Page 64 - July 2020

VETERINARY VIEWS
RECOGNIZING AND PREVENTING HEAT STRESS
When ambient temperature and humidity rise to certain levels, an exercising horse might be in danger of developing heat stress, especially when hot weather is coupled with arduous and/or pro- longed exertions. A hot day without humidity also poses a risk.
A horse demonstrating signs of heat stress – either subtle or obvious – could signal impend- ing metabolic collapse. If any of these signs
are seen, then it is necessary to stop the horse’s exercise immediately and begin implement- ing cooling strategies, described below. If the horse’s rectal temperature does not begin to return to normal within 15 minutes or so, a veterinarian should be contacted immediately.
Locomotion Abnormalities
• Flagging body posture under saddle
• Need to urge horse to
maintain speed
• Stride flattens out
• Poor impulsion
• Stumbling
• Ataxic (incoordination) or weak
Body Function Changes
• Waning or absent appetite
• Lack of thirst
• Reduced or absence of urination
• Reduced or absence of bowel movements
• Decreased intestinal sounds
Overt Problems
• Tying-up syndrome (myositis)
• Thumps (synchronous diaphragmatic flutter) • Colic
• Neurologic abnormalities
Attitude and Posture Changes
• Grumpy disposition when handled
• Grumpy when asked to perform
• Lack of alertness or interest in surroundings • Dull or glazed eyes
• Sagging or deflated posture at rest
• Wrinkled lips
• Ears at half-mast
• Anxious expression
VITAL SIGNS
In addition to your horse’s display of posture, attitude, mood and intake of food
and water, check vital signs to determine how well he is coping with the exercise demand and climate conditions of the day.
• Heart rate (or pulse): A horse’s pulse, or heart rate
(measured in beats per minute), informs about how well he’s recovering from exercise. The heart rate should return to about 60 to 64 beats per minute within 10 minutes of stopping aerobic exercise, but will take a bit longer with sprint and anaerobic efforts. Poor heart rate recovery may signal impending metabolic collapse due to the combined effects of energy depletion, electrolyte loss, and heat build-up in the muscles.
• Respiration: The respiratory rate (breaths per minute) should return to normal within 10 minutes of stopping aerobic exercise, and a bit longer following sprint workouts. If the heart rate returns to 60 bpm or below but the respiratory rate remains elevated, such an inversion does not necessarily imply the horse is in trouble. It means he needs help in ridding his body of the extra heat. If the horse is panting, there may be nothing abnormal about the horse other than having bigger, bulkier muscles than a leaner-muscled breed. In other cases, it is
a true reflection of limited fitness or being asked too much for the conditions of the day. Respiratory rate is a useful means of evaluat- ing a horse’s ability to cope with the exercise demand, the pace, and heat and humidity.
• Gum color and capillary refill time: Lift the horse’s upper lip to evaluate the gums – they should be moist and pink, like what you
see under your pinky nail. Press gently to blanche away the color and the gums should pink up again within two seconds. Slow capillary refill time and/or lack of moistness indicate dehydration.
• Skin turgor: To roughly estimate dehydra- tion, pinch a fold of skin on the point of the shoulder or the upper eyelid. It should snap back into position immediately. If it doesn’t return to its normal position and remains “tented,” the horse is likely 3-5% dehydra-
by Nancy S. Loving, DVM
Signs of heat stress may include:
Stumbling Grumpy disposition when handled Colic
62 SPEEDHORSE July 2020