Walking On, Volume 8, Issue 9, Nov/Dec 2021 - Page 10

For the Health of It

Exhausted horse syndrome refers to a range of metabolic and physiologic conditions that may occur when horses become fatigued . Affected horses may display a decrease in energy , appetite , or appear stiff and weak . In serious cases , cardiac arrhythmias , shock , muscle damage , colic , and diarrhea may develop . Horses that are underconditioned , performing in endurance events , or exercised in hot or humid environments are at higher risk for exhaustion . If exercise is not immediately halted and treatment initiated , then life-threatening
10 • Walking On

Exhaustion In Horses

Reprinted with permission from Volume 30 , Number 4 of Equine Disease Quarterly
complications may occur .
Exhaustion may develop with any prolonged period of exercise such as endurance rides , threeday events , and extended trail rides . Many factors contribute to the potential for exhaustion . Differ- ent breeds are better suited to prolonged exercise while others excel at shorter , more high intensity work . The animal ’ s training and fitness ideally should be suited for the event they are participat- ing in , although even highly prepared animals may develop exhaustion . Any underlying disease , including lameness , anemia , and respiratory disease will increase the risk of fatigue .
Exhaustion is a multifactorial condition . Heat , electrolyte imbalance and energy stores may contribute . A large amount of heat is produced while exercising . Heat needs to be appropriately regulated and removed from an exercising animal via sweat and air movement . If heat is not removed , then the core body temperature steadily increases . Approximately 65 % of heat is lost via sweat , 25 % via respiratory evaporation , and the remaining 10 % via other mechanisms . This is made more difficult when the conditions include high heat and humidity or when the animal is dehydrated . Sweat contains important electrolytes such as sodium , potassium , calcium and chloride which are lost as the horse sweats . If electrolyte imbalances are not corrected , then serious derangements occur lead- ing to shifts in blood pH and cellular stability . The primary energy source for muscles is stored glyco- gen , which is a finite resource . Glycogen stores can be increased with training and exercise , but once depleted the muscle lacks a primary energy source and exercise will slow or stop .
Horses with exhaustion will have an increased heart rate , temperature , and respiratory rate . They may appear depressed , unwilling to eat and drink , and , in some cases , develop colic , shock , or lami- nitis . Horses that move with a stiff gait may have significant muscle damage and / or laminitis . These animals should not be forced to move if treatment can be provided on site . Affected horses are typi- cally dehydrated and blood work shows evidence of stress and electrolyte imbalances . Muscle enzyme values will be increased and often continue to in- crease as muscle damage continues . Kidney values , which reflect both dehydration and renal damage , may be elevated and urine may be significantly decreased in volume and dark brown / red in color . Genetic testing , muscle biopsy