Page 906 - Adams and Stashak's Lameness in Horses, 7th Edition
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872 Chapter 7
PSSM; however, the amount of starch and sugar can Intramuscular injections of vitamin E and selenium
vary widely, as can the type of fat. Not all of these feeds are used in an attempt to prevent RER. Ensuring ade
VetBooks.ir equine feed products is not listed on the feed tag, and ciated with IM injections.
quate oral intake may prevent the muscle soreness asso
are equally effective. At present, the NSC content of
Some mares appear to exhibit signs of ER during
consultation with the feed manufacturer is necessary to
obtain this information. Nutritional support is available estrus, and it may well be beneficial in these horses to
through most feed manufacturers in designing an appro suppress estrus behavior using progesterone injections.
priate diet. There are published peer‐reviewed studies to Testosterone and anabolic steroids are used at race
show the beneficial effect of one commercial diet on tracks to prevent signs of RER, but the efficacy has not
both RER and PSSM. 55,59 been evaluated.
Supplements Adjunct Therapies
Horses require daily dietary supplementation with Massage, myofascial release, mesotherapy, stretching,
sodium and chloride either in the form of loose salt and hot/cold therapy performed by experienced thera
(30–50 g/day) or a salt block. Additional electrolyte pists may be of benefit in individual cases of ER.
supplementation is indicated in hot, humid conditions.
Some studies suggest that electrolyte imbalances, as
reflected by low urinary fraction excretion of sodium or References
high dietary excretion of phosphorus, may contribute 1. Aleman M, Brosnan RJ, Williams DC, et al. Malignant hyperther
to ER, although others have not found a consistent mia in a horse anesthetized with halothane. J Vet Intern Med
abnormality. 28,29 2005;19:363–366.
A number of supplements are purported to decrease 2. Aleman M, Nieto JE, Magdesian KG. Malignant hyperthermia
lactic acid buildup in skeletal muscle of ER horses. These associated with ryanodine receptor 1 (C7360G) mutation in
Quarter Horses. J Vet Intern Med 2009;23:329–334.
include sodium bicarbonate, B vitamins, branched‐chain 3. Annandale EJ, Valberg SJ, Essen‐Gustavsson B. Effects of submax
amino acids, and dimethylglycine. Because lactic acido imal exercise on adenine nucleotide concentrations in skeletal
sis is no longer implicated as a cause for ER, it is difficult muscle fibers of horses with polysaccharide storage myopathy.
Am J Vet Res 2005;66:839–845.
to find a rationale for their use. 4. Bain FT, Merritt AM. Decreased erythrocyte potassium concen
tration associated with exercise‐related myopathy in horses. J Am
Vet Med Assoc 1990;196:1259–1261.
Medications 5. Baird JD, Valberg SJ, Anderson SM, et al. Presence of the glycogen
Low doses of acepromazine prior to exercise have synthase 1 (GYS1) mutation causing type 1 polysaccharide stor
been used in RER horses prone to excitement. A dose of age myopathy in continental European draught horse breeds. Vet
Rec 2010;167:781–784.
7 mg IV 20 minutes before exercise is reported to make 6. Bedford HE, Valberg SJ, Firshman AM. Early diagnosis and treat
horses more relaxed and manageable. Reserpine and ment of muscle atrophy and weakness associated with vitamin E
24
fluphenazine, which have a longer duration of effect, are deficiency. J Vet Intern Med 2010;24:712–712.
also used for this purpose. Horses given fluphenazine 7. Beech J, Fletcher JE, Lizzo F, et al. Effect of phenytoin on the clini
cal signs and in vitro muscle twitch characteristics in horses with
may occasionally exhibit bizarre behavior. Use of tran chronic intermittent rhabdomyolysis and myotonia. Am J Vet Res
quilizers may only be necessary when horses are in their 1988;49:2130–2133.
initial phase of training and accommodation to a new 8. Beech J, Lindborg S, Fletcher JE, et al. Caffeine contractures,
2+
environment because they obviously cannot compete on twitch characteristics and the threshold for Ca(2+)‐induced Ca
release in skeletal muscle from horses with chronic intermittent
these medications. rhabdomyolysis. Res Vet Sci 1993;54:110–117.
Dantrolene sodium acts to decrease release of cal 9. Borgia L, Valberg S, McCue M, et al. Glycaemic and insulinaemic
cium from the calcium release channel in skeletal mus responses to feeding hay with different non‐structural carbohydrate
cle and is used to treat MH. Dantrolene given to horses content in control and polysaccharide storage myopathy‐affected
horses. J Anim Physiol Anim Nutr (Berl) 2011;95:798–807.
with RER 90 minutes before exercise prevented abnor 10. Cardinet GH, Littrell JF, Freedland RA. Comparative investiga
mal elevations in CK following exercise. A dose of tions of serum creatine phosphokinase and glutamic‐oxaloacetic
52
800 mg of dantrolene was given to Thoroughbred transaminase activities in equine paralytic myoglobinuria. Res Vet
horses in the United Kingdom 1 hour prior to exercise Sci 1967;8:219–226.
and resulted in significantly lower post‐exercise CK 11. Carlson GP. Medical problems associated with protracted heat
and work stress in horses. In Proceedings of the Fifth Annual
activity than a placebo. It must be given 60–90 min Meeting of the Association of Equine Sports Medicine, Reno,
19
utes prior to exercise and horses do not need to be Nevada, 1985;84–99.
fasted. 51 12. Carlson GP. Synchronous diaphragmatic flutter In Current
Phenytoin (1.4–2.7 mg/kg PO BID) acts on a number Therapy in Equine Medicine, 2nd ed. Robinson NE, ed. W.B.
Saunders Co., Philadelphia, 1987;485–486.
of ion channels within muscle and nerves, including 13. Cole FL, Mellor DJ, Hodgson DR, et al. Prevalence and demo
sodium and calcium channels. Therapeutic levels vary, graphic characteristics of exertional rhabdomyolysis in horses in
so oral doses are adjusted by monitoring serum levels to Australia. Vet Rec 2004;155:625–630.
7
achieve 8 μg/mL and not to exceed 12 μg/mL. Drowsiness 14. Cumming WJKF JJ, Hudgson P, Mahon M. Color Atlas of Muscle
Pathology. Mosby‐Wolfe, London, UK, 1994.
and ataxia are evidence that the dose of phenytoin is too 15. De La Corte FD, Valberg SJ, MacLeay JM, et al. Developmental
high and the dose should be decreased by half. Initial onset of polysaccharide storage myopathy in 4 Quarter Horse
dosages start at 6–8 mg/kg orally twice a day for 3–5 foals. J Vet Intern Med 2002;16:581–587.
days. If the horse still experiences rhabdomyolysis but is 16. Divers TJ, Mohammed HO, Cummings JF, et al. Equine motor
neuron disease: findings in 28 horses and proposal of a patho
not drowsy, the dose can be increased by 1 mg/kg incre physiological mechanism for the disease. Equine Vet J 1994;26:
ments every 3–4 days. 409–415.
