Written by Dr. Jessica Reynolds

2021-2022 Peterson Smith Equine Hospital + Complete Care Ambulatory Intern

What causes heat stress?

• More common in poorly conditioned horses that are overworked in hot and humid climates (Florida!), in conjunction with anhidrosis (not sweating), dehydration, or exhaustion syndrome.
• Horses that are confined in poorly ventilated areas (shipping).
• Healthy horses can also experience heat stress when the sum of temperature (in Fahrenheit) and humidity have a value of >180.
  • If horses are moved from cool to hot climate, several days are needed for the horse to acclimate to the change in temperature.
• Foals with Rhodococcus equi using a macrolide antibiotic (erythromycin) are also more prone.
• High fever (up to 106) in horses rarely ever cause heat stroke if due to a viral infection.

How to diagnose heat stroke/stress?

• History and clinical signs!
  • Increased respiratory rate, lethargy, decreased appetite, shade seeking.

Clinical signs of heat stress:

• Poor sweating response to anhidrosis (not sweating).
• Hot, dry skin
• Increased heart rate and respiratory rate
• Elevated rectal temperature (106-110).
• Prolonged capillary refill time, dark mucus membranes (gums).
• Depression, weakness.

What to do next:

• Decrease the body temperature:
  • The quicker treatment and more rapid cooling, the better the prognosis.
  • Move horses to a shaded, well-ventilated area with fans if possible.
  • Apply cold water or ice water hydrotherapy (cold hosing) to the entire body, focusing on the jugular groove and chest.
    • Continually scrape the water off the horse and reapply.
  • Can use alcohol over neck/jugular groove/chest area as well.
  • Offer water, can add electrolytes to encourage hydration.
  • Administer anti-pyretic (anti-fever) such as Flunixin Meglumine (Banamine), use the dosage as recommended by your veterinarian.
  • Restore blood volume:
    • Contact your veterinarian to provide IV fluid therapy as they deem necessary.
  • Bloodwork: Chemistry and CBC panel to evaluate organ functioning, and to see if further treatment is needed.

What NOT to do:

• Do not use any fabric (towels, cooling sheets, etc), they prevent the heat from leaving the body.
• Do not force the horse to walk, unless its to move into the shade/better ventilated area.
• Do not withhold water.
• Do not administer Dormosedan or Xylazine (sedatives), they can cause respiratory distress.

Reference:

• Divers, T.J. Orsini, J.A. (2014) ‘Equine Emergencies Treatment and Protocols Fourth Edition’ Elsevier