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Chill Out: Researchers Compare Cooling Methods For Equine Athletes

Elite athletes like racehorses and three-day event horses sometimes exercise on hot, humid days, often resulting in high body temperatures that must be lowered quickly before heat-related stressors set in. While much research has been performed on effective cooling strategies, a new study compared several different cooling methods.^*

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Thoroughbreds were exercised on an inclined treadmill until the pulmonary artery temperature reached 107.6 degrees Fahrenheit. One of five cooling methods was then implemented. The methods included:

Walking on a treadmill with one commercial fan placed 6.5 feet in front of the horse set at low velocity to simulate the breeze that would occur if walked outside (control);
Walking on a treadmill with two fans placed 13 feet in front of the horse set at almost twice the airflow of the fans used in the control;
Cooling with intermittent application of cold water (4.2 gallons at 50 degrees Fahrenheit) every three minutes on its body behind the neck, scraping as much water as possible after dousing; two cycles of dousing performed with return to treadmill walking and two low-speed fans in the interim;
Cooling with intermittent application of cold water (16 liters; 50° F or 10° C) every three minutes on its body behind the neck with no scraping; two cycles performed with return to the treadmill and two low-speed fans in the interim; and
Showering continuously with tap water (78.8 degrees Fahrenheit) for 30 minutes with no return to the treadmill.

To determine the most effective cooling method, researchers measured the time necessary for the pulmonary artery temperature to return to 102.2 degrees Fahrenheit or lower, and recorded the rectal temperature at 30 minutes after onset of cooling.

The researchers concluded that showering the horse continuously with a large volume of tap water resulted in the most rapid decrease of both pulmonary artery and rectal temperatures, signifying its effectiveness as a way to achieve cooling in hot, humid conditions.

Sweat production goes hand-in-hand with exercise. Multiple factors determine how much sweat is lost doing any exercise bout (heat, humidity, and work intensity, for example). Light exercise with minimal sweating may induce a sweat loss of 1 quart to 1 gallon, while high-performance horses at the peak of exertion may have losses of 12.25 to 3 gallons.

Because large quantities of electrolytes are lost in sweat, electrolyte supplementation becomes a key factor in managing the diets of performance horses. Choose research-proven electrolytes formulated by specialists in equine nutrition and exercise physiology.

Electrolyte supplementation is not season-specific. Well-formulated electrolytes should be used whenever horses sweat on a daily or near daily basis, no matter the season.

^*Takahashi, Y., H. Ohmura, K. Mukai, T. Shiose, and T. Takahashi. 2020. A comparison of five cooling methods in hot and humid environments in Thoroughbred horses. Journal of Equine Veterinary Science 91:103130.

Genetic Marker Tied To Anhidrosis Discovered; Similar To Cystic Fibrosis

Sweating is a critical tool to keep horses comfortable and healthy, but chronic idiopathic anhidrosis, a dangerous equine condition can impede their natural cooling mechanism and cause performance and health issues. For the first time, University of Florida's Institute of Food and Agricultural Sciences (UF/IFAS) researchers have identified genomic markers that cause the potentially fatal condition.

The genomic mapping study gave researchers a discovery-based approach to attacking this disease, pushing aside prior assumptions about the disease's causes. A team of UF scientists from the Genetics Institute and the College of Veterinary Medicine used genetic markers like signposts, looking for the common genomic markers found in horses that had chronic idiopathic anhidrosis disease. These genetic signposts pointed to a defective potassium transporter that likely hinders sweat function.

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“Now that we know which biological pathways cause the condition, we hope to design specific strategies to intervene,” said Samantha Brooks, UF/IFAS associate professor of equine physiology. “We found that this disease has similarities to cystic fibrosis which has many drug treatments available and in development. Knowing this, we can start to consider ways to treat these horses that suffer from this condition, helping them sweat more normally over longer periods of time.”

Genetic mutations leading to cystic fibrosis also impact ion channels and gave researchers some clues as to how this particu.lar defective potassium transporter might work. Additional research is needed to fully understand, but researchers found a change in the protein that alters when this ion transporter turns on and off. The stress of the sweat gland attempting to function with this faulty transporter likely destroys the ability to sweat over time.

