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Nature of Exercise: Primarily depends on aerobic metabolism, which is inefficient; 75%–80% of energy produced is converted to heat.
Nature of Exercise: Primarily depends on aerobic metabolism, which is inefficient; 75%–80% of energy produced is converted to heat.
- Fatigue Drivers:
- Substrate Depletion: Hypoglycemia and the depletion of glycogen stores in the muscle and liver.
- Thermoregulatory Demand: High ambient temperatures and humidity increase the risk.
- Physiological Cost: Occurs when the costs of sustained submaximal exercise exceed the horse's ability to maintain fluid and electrolyte balance.
At-Risk Groups: Horses competing in endurance rides, 3-day eventing, or combined driving.
At-Risk Groups: Horses competing in endurance rides, 3-day eventing, or combined driving.
Pathophysiology (Exhausted Horse Syndrome)
Pathophysiology (Exhausted Horse Syndrome)
- Fluid Loss: Horses can lose 10–15 L/hour of body fluids through sweat, potentially losing up to 10% of their body weight (40 L).
- Electrolyte Depletion: Equine sweat is hypertonic, leading to dramatic losses of sodium, potassium, chloride, calcium, and magnesium.
- Perfusion & Organ Impact: Decreased blood volume (hypovolemia) leads to hypoxia and potential multiorgan failure, damaging the kidneys, GI mucosa, and hoof lamina.
- Acid-Base Derangements:
- Endurance (Aerobic): Predominantly metabolic alkalosis due to chloride and potassium loss.
- High-Intensity Bursts (Anaerobic): Initial metabolic acidosis from lactate, which often resolves into alkalosis during recovery.
Clinical Findings:
Clinical Findings:
- Dehydration & Perfusion: Notable perfusion abnormalities and listlessness.
- Neuromuscular: Ataxia, gait alterations, recumbency, and synchronous diaphragmatic flutter.
- Myopathy: Hard muscle bellies and pain upon palpation.
- Vital Signs: Elevated rectal temperature (≥ 42°C [107.6° F]), and persistent tachycardia/tachypnea despite rest.
- Gastrointestinal: Abdominal pain (colic) and ileus.
Treatment Protocols
Treatment Protocols
- Rapid External Cooling:
- Move to shade; use cool-water sponge baths, hosing, or misting fans.
- Crucial Step: Use a sweat scraper to remove water from the coat to prevent it from acting as an insulating layer.
- Fluid Therapy:
- Oral: Isotonic balanced electrolyte solutions via nasogastric tube (if normal gut sounds are present).
- Intravenous (IV): Preferred for severe cases; involves balanced electrolyte shock doses often supplemented with calcium gluconate and dextrose.
- Supportive Medications:
- NSAIDs: For muscle pain and colic (given with fluids to protect kidneys).
- Glucocorticoids: Dexamethasone for cerebral edema.
- Others: Phenothiazines for anxiety, anticonvulsants, or heparin for coagulopathies.
Prevention Strategies:
Prevention Strategies:
- Hydration Management: Ensure adequate hydration before an event, especially after transport.
- Access to Resources: Provide continuous access to fluids and electrolytes during and after exercise.
- Supplementation: Use of oral electrolytes and glucose before/during competition when permitted by regulations.
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