Research Separates the Innovator from the Imitator

Polysaccharide Storage Myopathy: One Important Cause of Exertional Rhabdomyolysis

27 August, 2015

Polysaccharide storage myopathy (PSSM) is a glycogen storage disorder in Quarter Horse-related breeds, warmblood and draft horses that show signs of exertional rhabdomyolysis. A diagnosis should be made by muscle biopsy and identification of abnormal periodic acid Schiff's positive polysaccharide inclusions in muscle fibers. Prevention of tying-up in susceptible horses involves eliminating grain and sweet feed from the ration and adding a fat supplement such as rice bran. In addition, one of the most important factors to prevent rhabdomyolysis in these horses appears to be pasture turn-out and daily exercise. Some laboratories have diagnosed polysaccharide storage myopathy solely on the basis of an apparent increase in muscle glycogen staining. This has unfortunately resulted in the application of the term PSSM to horses of a wide variety of breeds with a variety of symptoms.

RE•LEVE Research

13 February, 2015

Dr. Stephanie Valberg
Dr. Stephanie Valberg’s gelding Brooke suffered from RER before his symptoms were alleviated by Re-Leve.

Dr. Stephanie Valberg, a researcher at the University of Minnesota, is a world leader in exertional rhabdomyolysis investigations. In conjunction with Dr. Valberg, Kentucky Equine Research created RE•LEVE.

Dr. Stephanie Valberg is an international leader in equine exercise physiology research. In particular, she has investigated tying-up syndrome extensively over the past several years. She is presently an associate professor in the College of Veterinary Medicine at the University of Minnesota. Valberg received her D.V.M. degree from the Ontario Veterinary College in Guelph, Ontario, Canada. In addition, she received a Ph.D. from the Swedish University of Agricultural Sciences in Uppsala, Sweden. In 1998, Valberg was honored with the EquiSci International Award, an honor presented every four years to the individual whose work most significantly impacts equine exercise physiology research. She is the author or coauthor of over 50 peer-reviewed publications and 10 book chapters. She has also given over 100 national and international research presentations during her career.

University of Minnesota Equine Center, Neuromuscular Diagnostic Laboratory

For the Ambitious Reader

Feeding Fat to Manage Muscle Disorders
S. Valberg, E. McKenzie
University of Minnesota, St. Paul, MN

Muscle Disorders: Untying the Knots Through Nutrition
S. Valberg, R. Geor, J.D. Pagan
University of Minnesota, St. Paul, Minnesota, R and J Veterinary Consultants,
Guelph, Ontario, Canada,Kentucky Equine Research, Inc., Versailles, Kentucky

Summary: The effect of varying dietary starch and fat content on serum creatine kinase activity and substrate availability in equine polysaccharide storage myopathy.
W.P. Ribeiro, S. Valberg,J.D. Pagan, and B. Essen Gustavsson 2004.
College of Veterinary Medicine, University of Minnesota, St. Paul, MN
Kentucky Equine Research, Inc., Versailles, KY
Large Animal Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden

Polysaccharide Storage Myopathy: One Important Cause of Exertional Rhabdomyolysis
S. Valberg, J.R. Mickleson
World Equine Veterinary Review 1997; Volume 2, Number 4.

Fit to be tied
S. Duren and S. Valberg
Equinews 1999; 3: 15-17.

The effect of feeding a fat supplement to horses with polysaccharide storage myopathy
F. De La Corte, S. Valberg, J. MacLeay and J. Billstrom
World Equine Veterinary Review 1999; 4: 12-19.