“Using histology, the study of the structure of the tissues, previous work found that the sweat glands become damaged after horses live with chronic idiopathic anhidrosis over long periods of time,” Brooks said. “That is why we have not been successful in reversing the disease and restoring sweat function. Trying to sweat without a functional ion transporter could be the cause of the damage to the cells in the sweat gland. We may not be able to reverse that.”

Having chronic idiopathic anhidrosis is like driving a car on a flat tire, Brooks explained. Over time, a horse living with this disease experiences impacts to their overall health beyond the inability to sweat. Living with the condition becomes a quality-of-life concern and unlike other kinds of anhidrosis, chronic idiopathic anhidrosis cannot be solved quickly or cured.

“The saddest part about this disease is that we do not have any specific way to treat the condition right now,” Brooks said. “We can see what is happening and try to address the symptoms but because we do not know exactly what is causing it, we cannot attack the disease. So far, no supplements or medications have been tested and proven to work in a scientific study.”

Most chronic idiopathic anhidrosis horses sweat normally when they are young, but their cells accumulate damage over time, especially in extreme environments like Florida. Older horses experience more severe clinical signs such as critical hyperthermia as they lose more sweat gland function over time.

“We also do not understand the severity aspect,” said Laura Patterson Rosa, animal science graduate student and lead author of the study published in the Journal of Investigative Dermatology. “We don't understand why some horses have it worse than others. Even if it is chronic, the severity differs.”

In their study, scientists were surprised to find the genetic marker that causes chronic idiopathic anhidrosis is a common marker, particularly in sport-type horses like Quarter Horses and Thoroughbreds.

“I think there are a lot of horses out there struggling to live with the early stages of this disease, but owners and caretakers are just not aware of it,” Brooks said. “Long periods of hot humid weather here in the southeastern U.S aggravate the condition, increasing the chances an owner will notice the problem, but it can be just as much of an issue for horses in more northern locations. You may not think of places up north as having a hot summer that would make it hard for these horses to live, but if a horse has chronic idiopathic anhidrosis it might just take a single day in the 90s to trigger an episode of overheating. That can be very startling to their caretakers, and miserable for the horses. Especially if they live in a climate where those hot days are rare.”

The first signs of an insufficient sweat response and poor cooling are often a decrease in performance of the horse. They may get more tired during exercise, and although they still have some ability to sweat, it is often difficult for caretakers to accurately assess the volume of sweat they are producing. Over time as their ability to sweat decreases, their coats become dry and during overheating episodes it becomes more noticeable. Another side effect includes skin flakiness, rashes and an overall poor hair coat since the sweat glands are no longer distributing healthy oils to the skin.

“If your horse is one of the 2 percent affected by this disease, this diagnosis can be an absolute disaster,” Brooks said. “Still, I think a lot of these horses are probably out there doing the best they can. They may have slightly decreased performance at first or become a bit lazy in the summer. They are often confused for horses that have allergies, asthma or a respiratory infection because they pant to cool themselves. At first glance, they look as if they are struggling to breath, but really, they are struggling to cool themselves.”

Horse owners who suspect their horse has chronic idiopathic anhidrosis should regularly take the animal's temperature and consult their veterinarian. It may appear that the horse has a fever, but in reality, their basal body temperature is elevated during hot times of day because they cannot regulate it on their own through sweating. Taking their temperature regularly can be a critical component for managing this disease and can help horse owners monitor how well efforts to help keep their horse cool are working and is an important weapon to attack this disease.

“This is a very dangerous disease,” Brooks said. “We often see sweating as a nuisance, but we forget that hyperthermia can be a very life-threatening emergency. This is the time of year, when temperatures start to rise, it is important to revisit this idea and increase awareness among horse owners and caretakers about the condition.”

Horses that have not previously struggled to stay cool and perform may still have issues in the future. As the disease progresses each year and the climate continues to warm, chronic idiopathic anhidrosis is a condition that could be diagnosed more often and become worse for those horses already affected with the disease.

