Page 60 - 2018 Barrel Stallion Register

“. . . exertional rhabdomyolysis (ER) is simply a clinical description of horses that develop muscle damage and pain with exercise. Just like the term colic, there can be many different causes.”
TYING UP
by Heather Smith Thomas
Muscle problems are fairly common in athletic horses. Muscle pain and cramping associ- ated with exercise has been recognized for
more than 150 years and various terms have been used to describe it (azoturia, Monday morning disease, etc.). In recent years, veterinary researchers found there are several forms of tying up with different possible causes, and it is generally termed exertional rhabdomyolysis.
SPORADIC TYING UP IS NOT A GENETIC DISORDER
Some horses have sporadic muscle damage that doesn’t occur very often. “The muscle is basically nor- mal, but with some exercise regimes or dietary insuffi- ciencies individual horses may develop muscle pain and cramping. There is probably no underlying abnormal- ity or functional defect in their muscles--just an imbal- ance that needs corrected. Those horses usually do fine after they get rested and get over the cramping,” says Valberg. The horse may have done something out of the ordinary that day which was too much for their conditioning. For instance, they may have strained one group of muscles, or muscles over the whole body, if they were exercising during extremely hot and humid weather and have electrolyte disturbances.
“If diet isn’t balanced (not enough vitamin E
and selenium, or inadequate salts during hot, humid weather) this can lead to muscle problems. In these cases, after a tying-up episode, if you make sure the horse has a regular training regime, the amount of exercise is not excessive, and diet well balanced (with electrolytes, vitamins and minerals), and not too high in grain, they do fine if they are rested and then put back into work. They won’t have another episode of tying up,” she explains.
“I think there are also episodes in certain horses of simple muscle cramping that is not exertional rhabdomyolysis. A cramp occurs because the nerve fires and the muscle contracts and then doesn’t relax, but the muscle isn’t damaged. The muscle becomes tense and stiff (like a muscle cramp in humans), but then the horse is able to walk out of it. If the muscle enzymes like CK (creatine kinase) or AST (aspartate
Stephanie Valberg, DVM,
PhD, ACVIM (McPhail
Chair in Sports Medicine,
Professor, Michigan State
University) has been doing
research on muscle problems
in horses since the 1980’s.
“When we first started
research on tying up, there
was a general assumption that
all horses tied up for the same
reason. The term exertional
rhabdomyolysis (ER) is simply a
clinical description of horses that develop muscle dam- age and pain with exercise. Just like the term colic, there can be many different causes,” says Valberg.
ER is broken down into two categories: sporadic and chronic. The latter condition is due to specific inherited abnormalities and can be broken down further into two distinct types--polysaccharide stor- age myopathy (PSSM) in Quarter Horses, warm- bloods and draft breeds (breeds with heavy muscles), and recurrent exertional rhabdomyolysis (RER)
in Thoroughbreds, Standardbreds, racing Quarter Horses, Arabians and Warmbloods.
Dr. Stephanie Valberg, DVM, PhD, ACVIM
Signs of Exertional Rhabdomyolysis (ER): Muscle stiffness, cramping, pain, muscle fasciculation exercise intolerance, firm muscles, lameness, discolored brown urine (myoglobinuria), or progressive weakness, and suspect PSSM
BREED OF THE HORSE AFFECTED?
Quarter Horse, Paint, Appaloosa or cross
Draft Horse, Draft Cross
Rocky Mountain Horse, Tennessee Walking Horse, Morgan, Haflinger
Warmblood
Thoroughbred, Arab, Standardbred, other light horse breed
AND
Submit whole blood or hair roots for genetic testing for PSSM mutation as well as modifying gene mutation
Submit whole blood or hair roots for genetic testing for PSSM mutation
Submit whole blood or hair roots for genetic testing for PSSM mutation
PSSM mutation positive
Follow dietary and management recommendations
PSSM mutation negative
58 SPEEDHORSE
EQUINE HEALTH