EPSM University of Minnesota report-genetics
I wanted to share this report since it has a lot of valuable information. I hope it copy and pastes ok. I have to post this report in parts, since it is too long to post as a whole:
University of Minnesota
Veterinary Diagnostic Laboratory
Age: 1995 Sex: Female
Specimen: Hair from Belle.
Diagnostic report: Your horse was tested for type 1 PSSM characterized by a mutation in the GYS1 gene.
The genetic test result for the submitted sample is as follows:Type 1 PSSM (GYS1 ): P/N
Interpretation of genetic test
Your horse has tested positive for Type 1 PSSM. Each horse has two copies of every gene (known as its genotype), one inherited from the dam and one from the sire. Every horse inherits either a normal form of the GYS1 gene or a mutant gene of the GYS1 gene form each parent. We have designated the letter P to indicate the mutant PSSM GYS1 gene and N to indicate the normal GYS1 gene. A normal horse is designated as N/N. A horse with Type 1 PSSM may be heterozygous P/N or rarely homozygous P/P for the mutation. Those horses that are P/P are often more severely affected and harder to manage.
Other acronyms have been used to describe polysaccharide storage myopathy including EPSM and EPSSM. Our laboratory has consistently used the term PSSM. Our research (January 2008) also indicates that there are two forms of PSSM (Type 1 and Type 2) in horses. Type 1 PSSM is due to a specific genetic mutation in the
GYS1 gene affecting glycogen synthesis. It occurs in over 20 different breeds to date including Quarter Horses, American Paint Horses and Appaloosas as well as Draft, Draft crossbreeds, Hafflingers, some Warmblood breeds, Morgans, Tennessee Walkers and other breeds. At present no Standardbreds, Arabs or Thoroughbred have been diagnosed with Type 1 PSSM, although sample numbers are limited. Horses with Type 2 PSSM do not possess the GYS1 genetic mutation present in Type 1 PSSM. Type 2 PSSM can only be diagnosed in horses by muscle biopsy where glycogen and abnormal polysaccharide has a characteristic appearance. We are currently working to
identify the basis for Type 2 PSSM and to determine which breeds are affected. Thus, although the type 1 PSSM (GYS1 mutation) is the most common genetic cause of PSSM and tying up in Draft and Quarter Horse related breeds there are other causes of tying-up. If horses affected with chronic muscle diseases are negative for Type 1 PSSM we recommend follow up with a muscle biopsy to investigate other possible causes. See http://www.cvm.umn.edu/umec/lab/home.html, for information on obtaining and submitting a muscle biopsy to the Neuromuscular Diagnostic Laboratory.
The type 1 PSSM mutation we have discovered is inherited in a dominant fashion, meaning that one copy of the mutation is sufficient to cause PSSM. This is different from diseases such as HERDA and GBED, which are inherited in a recessive fashion, and 2 copies of the mutant gene are required for disease. Because type 1 PSSM is inherited in a dominant fashion the chances of an affected foal being born are dependant on the genotype of the parents as follows;
(Go to University of Minnesota's website to view chart)
For example, breeding a P/N horse to an N/N horse gives a 50% chance that the offspring will have type 1 PSSM. Thus any time a horse with type 1 PSSM is bred there is a minimum chance of 50% of an affected foal being born even if the selected mate is completely normal. The risk of producing an affected offspringwhen breeding a horse with PSSM is much higher because it is a dominant disease. Unlike the recessive diseases, where a horse with one copy of the gene is a ˇ§carrierˇ¨ a horse with one copy of the type 1 PSSM mutation has PSSM.
Genetic modifiers of PSSM
Some horses with particularly severe or recurrent forms of PSSM possess a second mutation in another gene, known as the RYR1 gene that is responsible for MH (also known as malignant hyperthermia). We recommend testing for this mutation if this describes your horse (see website for testing http://www.vdl.umn.edu/vdl/ourservic...omuscular.html) The MH mutation is rare in the Quarter Horse population but when it occurs together with the type 1 PSSM mutation it makes signs of tying up more severe. In addition, in some horses this mutation results in a higher risk of developing severe anesthetic reactions such as very high body temperature, lactic acidosis, muscle damage and death under general anesthesia.