Looking ahead, the research team would like to launch a new project, using samples from horses with and without the disease to measure how much of this disease is due to changes in the function of this particular potassium transfer problem compared to other factors, like the environment. Developing therapies to treat or cure chronic idiopathic anhidrosis and tests to detect a propensity for the condition are future goals as well.

“In our first study we went out and found horses with chronic idiopathic anhidrosis so we would love to measure how much of this disease is due to the potassium transporter and how many horses carry this variant,” Brooks said. “The next step, in collaboration with our colleagues at the UF college of veterinary medicine and pharmacy, will be to see if we can find a compound developed for humans that alters potassium transfer, potentially offsetting the genetic factors contributing to chronic idiopathic anhidrosis in the horse, and administrable in a way that is feasible and economical in such a large animal.”

“Through directed genomic selection, we can eliminate chronic idiopathic anhidrosis from the horse population,” Rosa said. “But that will take time and further research.”

Sun Worshiper Or Shade Seeker? No Common Denominator For Hot Horses

Though most humans seek shade on swelteringly hot days, horses don't necessarily feel the same way. Even when provided with a respite from the sun in the form of a run-in shed or shade trees, not all horses will use it, though most welfare guidelines recommend offering a horse a place to get out of the sun.

Drs. Iwona Janczarek, Anna Stachurska, Izabela Wilk, Anna Wiśniewska, Monika Różańska-Boczula, Beata Kaczmarek, Witold Kędzierski and Jarosław Łuszczyński created a study to test horses' preference for shade, sun or a mist curtain, which offers immediate cooling capabilities.

The team used 12 Warmbloods that were normally kept in stalls for the study. They turned out each horse for 45 minutes on a sandy paddock on a day when temperatures were between 84 and 89 degrees Fahrenheit and humidity was 42 percent. Almost half the paddock was covered in shade and there was a mist curtain in one corner.

The research team monitored heart variables to determine if the horses' behavior or emotional states were affected when they stood in different areas of the paddock. The scientists found that the horses had no strong preference on the amount of time spent in a particular area.

The horses showed slightly heightened relaxation when standing under the mist curtain, but they displayed similar levels of emotional arousal in all three areas. They showed no signs of overheating when standing in the sun.

The team suggests that additional studies be completed that focus on longer periods of turnout. The ability to choose between sun and shade may be crucial for maintaining body temperature, so the provision of shade for equine welfare is reasonable, they conclude.

Read the full study here.

Are Hot And Cold Therapies Helpful For Tendon Troubles?

Owners of horses with tendon injuries are often told to cold hose their horse's leg to try to bring down inflammation. Occasionally heat therapy is recommended to improve the flexibility and extensibility of tendon tissue.

While human therapy often combines hot and cold therapy for an injury, it's not often done in equine veterinary medicine. Drs. Kevin Haussler, Shana Wilde, Michael Davis, Ann Hessa and Wayne McIlwraith wanted to determine if cycling between hot and cold therapies was possible, and if it might assist injured horses.

Called “contrast therapy,” the goal is to increase blood circulation using cold and hot therapies to force the injured area to cycle between vasodilation and vasoconstriction. For cold therapy to be of value, tissue temperature must be reduced to 50 to 59 degrees Fahrenheit. However, cold therapy generally doesn't penetrate beyond one inch of tissue, no matter how long it is applied. To be beneficial, heat therapy must get the tissue temperature above 104 degrees F, but stay below 122 degrees F to not cause damage.

For the study, the research team used four horses with no tendon issues. They placed temperature probes on the horse's skin and implanted them deeply in the subcutaneous tissue near the deep digital flexor tendons and near the superficial digital flexor tendons. This allowed the tendon tissue to be cooled to less than 45 degrees F and warmed to more than 118 degrees F. Each cycle lasted 15 minutes; each session applied three hot and three cold cycles for approximately two hours per session.

The scientists reported that the device was able to achieve consistent hot and cold temperatures in the superficial tissues, but could not reach the target temperatures in the subcutaneous tissue near the deep digital flexor tendons consistently. More studies will determine if longer treatment times or different hot and cold application ratios might allow the deep digital flexor tendon tissues to reach therapeutic temperatures.

Read the article here.