Role of electrolyte imbalances in the pathophysiology of the equine rhabdomyolysis syndrome
P.A. Harris and D.H. Snow
Equine Exercise 3, S.G.B. Persson, A. Lindholm and L.B. Jeffcott (editors)
ICEEP Publications, 1991; 435-442

Abnormal regulation of muscle contraction in horses with recurrent exertional rhabdomyolysis
L.R. Lentz, S.J. Valberg, E.M. Balog, J.R. Mickelson and E.M. Gallant
American Journal of Veterinary Research 1999; 60: 992-999

Heritable basis for recurrent exertional rhabdomyolysis in Thoroughbred horses
J.M. MacLeay, S.J. Valberg, G.J. Geyer, S.A. Sorum and M.D. Sorum
American Journal of Veterinary Research 1999; 60: 250-256

Epidemiologic analysis of factors influencing exertional rhabdomyolysis in Thoroughbreds
J.M. MacLeay, S.A. Sorum, S.J. Valberg, W.E. Marsh and M.D. Sorum
American Journal of Veterinary Research 1999; 60: 1562-1566

Muscular causes of exercise intolerance in horses
S.J. Valberg
Veterinary Clinics of North America: Equine Practice 1996; 12: 459-517

Familial basis for exercise rhabdomyolysis in Quarter Horse-related breeds
S.J. Valberg, C. Geyer, S.A. Sorum and G.H. Cardinet III.
American Journal of Veterinary Research 1996; 57: 286-290

Polysaccharide storage myopathy associated with exertional rhabdomyolysis in horses
S.J. Valberg, J.M. MacLeay and J.R. Mickelsen
Compendium for Continuing Education of the Practicing Veterinarian 1997; 19: 1077-1086

Recurrent exertional rhabdomyolysis in Quarter Horses and Thoroughbreds: one syndrome, multiple aetiologies
S.J. Valberg, J.R. Mickelsen, E.M. Gallant, J.M. MacLeay and F. De La Corte
Equine Veterinary Journal 1999; Supplement 30: 533-538.

Nano•E® Research

18 December, 2013

Form of α-tocopherol affects vitamin E bioavailability in Thoroughbred horses

J.D. Pagan, M. Lennox, L. Perry, L. Wood, L.J. Martin, C. Whitehouse, and J. Lange

Kentucky Equine Research, Versailles, Kentucky 40383,USA





Vitamin E functions as a biological antioxidant, preventing the oxidation of unsaturated lipid materials within cellular and subcellular membranes by neutralizing production of free radicals. Supplemental vitamin E may be beneficial in horses experiencing oxidative stress such as during parturition and exercise (Hargreaves et al., 2007) and for horses at risk of certain types of neurological diseases (Mayhew et al., 1987; Blythe and Craig, 1993).

Vitamin E can be obtained from natural or synthetic sources, but the chemical structure of each is different. Natural vitamin E is composed of one isomer (d-α-tocopherol [RRR α-tocopherol]), and it is the most bioactive form in human and animal tissue. Synthetic vitamin E is a mixture of eight isomers (dl-α-tocopherol [all-rac-α-tocopherol]), of which only one is identical to the natural isomer. These eight isomers vary greatly in relative biopotency. Synthetic or natural vitamin E is typically added to equine feeds in an esterifed form (α-tocopherol acetate) to prolong shelf life.

To account for differences in biopotency, the relative strengths of different forms of vitamin E are expressed as international units (IU) in which 1 mg of synthetic acetate equals 1 IU, 1 mg of natural acetate equals 1.36 IU, and 1 mg of natural alcohol equals 1.49 IU (Anon, 2000). These conversion factors were developed using laboratory animal models, and they may not be relevant for horses and humans. In fact, studies in humans have suggested that natural-source vitamin E is twice as bioavailable as the synthetic form (Acuff et al., 1998; Burton et al., 1998), and studies in horses have suggested that the relative bioavailability of natural-source vitamin E is greater than synthetic (Pagan et al., 2005; Hargreaves et al., 2007).

The following studies were conducted to determine if synthetic and natural-source vitamin E have similar bioavailabilities when administered at equal IU doses and to determine if water-dispersible forms of vitamin E are more bioavailable than lipid-soluble forms.