What Causes PSSM?
Horses with polysaccharide storage myopathy (PSSM) accumulate excessive amounts of the normal form of sugar (glycogen) in their muscles as well as an abnormal form of sugar (polysaccharide). Clinical signs of PSSM are usually those of tying-up, where horses develop muscle stiffness, soreness and reluctance to work with exercise. However, signs found in Draft, Draft crossbreeds, include muscle atrophy, weakness and gait abnormalities. Some horses with PSSM that are managed well show no clinical signs. Type 1 PSSM is caused by an inherited defect in the GYS1 gene (called glycogen synthase) that results in abnormal regulation of glycogen metabolism in skeletal muscle. This appears to disrupt energy metabolism. We do not know yet what the defect is that causes Type 2 PSSM.
Management of PSSMSigns of muscle pain, atrophy and stiffness in horses with both types of PSSM can be managed through specific diet and training regimes. Both diet and training must be changed to see a beneficial effect. The diet is altered to minimize starch and sugar content. This means eliminating sweet feed, corn, wheat, oats, barley, and molasses. Alternative calories are supplied in the form of fat. An equally important part of PSSM horse management is daily exercise. Consistent exercise enhances glycogen utilization, increases enzymes needed to burn fat and improves energy metabolism in skeletal muscle. To burn fat efficiently, horses need a gradual training program in addition to more fat in their diet. Approximately 90% of horses experienced fewer or no episodes of tying-up if the recommendations provided below are
followed. At present, the best we can do is to use management techniques in order to reduce recurrence. Many horses with this muscle disorder have recurrent episodes of tying-up
Provide daily turnout and avoid Rest:
For chronic cases, prolonged rest after an episode appears to be counterproductive and predisposes PSSM horses to further episodes of muscle pain. With PSSM it is NOT advisable to only resume exercise when serum CK activity is normal. Rather, horses should begin small paddock turn out as soon as reluctance to move has abated. Providing daily turn out with compatible companions can be very beneficial as it enhances energy metabolism in PSSM horses. Grazing muzzles may be of benefit to PSSM horses turned out on pastures for periods when grass is particularly lush. Most PSSM horses are calm and not easily stressed, however, if stress is a precipitating fact, stressful environmental elements should be minimized.
Re-introduction of exercise after an acute episode of ER in PSSM horses needs to be gradual. Important principles include 1) providing adequate time for adaptation to a new diet before commencing exercise (2 weeks), 2) recognizing that the duration of exercise is more important to restrict than the intensity of exercise (no more than 5 min walk/trot to start) 3) ensuring that exercise is
gradually introduced and consistently performed and 4) minimizing any days without some form of exercise. Exercise should begin with light slow uncollected work on a longe-line or under saddle beginning with once a day for 3-5 minutes at a walk and trot. This initial work should be very mild and very short in duration. Work at a walk and trot can be gradually increased by two minutes each day. When the horse can exercise for 15 minutes, a five-minute break at a walk can be provided, and then a few intervals of walk and trot can gradually be increased. At least three weeks of walk and trot should
precede work at a canter.
