Equine Athlete

No sweat

Understanding Anhidrosis in horses

Courtesy Palm Beach Equine Clinic

Top right: Dr. Bryan Dubynsky tests electrolyte levels by taking a blood sample. Below: A lack of or light sweating during or after exercise in warm weather may be a sign of anhidrosis.

Summer heat is in full force and with the unrelenting temperatures and high humidity comes an increased risk of anhidrosis. Anhidrosis is the inability to produce an adequate amount of sweat. Horses suffering from this condition are often called “nonsweaters.” Sweating allows the horse to thermoregulate and maintain a consistent internal temperature. Horses lose 65-70% of their body heat through sweating and the evaporation of sweat. When these regulatory mechanisms stop working, the horse may be at risk of hyperthermia (overheating) or heat stroke.

While there is no definitive cause of anhidrosis, it is believed to be triggered by overstimulated sweat glands. During hotter times of the year, the sweat glands can be put into overdrive and essentially start to shut down. Areas with humid climates also further reduce the amount of sweat that will evaporate and therefore pose an even bigger challenge for cooling down the horse. Signs of anhidrosis include: • A lack of sweating during and after exercise or in warm weather. Some horses may sweat very lightly or only in patches. Times when your horse should be lathered in sweat, such as during a summer

afternoon ride when all other horses are sweating, they may only be a little damp under the saddle pad. • Labored breathing with shallow, rapid breaths and flaring nostrils as the horse tries to release heat. An elevated respiratory rate for an extended period of time after exercise (typically longer than 30 minutes). • Poor-performance as they are lethargic or become easily and quickly exhausted during exercise. If untreated, this can limit a horse’s career potential. • A poor-quality coat, dry patches of skin or thinning of hair can be an early sign. • Poor appetite and not consuming water as usual.

Any horse can develop anhidrosis and in varying degrees of severity. There are no proven correlations between breed, age, sex or color as to which horse is predisposed to anhidrosis, although its more reported in horses with darker colored coats. The condition may occur suddenly, often with a big change in environment, or it can develop gradually over time. Horses raised in hotter climates have no advantage over the condition than those born in colder climates.

It is important to have a veterinarian diagnose non-sweating as they will be able to rule out any other conditions that may have similar signs. Your veterinarian will perform a full physical exam and can run diagnostic tests through injections of epinephrine or terbutaline to stimulate the sweat glands and measure the amount of sweat produced. The veterinarian can also test the horse’s electrolyte levels through taking a blood sample.

A non-sweater may only be able to exercise during early hours or late in the evening when temperatures are cooler.

There are many options for treating anhidrosis, but it can be a challenge to completely cure the condition. Some treatments may be successful for one horse and ineffective on others, with little scientific evidence. Several treatment options veterinarians, owners and managers have seen success with include: • Acupuncture treatment programs • The Chinese herbal medicine New Xiang Ru

San, which naturally promotes heat and fluid disbursement • Electrolyte, vitamin and salt supplements • Thyroid hormones • Giving the horse a dark beer

Again, it is vital a veterinarian is consulted before beginning any treatment plan. Until a successful treatment plan is in place, the horse will need to be carefully managed. Some options for keeping them cool include: • Adjust the horse’s training schedule so they are only exercised during early hours or late in the evening when temperatures are cooler. • Do not turn the horse out when the sun is strongest during the afternoon hours, and make sure they always have a shaded area when outside. • Make sure they have stall fans or misters to provide some relief. • As a last resort, the horse may need to be moved to an area with a cooler, less humid climate. This may allow their internal thermoregulatory mechanisms to restore and commence normal sweating.

If your horse isn’t sweating, be prepared to make changes in their management and adjust your expectations for that horse’s performance abilities and potential career. With early attention and careful management, you can keep your horse comfortable and prevent overheating.

If you are concerned your horse may be anhidrotic, call Palm Beach Equine Clinic at 561793-1599 or visit equineclinic.com to speak with a veterinarian.

Dr. Janet Greenfield Davis gives a horse an acupuncture treatment.