Materials and Methods


Two studies were conducted to assess the relative bioavailability of different forms of vitamin E. In study 1, single oral doses of three different forms of vitamin E were evaluated in eight Thoroughbred geldings (age 10.75 ± 2.2 years) during three one-week periods. The forms of vitamin E evaluated included synthetic vitamin E (dl-α-tocopheryl acetate) (SYN)a, natural-source vitamin E acetate (d-α-tocopheryl acetate) (ACT)b, and natural-source alcohol (d-α-tocopherol) (ALC)c. On the first day of each period, the horses were administered 5000-IU doses of vitamin E top-dressed on 1 kg of unfortified sweet feed at 7:00 AM. Baseline blood serum samples were collected immediately before dosing and at 3, 6, 9, 12, and 24 hours post-dosing.


In study 2, three Thoroughbred geldings (age 5.67 ± 1.2 years) were used in a replicated 3 x 3 Latin square design trial to assess the relative bioavailability of three forms of vitamin E. There were a total of six one-week periods with each horse receiving each form of vitamin E in two separate periods. The vitamin E forms studied were synthetic vitamin E (dl-α-tocopheryl acetate) (SYN)a, a micellized d-α-tocopherol (Elevate WS)d, and a d-α-tocopherol (Nano·E)e that had been nanodispersed into liposomes. Both of these processes render normally lipid-soluble vitamin E water dispersible. At the beginning of each period the horses received a single 5000-IU dose of one of the vitamin forms top-dressed onto 1 kg of unfortified sweet feed. Baseline blood serum samples were collected immediately before dosing and at 3, 6, 9, 12, 24, 36, and 48 hours post-dosing. Throughout both studies the horses were maintained on an unfortified sweet feed plus grass hay.


Serum α-tocopherol was measured using high-performance liquid chromatographyf, and relative bioavailabilities were calculated from comparisons of magnitudes of responses measured by areas under the concentration versus time curves (AUC) and by comparisons of the peak concentrations of serum vitamin E following each dose. The AUC, baseline, peak, and maximal change from baseline data were analyzed by analysis of variance (ANOVA), and a Tukey-Kramer multiple comparison was used to examine differences between treatments.


Results and Discussion


In study 1, ACT and ALC had a significantly greater AUC than SYN (P < 0.05) (Table 1). There was no significant difference in AUC between ACT and ALC. Relative to SYN, the bioavailability of ACT and ALC equaled 197% and 252%, respectively. Time post dosing to peak vitamin E was not different between treatments and averaged 9.2 ± 1.2 (mean ± SE) hours. Although there was a trend towards higher peak levels and maximal change from baseline values for the ACT and ALC treatments compared to SYN, these differences were not significantly different (P > 0.05).


Table 1 Response in serum α-tocopherol to 5000-IU doses of synthetic, natural acetate, and natural alcohol forms of vitamin E.



natural acetateb

natural alcoholc









area under curve (24 hr AUC)

5.9 ± 1.5a

11.6 ± 2.0b

14.9 ± 3.0b

baseline vitamin E (ug/ml)

3.44 ± 1.80a

3.51 ± 0.09a

3.31 ± 0.13a

Peak vitamin E (ug/ml)

3.97 ± 0.08a

4.58 ± 0.39a

4.58 ± 0.39a

Δ vitamin E (ug/ml)

0.52 ±0 .12a

1.07 ± 0.39a

0.93 ± 0.18a

abMeans for the same item with the same letter are not different (P > 0.05)


In study 2, Elevate WS and Nano·E had a significantly greater AUC than SYN (P < 0.05)(Table 2). There was no significant difference in AUC between Elevate WS and Nano·E. Relative to SYN, the bioavailability of Elevate WS and Nano·E equaled 559% and 613%, respectively. Time post dosing to peak vitamin E was not different between

treatments and averaged 12.0 ± 1.4 (mean ± SE) hours. Nano·E had significantly higher peak and maximal change from baseline values compared to SYN (P < 0.05).


Table 2 Response in serum α-tocopherol to 5000-IU doses of a synthetic and two water-dispersible forms of vitamin E.