Regular daily exercise is extremely important for managing horses with PSSM. Even 10 min of exercise has been shown to be extremely beneficial in reducing muscle damage with exercise. Once conditioned, some PSSM horses thrive with 4 days of exercise as long as they receive daily turn out. For riding horses with type 2 PSSM, a prolonged warm-up with adequate stretching is recommended. Rest periods that allow horses to relax and stretch their muscles between 2 ˇV 5 min periods of collection under saddle may be of benefit. Horses should be worked in a long and low frame for at least 4 weeks initially with a very gradual reintroduction of collected work. The collected work should be performed in intervals lasting no more than 5 min with a period of stretching provided between intervals. The time of active collection can be gradually increased as the horse works more underneath himself and in balance. Try to exercise the horse on a daily basis even if only for 15 minutes on a lunge-line. Research has consistently shown that even 10-15 min a day will improve the function of muscle in PSSM horses. Once your horse is fit it may well manage with turn out rather than daily exercise from time to time. The number of days off a horse can manage is highly individual. If more than 3 or 4 days have gone buy begin with a small amount of exercise.
Dietary recommendations for PSSM
The first step in designing a diet for PSSM horses is to decide what the horseˇ¦s caloric requirements are and what the horseˇ¦s ideal body weight is or should be. Many horses with PSSM are easy keepers and may be overweight at the time of diagnosis. Adding excessive calories in the form of fat to an obese horse may produce metabolic syndrome and is contraindicated. If necessary, caloric intake should be reduced by using a grazing muzzle during turn-out, feeding hay with a low nonstructural carbohydrate content (NSC) at 1 to 1.5% of body weight, providing a low calorie ration balancer and gradually introducing daily exercise. Rather than provide dietary fat to an overweight horse, fasting for 6 h prior to exercise can be used to elevate plasma free fatty acids prior to exercise and alleviate any restrictions in energy metabolism in muscle.
Selection of forage:
The degree to which the NSC content of hay should be restricted below 12% NSC depends upon the caloric requirements of the horse. Feeding a low NSC hay of 4% provides room to add an adequate amount of fat to the diet of easy keepers without exceeding the daily caloric requirement and inducing excessive weight gain. For example, a 500-kg horse on a routine of light exercise generally requires 18 MCal/day of digestible energy (DE). Fed at 2% of body weight, a 12% NSC mixed grass hay almost meets their daily caloric requirement by providing 17.4 MCal/day. Thus with a 12%NSC hay there is only room for 0.6 MCal of fat per day (72 ml of vegetable oil) in order to achieve 18 MCal of energy. In contrast, a 4% NSC Blue Grama hay would provide 13.5 MCal/day which would allow a reasonable addition of 4.5 MCal of fat per day (538 ml of vegetable oil).
Selection of fat source:
The major sources of dietary fat for horses are vegetable based including vegetable oils and rice bran or animal based fat (tallow, lard, fish oil). Vegetable oils are highly unsaturated, very digestible (90-100%) and very energy dense. Suitable forms include soybean, corn, safflower, canola, flaxseed, linseed, peanut and coconut. The amount of oil added to the diet varies for each horse and should be provided in amounts that produce excessive weight gain or a cresty neck.
Starting with 1/2 cup of oil and gradually increasing the amount each week to a maximum of 2 cups is often the maximum amount needed.
Limited research has been performed on the form of oil to feed PSSM horses. Long chain fats fed in the form of corn oil or a ricebran/soy oil supplemented feed had a beneficial effect on lowering serum CK activity. Whether there is any direct beneficial effect on skeletal muscle of providing energy in the form of Omega 3 versus Omega 6 fatty acids has yet to be determined. Corn oil, sunflower oil, and safflower oil
are high in Omega-6, and lower in Omega-3, whereas soybean and canola oils are moderately high in Omega-6 and Omega 3 and flax seed, linseed and fish oils contain more Omega-3 than Omega-6. It is usually cost-prohibitive to provide sufficient energy to a PSSM horse each day in the form of Omega 3 fats. Soybean and canola oils provide a relatively affordable alternative with moderately high Omega 6. Due to the potential additional oxidant stress of fats, vitamin E (1000 ˇV 6000 U/day) should be fed to horses receiving high oil diets.
