Prevention of Fatigue in Horses

Physiological Adaptations: Increases maximal oxygen transport, cardiac stroke volume, muscle capillary density, circulating blood volume, and total hemoglobin content.

Cellular Changes: Leads to muscle cell hypertrophy and increased concentrations of mitochondria.

Sport-Specific Adaptations:

• Sprint Training: Decreases slow-twitch muscle fibers and modulates electrolyte changes (decreases potassium efflux) to delay fatigue.

• Endurance Training: Increases the oxidative capacity of fast-twitch muscle fibers.

Intensity Thresholds: Significant adaptations in fast-twitch fibers and buffering capacity only occur at training intensities >80% of maximal oxygen uptake (VO₂ max).

Heart Rate: Monitors should target ~90% of maximal heart rate (typically 210–240 bpm) to reach the 80% VO₂ max threshold.

Blood Lactate: Measuring plasma lactate after exercise (target range of 4–10 mmol/L) helps confirm appropriate training intensity.

Primary Benefits: Increases muscle temperature, accelerates oxygen uptake, and enhances aerobic metabolism to decrease lactate accumulation.

Versatility: Effective whether the intensity is low (5–10 min at 50% VO₂ max) or high (1 min at 115% VO₂ max).

Application: Crucial for increasing time to fatigue in high-intensity racing (e.g., Quarter Horse, Thoroughbred, Standardbred).

Bicarbonate ("Milkshaking"):

• High Dosage (1 g/kg): Administered via nasogastric tube; has been shown to increase time to fatigue.

• Low Dosage (0.6 g/kg): Does not appear to effect the metabolic response or delay fatigue.

• Regulatory Note: This practice is banned by many racing administrations.

Pre-Exercise Hydration: Hyperhydration via oral electrolytes or saline helps expand and conserve plasma volume during the event.

Intra-Exercise Hydration: Maintaining euhydration (normal hydration) with water or carbohydrate-electrolyte solutions improves perfusion and sweating while decreasing heat storage.

Meal Timing: Avoid large meals 1–2 hours before intense exercise, as they decrease plasma volume and shift fluids to the GI tract.

Fiber Intake: High-fiber feeds act as a critical reservoir for water and electrolytes to replace sweat losses.

Fat Supplementation:

• Dosage: Adding vegetable oil at 10%–12% of the total diet.

• Benefits: Spares glycogen and glucose by increasing fat utilization; reduces CO₂ production and improves thermoregulation.

Glucose: Supplemental glucose (e.g., via IV infusion) prolongs endurance, increases glucose availability, and lowers core temperature.

Glycogen: Replenishment after intense exercise can take up to 48 hours.