Elevate WSd






area under curve (48 hrs)

15.62 ± 3.22a

87.36 ± 25.3b

95.85 ± 25.7b

baseline vitamin E (ug/ml)

3.04 ± .30a

3.00 ± .39a

2.86 ± .42a

Peak vitamin E (ug/ml)

3.63 ± .36a

6.01 ± 1.26ab

6.69 ± 1.39b

Δ vitamin E (ug/ml)

.59 ± .08a

3.00 ± .89ab

3.83 ±1 .15b

abMeans for the same item with the same letter are not different (P > 0.05)


The results of these studies suggest that natural sources of vitamin E have a greater bioavailability than is accounted for in the current conversion factors of 1.36 and 1.49 used in the feed industry for natural acetate and alcohol, respectively. These differences should be taken into account when calculating the quantity of supplemental vitamin E required by horses.


Natural-source water-dispersible forms of vitamin E were 5-6 times more bioavailable than synthetic vitamin E acetate, and a 5000-IU dose more than doubled serum vitamin E levels within 12 hr. These forms of vitamin E should be beneficial when a rapid increase in vitamin E is warranted such as during periods of oxidative stress (exercise or parturition) or for horses at risk of certain types of neurological disease.




Acuff, R.V., R.G. Dunworth, L.W. Web, J.R. Lane. 1998. Transport of deuterium-labeled tocopherols during pregnancy. Am. J. Clin. Nutr. 67:459-464.


Anonymous. 2000. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academy Press,Washington, D.C.


Blythe, L.L., and A.M. Craig. 1993. Equine degenerative myeloencephalopathy. Part 1. Clinical signs and pathogenesis. Equine Compendium 14:1215.


Burton, G.W., M.G. Traber, R.V. Acuff. 1998. Human plasma and tissue α-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E. Am. J. Clin. Nutr. 67:669-684.


Hargreaves, B.J., D.S. Kronfeld, J.L. Holland, L.A. Gay, W.L. Cooper, D.J. Sklan, and P.A. Harris. 2001. Bioavailability and kinetics of natural and synthetic forms of vitamin E in Thoroughbred horses. In. Proc. Equine Sci. Soc. 17:127.


Mayhew, I.G., C.M. Brown, H.D. Stowe, A.L. Trapp, F.J. Derksen, S.F. Clement. 1987. Equine degenerative myeloencephalopathy: A vitamin E deficiency that may be familial. J. Vet. Intern. 1:45.


Pagan, J.D., E. Kane, and D. Nash. 2005. Form and source of tocopherol affects vitamin E status in Thoroughbred horses. Pferdeheilkunde 21:101-102.




aROVIMIX E-50 Adsorbate (dl-a-tocopheryl acetate), DSM Nutritional Products AG, Wurmisweg 576, CH-4303 Kaiseraugst, Switzerland


bKER Equine Ester, Kentucky Equine Research, Versailles, KY 40383, USA


cNOVATOL 5-87 (d-α-tocopherol ), Archer Daniels Midland Company, Decatur, IL 62526, USA


dElevate WS®, Kentucky Performance Products LLC, Versailles, KY 40383, USA


eNano·E, Kentucky Equine Research, Versailles, KY 40383, USA


fDCPAH Nutrition, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA


EquiShure® Research

18 December, 2013

EO•3® Research

18 December, 2013

Fish oil and corn oil supplementation affect red blood cell and serum eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations in Thoroughbred horses
J.D. Pagan, T.L. Lawrence, and M.A. Lennox
Kentucky Equine Research, Versailles, KY 40383, USA


Horses require both omega-3 and omega-6 fatty acids in their diets. The omega-3 family stems from alpha-linolenic acid (ALA), while the omega-6 family originates from linoleic acid (LA). Long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are intermediates in the formation of eicosanoids that have been shown to reduce inflammatory responses, support immune function, and enhance fertility (Curtis et a~ 2000; Hall et aI., 2004; Stelzleni et aI., 2006; Vineyard et al. 2006). This study was conducted to compare the effect of supplementation with oil high in EPA and DHA (fish oil) or low in EPA and DHA (com oil) on red blood cell (RBC) and serum EPA and DHA.