Low starch high fat concentrates:
While oils are energy dense and inexpensive, they have the disadvantages of being messy, unpalatable to some horses, prone to rancidity in warm temperatures, and difficult to feed in large amounts. As such a number of concentrates have been developed that contain fats. The important principle to be met by such feeds is that the starch and sugar components are low
enough and fat supplementation high enough to ensure that in the total diet, the calories supplied by NSC comprise no more than 10-15% of the daily DE and the calories supplied by fat comprise about 12-15% of daily DE. Common fat sources used in such concentrates include, in addition to the oils mentioned above, stabilized rice bran or animal fats. Rice bran and its products are palatable to most horses, have a
moderate NSC content ~25% by weight, contain ~20% fat by weight as well as vitamin E and are naturally high in phosphorus. The NSC component of rice bran can vary if the manufacturing process is not careful to exclude the white rice grain. Commercial rice bran products occur as powder or an extruded pellet, and are considerably more stable in warm temperatures compared to animal fat and vegetable oils.
The effect of low starch, high fat diets on exercise-induced muscle damage has only been demonstrated under controlled conditions in Quarter Horses. There is a great deal of variation in individual tolerance of PSSM horses to dietary starch; horses with more severe clinical signs of PSSM appear to require the greatest restriction in starch intake. A number of well balanced low starch high fat commercial diets are
suitable for horses with PSSM. Some commercial feeds meet the recommended nutritional needs of PSSM horses in one pelleted ration, These feeds typically contain at least 10-15% fat by weight and less than 20% NSC by weight. Some feed companies offer similar nutritional content by blending two or more manufactured feeds or by supplementing with oils or rice bran. At present, the NSC content of equine
feed products is not consistently listed on the feed tag, and consultation with the feed manufacturer is necessary to obtain this information. Nutritional support is available through most feed manufacturers in designing an appropriate diet.
The beneficial effect of the low starch, high fat diet is believed to be the result of less glucose uptake into muscle cells and provision of more plasma free fatty acids for use in muscle fibers during aerobic exercise. Quarter Horses naturally have very little lipid stored within muscle fibers and provision of free fatty acids may overcome the disruption in energy metabolism that appears to occur in PSSM Quarter Horses during aerobic exercise. This beneficial effect requires that horses are trained daily to enhance enzymes involved in fat and glucose metabolism. Exercise recommendations are provided in the proceedings from this meeting under PSSM.
It is important to note that a horse diagnosed with PSSM will always have an underlying predilection for muscle soreness and the best that can be done is to manage horses to minimize clinical signs. With adherence to both the diet and exercise recommendations about 70% of Warmblood horses show notable improvement in clinical signs and many return to acceptable levels of performance. There is, however, a wide range in the severity of clinical signs shown by horses with PSSM; those horses with severe or recurrent clinical signs will require more stringent adherence to diet and exercise recommendations in order to regain muscle function.
Re-Leve®** by Hallway Feeds (www.Re-leve.com) In Minnesota, Re-Leve is carried by Assurance Feeds\Phone (651) 463-8041.Developed with University of Minnesota researchers,
Re-Leve is the only feed proven to be effective for PSSM and is good for finicky eaters. Starch content is low (9.0% by weight) and fat content high (12.5% by weight). Additional selenium should not be fed.
Two forms of Re-Leve exist.
Re-Leve original is for hard keepers needing more concentrate to maintain body weight.Feed 8-10 lbs for thin horses or horses in heavy work
Re-Leve Concentrate is best for many PSSM horses that are easy keepers3-5 lbs fed for light to moderate work
For overweight horses, work with your veterinarian and avoid excessive fat supplementation.
One approach would be to reduce hay to 1% of body weight and feed 1-3 lbs of
For growing horses:
Weanlings: 6.5 lbs Re-Leve® and a mixed grass/alfalfa hay (8lbs per day)
Yearlings: 8 lbs of Re-Leve® and a 50-50 alfalfa/grass hay (9 lbs per day).
