As the director of the Penn Vet Working Dog Center, Cynthia Otto sees that, because working dogs are selected for high motivation, their drive can override physiological signs that they’re getting too hot. She says a search dog working in a humid environment or a police dog tracking a criminal could be at risk of exertional hyperthermia, an exercise-induced increase in core temperature above the baseline.
“Dogs don’t sweat, and they rely on panting; that’s really got some serious limitations. Once they reach a point of excess heat, they can’t continue to cool, and they can go from looking fine to collapsing. Once they develop full-on heat stroke, they have about a 50% survival rate,” Otto says. Heat-induced injuries are the most common non-traumatic cause of death for law enforcement and military dogs, who may be in an environment with limited resources for cooling.
But in a new study Otto and other researchers from the University of Pennsylvania School of Veterinary Medicine have identified an effective cooling method for field situations: Training dogs to voluntarily dunk their heads into 22°C water. Their findings are published in the Journal of the American Veterinary Medical Association.
They found that, among four cooling protocols tested, this one produced the lowest average core temperature in the five minutes after exercise. It was the only intervention to decrease core body temperature in the first 30 seconds, and it led to the lowest temperatures six to 40 minutes after the intervention.
“Voluntary head dunking is an invaluable tool in preventing exercise-induced hyperthermia or exercise-induced heat stress, and that can save lives,” says Otto, senior author on the paper.
The other three protocols involved securing two ice packs on a collar around the dog’s neck, putting a wet towel around the neck, and placing two wet towels under the dogs’ armpits.
The researchers conducted a randomized study in which 12 mentally and physically healthy dogs between eight months and 8 years of age underwent a cooling protocol after exercise. The dogs were stopped either after they exercised for 10 minutes, hit a core body temperature of 40.6°C, or exhibited two or more signs of heat stress, such as an elongated and flattened tongue or retracted ears. Each dog cycled through all protocols, with a separation of at least 48 hours in between. (Researchers demonstrate the voluntary head dunk in a video.)
Before the study, all dogs were trained to fetch a toy or food from the bottom of a bucket of water. Each study day consisted of a physical exam by a veterinarian, warm-up exercises, and a recall test that involved the dog running for its preferred toy between two people 25 meters apart. Afterward came the designated cooling intervention and a 40-minute cooling period.
The researchers activated accelerometers, heart rate monitors, and ingestible core temperature sensing capsules at the start of each day, and they took readings of core body temperature every minute of exercise to ensure the dogs’ body temperatures did not exceed the designated safety cutoff temperature.
Fourth-year Penn Vet student Sara Parnes, first author on the paper, explains that this study builds on a previous study she worked on with Otto in 2022. In that study, they found that partial water immersion cooled dogs faster than applying isopropyl alcohol to paw pads, and both methods were more effective than doing nothing.
“We wanted to build on that. Not every handler’s going to have access to a large pool of water,” Parnes says. “Depending where they are, like an earthquake scene or anywhere the dogs will be working, we want to have field-applicable things that they can use on the go. Most people carry towels and bottles of water, and there are usually ice packs in first aid kits.”
In a review of the literature, Parnes found retrospective studies looking at the temperature of dogs arriving at a hospital but no studies looking at different methods to cool dogs that are field-applicable.
Otto says one of her inspirations was a December 2022 trip to Zambia to work with conservation dogs, who are trained to detect contraband—such as smuggled ivory and pangolin scale—and to track poachers. “It gets really hot there, and they definitely can’t go swimming because there’s crocodiles and hippos and things,” Otto says. She tried the head dunk in the field and realized dogs could learn it in five minutes, but she didn’t measure temperature at that point.
The study’s findings are applicable not only for working dogs but also for pets. Otto notes that short-nosed dogs like the French bulldog, the most popular breed in the United States, have more difficulty getting rid of heat through panting and therefore take much less exertion to hit a breaking point. She adds that, when it comes to body temperature, there is no “magic number” to predict susceptibility to heat stress or heat stroke.
Parnes says that from working on these two studies and getting questions about her research from dog-owning friends she thought about how people don’t realize how common heat stroke is in pets. “Having owners be aware that you can do things at home to lower their body temperature and potentially save their lives is something that is very important for many pet owners to know,” she says.
Cynthia M. Otto is a professor of working dog sciences and sports medicine and director of the Penn Vet Working Dog Center at the University of Pennsylvania School of Veterinary Medicine.
Sara C. Parnes is a fourth-year student at Penn Vet.
The other co-authors are Penn Vet’s Amritha Mallikarjun, Meghan T. Ramos, and Tina R. Capparell.
This research was supported by the American Kennel Club Canine Health Foundation (Grant 03077-A).