Materials and Methods

Twelve Thoroughbred geldings were supplemented for 127 d with 60 ml of either fish oil (EO·3)a or com oil. They also received a basal diet of 8 kg of timothy hay and an unfortified sweet feed, soybean meal, sodium chloride, and calcium carbonate to meet NRC requirements. The horses were exercised three times weekly on a mechanical walker and turned out into small paddocks daily for 4-6 hours with muzzles to prevent grazing and housed overnight in 12 x 12 box stalls. Blood samples were taken at d 0, 29,57,92, and 127 in EDTA collection tubes before the morning feeding, placed immediately on ice, and analyzed for EPA and DHA.

Results and Discussion

By d 29, horses receiving fish oil had an average increase in serum EPA and DHA of 3.7-fold (P < 0.05) and 17.9-fold (P < 0.01), respectively (Figure I and 2). In horses receiving com oil, serum EPA decreased 1.5-fold from baseline at d 57 (P < 0.05) and fourfold by d 92 (P < 0.05). By d 127, RBC DHA concentrations in the fish oil supplemented horses was over 1.9-fold greater (P < 0.05) than baseline (Figure 3), while there was no difference observed in RBC DHA from horses receiving com oil. In the fish oil supplemented group, RBC EPA increased 11.5-fold (P < 0.05) by d 127 (Figure 4). Com oil supplemented horses had lower than baseline RBC EPA at 57 d (P < 0.05), 92 d, and 127 d (P < 0.01).

Figure 1. Serum EPA

Figure 2. Serum DHA
Figure 3.Red Blood Cell DHA
Figure 4. Red Blood Cell EPA


This study showed that 60 ml/d of fish oil supplementation increases serum and RBC EPA and DHA in horses. Com oil supplementation resulted in a decrease in RBC EPA, which may affect RBC membrane fragility.


Curtis, C.L., C.E. Hughes, C.R Flannery, C.B. Little, J.L. Harwood, B. Caterson. 2000. N-3 fatty acids specifically modulate metabolic factors involved in articular cartilage degradation.

J. Biol. Chem 275,721-724.

Hall, J.A., R.J. Van Saun, S.J. Tornquist, J.L. Gradin, E.G. Pearson, RC. Wander. 2004. Effect of type of dietary polyunsaturated fatty acid supplement (com oil or fish oil) on immune responses in healthy horses. J. Vet. Intern. Med. 18,880-886.

Stelzleni, E.L., L.K Warren, J. Kivipelto. 2006. Effect of dietary n-3 fatty acid supplementation on plasma and milk composition and immune status of mares and foals. J. Anim Sci. SuppI. 84, 392.

Vineyard, KR, L.K Warren, KA. Skjolaas, lE. Minton, J. Kivipelto. 2006. Effects of dietary fish oil and flaxseed on plasma fatty acid composition and immune function in yearling horses. J. Anim. Sci. SuppI. 84, 393.


aEO•3™,Kentucky Equine Research, Versailles, KY 40383 USA




DuraPlex Technical Bulletin

18 December, 2013

Kentucky Equine Research Technical Bulletin

The Effect of DuraplexTM Supplementation on Bone Density in Thoroughbred horses subjected to either an increasingly strenuous exercise program or complete stall confinement


Duraplex is a proprietary mixture of nutrients which is designed to improve bone density in horses. It contains minerals and vitamins known to play a role in bone formation as well as a source of milk basic proteins (MBP). In rats, dogs and humans MBP have been shown to stimulate osteoblastic collagen production (IGF-1 up-regulation) and suppress bone destruction by osteoclast cells (cysteine-protease inhibitor). Studies conducted in Japan with exercised Thoroughbreds have reported increases in serum osteocalcin and decreases in serum ICTP with MBP. These studies, conducted by the JRA, also reported greater increases in bone density during training in supplemented horses compared to controls (Inoue et al. (2006); Inoue et al. (2007).

The purpose of this study was to determine if Duraplex supplementation would affect bone density in Thoroughbreds given paddock turnout, treadmill exercise or complete stall confinement.