(**a portion of the proceeds from the sale of Re-Leve® are directed to Dr. Valberg)
by Purina in the USA: www.purinamills.com. Or Phone 800-227-89416-8lbs per day
Safe Choice®by Nuterna. www.nutrenaworld.com.
6 lbs per day combined with Empower® at 2 lbs/day
UnTiavailable in Canada is a low starch and high fat feed
There are now several other low starch and high fat feeds available. Please speak to a nutritionist regarding these feeds. The quality of ingredients may vary so make sure you are working with a reputable company. At a minimum they should meet the nutritional requirements provided in Table 1.
In general, the starch content of the feed should not be greater than 15-20% by weight and the fat should be greater than 10% by weight.
Blending of individual feeds
Fat supplements combined with additional protein/ vitamin/mineral mixes and a fiber base can be custom blended. You may find in the end that this is not a cost saver. Consult with the manufacturer’s nutritionists to formulate the correct blend for a PSSM horse which is specific to breed and level of use using the values in
Stabilized rice bran
EquiJewel® Kentucky Equine Research, Phone 859 873 1988, Fax 859 873 3781, Email
Natural Glo® (rice bran) Alliance Nutrition. Phone 1-800 680-8254 email
, website www.admani.com/Alliance Equine/
Ultimate Finish® by Buckeye Nutrition, PO Box 505, 330 E. Schultz Ave. Dalton, OH 44618.
Phone: 1-800-898-9467 Fax: (330) 828-2309,
Soy oil or Corn oil gradually can be added at 1-2 cups per day to a fiber base such
as hay cubes or alfalfa pellets. Add 600 U of vitamin E/cup of oil per day.
Prognosis for PSSM
The best indicator as to whether horses with PSSM will be productive athletes is their past performance combined with response to changes in exercise regimes and diet. Genotype or biopsy findings cannot predict future athletic potential. Horses with PSSM will always have a predisposition to muscle soreness and will require longterm management of their condition. Type 1 PSSM is inherited as a dominant trait meaning that 50% of offspring will inherit the condition no matter to whom the affected horse is bred.
Conflict of Interest Statement:Drs. Valberg, Mickelson and McCue own the license for PSSM testing and receive sales income from its use. Their financial and business interests have been reviewed and managed by the University in accordance with its conflict of interest policies. Dr. Valberg receives a portion of the profits of the sale of Re-Leve. Table 1. Nutritional requirements for an average sized horse (500 kg /1100 lbs) with PSSM at varying levels of exertion. Note NSC refers to the soluble sugar + starch. Fructans in forage are not considered in this calculation as they are not considered likely to impact the glycemic index.
Maintenance Light Exercise Moderate
16.4 20.5 24.6 32.8
% DE as NSC
<20% <20% <20% <20%
% DE as fat
15% 15% 15%-20% 20-25%
1.5- 2 % 1.5- 2 % 1.5- 2 % 1.5- 2 %
697 767 836 906
30 33 36 39
20 22 24 26
22.5 33.5 33.8 41.3
33.8 50.3 50.6 62
52.5 78.3 78.8 96.4
1.88 2.2 2.81 3.13
Vitamin E (IU/day)
375 700 900 1000
***** Disclosure of financial interest: Drs. McCue, Mickelson and Valberg are the patent owners for the genetic testing for
GYS1 . A portion of the proceeds from this test will go towards their continued research as well as patent royalties.
This diagnostic report has been authorized by
James E. Collins, DVM, PhD, Diplomate, ACVP, Professor
--- Report ---
Fax Ph (619)9229275
Fax: Prelim: Final:
Great info, but differs from Dr.V's recommendations ...re fat content at least.
I saw somewhere to lower the amount of hay for an overweight horse to be able to use the fat. Makes sense. All about counting calories.....luckily some calories are stated in the article;-)
:?I have one of those too...
replacing some of the hay with good straw? 10 to 15%? And to be extra mean, mix the straw in with the hay....;-)
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