Type 1. Type 2 PSSM can only be diagnosed from a muscle biopsy. If you suspect your horse has PSSM or are interested in pursuing further testing, consultation with your veterinarian is recommended. For further information on PSSM and testing recommendations please visit the University of Minnesota’s Neuromuscular Lab (http://www.cvm.umn.edu/umec/lab/PSSM/home.html).

The exact cause of Shivers is unknown, however genetic, traumatic, infectious, myopathic or neurologic factors have been suggested. At the present time, there is no cure for Shivers and few treatments have been found to be effective in controlling this disease.  Some cases have reportedly shown improvement in clinical signs following periods of rest, however once exercise resumes clinical signs often return. Dietary modification to a high-fat, low carbohydrate feed along with a regular exercise program and daily turnout may reduce the frequency of muscle spasms in some cases. Additionally, supplementation with a natural source of Vitamin E (1000 IU/day) may improve clinical signs in some horses with Shivers.

Unfortunately, the long term prognosis for athleticism, and in some cases life, for horses with Shivers is poor due to the progressive nature of the disease and lack of effective treatments. Over time, spasms may occur more frequently and worsen in severity. In severe cases, muscle wasting and weakness may also develop necessitating humane euthanasia.

If you are considering purchasing a horse with suspected Shivers, consultation with your veterinarian is recommended. He or she will most likely recommend a thorough evaluation to confirm the diagnosis by ruling out other possible causes of any gait abnormalities that are present.
For more information on Shivers and current ongoing research please visit the University of Minnesota’s Equine Neuromuscular Lab website (http://www.cvm.umn.edu/umec/shivers/home.html).