Materials and methods

Twelve Thoroughbreds (eight-2 year olds and four-6 year olds) were used in a 5 month, 3 phase study. Throughout the study the horses were housed in box stalls at night. During the first 28 days of the study (Phase A) the horses were turned out daily for 4-5 hours in paddocks wearing muzzles to prevent grazing. The horses were fed a basal diet of unfortified sweet feed, soybean meal, sodium chloride, and calcium carbonate to meet NRC requirements and 8 kg of Timothy hay. During Phase B of the study the horses were exercised for 12 weeks on a treadmill and mechanical walker. During Phase C of the study the horses were confined in box stalls for 28 days without exercise.

The horses were blocked by age and randomly assigned to a control and treatment group. The treatment group (four 2 year olds and two six year olds) received the basal diet plus 120 g Duraplex per day. The grain and supplement were fed at 7 am and 4 pm. Horses received hay at 7 am, 4 pm and 10 pm. Throughout the study, the horses were weighed and condition scored and their grain intakes was adjusted to maintain a desirable body condition.

Bone density measurements

To estimate changes in bone density, dorsopalmar radiographs of the third metacarpal bone(McIII) were taken on a bi-weekly or monthly basis. An aluminum step wedge was exposed simultaneously with the McIII. This was used as a reference standard. Radiographic bonealuminum equivalencies (RBAE) were recorded at three sites: lateral and medial sites with peak densities, and a central site of least density in the medullary cavity. The bone mineral content(BMC) in grams per 2-cm cross section of bone was estimated using regression equationsderived by Ott et al. (1987).

Training Schedule

During the training phase (Phase B) of the study the horses alternated exercising three days per week on a high speed treadmill and 3 days per week on a mechanical walking machine. During the first week of training the horse’s treadmill exercise consisted of a 3 min walk (1.5 m/s), 3 min trot (4 m/s) and a 5 min walk (1.5 m/s). During weeks 2-4 of training treadmill exercise was increased to 3 min walking, 5 min trotting and 5 min walking. During weeks 3-8 of the training period the treadmill exercise consisted of a 3 min walk, 5 min trot, 1 min canter (8 m/s) and 5 min walk. Beginning in week 9 of the training phase the horses increased their 3 day per week treadmill regime to 3 min walking, 5 min trotting, 2 min cantering (8 m/s) and 5 min walking. During weeks 1-8 the horses walked for 30 minutes on the mechanical walker 3 days per week. Week 9-12 they were walked 60 minutes per day on the walker 3 days per week.

Confinement Phase

At the conclusion of the training phase of the study the horses entered a confinement phase in which they were keep in box stalls 24 hours/day for a 4 week period. Bone density was estimated from dorsopalmar radiographs of MCIII at 0, 14 and 28 days of confinement.

Results and discussion

During the Phase A turn-out period the BMC of the Duraplex group increased and there was a trend (p=.08) for mean RBAE (figure 1) and BMC (figure 2) to be higher in the treated group, but these differences disappeared during Phase B when exercise on the treadmill and mechanical walker was introduced. When the horses were confined in stalls during mean RBAE and BMC were unchanged in the treated group, but there was a trend (p=.08) towards a drop in the control horses.

Figure 1. Mean RBAE (mm Al) Figure 2. Bone mineral content (g/2 cm)

The results of this study suggest that forced exercise on a treadmill and mechanical walker is adequate to maintain bone density in Thoroughbred horses. Total stall confinement, may lead to bone de-mineralization and Duraplex supplementation may attenuate this drop.


Inoue et al, 2006. The effect of milk basic protein supplementation on bone metabolism during training of young Thoroughbred racehorses. Equine Vet J Suppl 2006 Aug (36) :654.

Inoue et al, 2007. The effect of milk basic protein supplementation on bone metabolism in mature horses. Proc of Equine Science Symposium 2007 p229.

Ott, E.A., L.A. Lawrence, and C. Ice. 1987. Use of the image analyzer for radiographic photometric estimation of bone mineral content. In: Proc. 10th Equine Nutr. and Physiol. Symp., Ft. Collins, CO., p. 527.