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by Kim and Kari Baker


Mirror KB Equine Article Series

Heat Stress: Sultry Summertime Threat
Article and Photos by Kim and Kari Baker

     Under the relentless heat of the noonday sun, you leave the arena in disgust. Throughout the class your horse has responded poorly to your cues. Cues which you know he understands readily. Cues that he had responded well to earlier in the day and has repeated perfectly during many other shows. So what could be the problem?

     By general observation, your horse appears to be fine. You are unable to detect any apparent sign of lameness, colic, muscle stiffness or fatigue such as seen in cases of tying up. However, you do notice that he’s slightly sweaty, yet not as drenched in sweat as several of your friends’ horses.

     His breathing seems to be a little heavier and faster than usual after a normal workout, but you can’t identify any other outward signs of distress. Back in the show barn you proceed to examine your horse more carefully, taking his temperature and pulse rate, plus checking capillary refill time and hydration. From the information you have gathered, you now realize that your horse is in need of veterinary assistance.

     Heat stress, the term commonly used for both heat exhaustion and heat stroke, is triggered by hot humid weather, in combination with over exertion, excessive loss of body fluid, or poor ventilation. The malady occurs when a horse is unable to efficiently regulate his body temperature by dispersing internal heat through respiration and the evaporation of sweat on the surface of his skin. If the condition is not reversed without delay, the horse’s blood vessels will dilate, and without compensating with an increase in blood volume, the result will be circulatory collapse, shock, and death.

     Once a horse’s cooling system is disrupted and has succumbed to heat stress, treatment must be immediate. The primary objective is to re-hydrate the horse and reduce his body temperature. This can be accomplished by moving the horse into the shade and pushing oral fluids such as water and electrolytes. Spraying the horse’s entire body with water, as cold as possible and the use of ice packs on the head and legs is also beneficial. Applying cold water to his legs will constrict the vessels of the feet, which will in turn, help the circulatory system maintain adequate pressure for body functions. It is advisable to intermittently remove the warmed water from the horse’s coat with a sweat scraper and then resume with the cold water bath. Manually massaging the heavy muscles over the horse’s hips and shoulders can minimize the possible damage caused to the muscles from excessive heat and will also improve the circulation of the cooled blood from the horse’s head and legs. Depending on the severity of your horse’s condition, the veterinarian may choose to administer an isotonic saline solution by means of an IV. This will replace the fluids that were lost through sweat and respiration, increasing the volume of blood, which will aid in carrying internal body heat to the surface of the skin. Once the horse’s temperature has decreased to 102 degrees, full body water baths should be stopped to avoid causing shock. Hosing of the head, neck, and legs can still be beneficial while the horse’s body temperature is closely monitored. Full recovery may take up to 7-10 days. Once your horse has experienced heat stress he may be more susceptible to the condition for the remainder of the summer.

Preventing heat stress

When the heat index is extreme there are a number of things you can do to prevent heat stress in your horse.

1. When feasible, ride your horse in the cool hours of the day. If this isn’t practical, avoid putting your horse through an intense work out. Keep the training sessions as short and stress free as possible.

2. Furnish adequate water at all times. Your horse will require a minimum of 8 - 12 gallons of water per day. Also provide your horse with free access to trace-mineralized salt.

3. Avoid stabling the horse in hot, poorly ventilated stalls. When necessary use fans to help circulate air throughout the stall. Provide ample shade for horses in pasture with trees or run-in sheds.

4. Monitor your horse’s vital signs, during and immediately after a work out or performance event. Note any change in his vital signs that may indicate the onset of heat stress.

5. Administering an electrolyte replacer 1 - 2 hours before anticipated high performance activity will go a long way in keeping your horse hydrated as well as frequently offering him a drink of water, such as between each class during a horse show.

6. When possible, carefully acclimate your horse to work in hot humid weather a week or so prior to a scheduled event.

7. Properly cool out your horse before putting him in his stall or turning him out to pasture.

8. Avoid transporting horses during hot humid weather. If the horse must be transported try to plan the trip during the cool hours of the day. If the trip extends into the heat of the day be sure trailers are well ventilated and stop often to offer your horse a drink of water.

9. Any new social arrangement that may cause over excitement or stress should be avoided when the heat index is extreme. Several such situations to avoid are: weaning foals from their dams, breeding a mare and stallion, and introducing horses to new surroundings and/or new pasture mates.

10. Schedule any necessary veterinary procedures such as castrations or other elective surgeries during the cooler times of the day, and even more ideal, try to schedule them during the moderate seasons of the year.

Just as in people, heat stress in horses, is a critical life threatening emergency. Knowing how to recognize the early signs of heat stress and what emergency care you should provide, can mean the difference between your horse’s life or his death.

We would like to acknowledge the technical consultation and critique provided by Dr. Paul Schaumberg D.V.M of Kootenai Veterinary Service.

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