The bond between dogs and humans may be reflected in their hormones, suggests a study in Physiology & Behavior.

Researchers found that participating in competitive dog trials, increased levels of the stress hormone cortisol in the saliva of dog handlers and their dogs. Interestingly, elevated cortisol levels were most pronounced in teams of dogs paired with men.

Previous studies have shown dog owners’ emotional state can affect hormone levels in dogs. For instance, increased levels of oxytocin, sometimes called the “love hormone,” in puppy owners is often mirrored in their pets.

The study, at the University of Nebraska in Omaha, followed 58 people and 58 dogs participating in dog agility competitions, which are stressful events that require dogs to complete an obstacle course as quickly as possible without errors, guided by cues from their handlers. The handlers included 44 women and 14 men, 52 years old on average.

Saliva samples were collected from handlers and dogs before and after the trials and analyzed for cortisol in dogs and cortisol and testosterone in handlers. Handlers also assessed their dog’s personality and rated their performances during the trials. Handlers’ behavior toward their dogs following the competition was recorded.

Cortisol levels in men and their dogs were significantly higher post-competition compared with before the event. Cortisol levels in women handlers increased only slightly and didn’t change in dogs. Women may interact differently with dogs, which could affect their own and their dog’s physiological state, researchers said. Testosterone levels, although higher in men than women before the competition, were unrelated to cortisol changes. Cortisol levels in dogs were also unrelated to the sex of the dog and the handlers’ tone of voice or behavior toward their dogs.Dogs may have picked up odors or behavioral cues from handlers, such as body language, facial expressions or different types of touch, which served to transmit physiological states between humans and dogs, the researchers said.

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