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Dogs' Hormones Adjust to Match Those of Owners

Dogs connect so deeply to people that their hormones synchronize with ours.

The bond between dogs and humans is so deep that dog hormones actually synchronize to match those of their owners and handlers, a new study finds.

The study, which has been accepted for publication in the journal Physiology & Behavior, adds to the growing body of evidence that dogs and humans connect at both conscious and subconscious levels that can impact their core biochemistry.

As for why this might happen, lead author Alicia Phillips Buttner told Discovery News, "Given that both humans and dogs are such highly social species, synchronization of hormonal states could aid in social communication and cooperation."

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Buttner, a researcher in the Department of Psychology- Neuroscience & Behavior at the University of Nebraska at Omaha, conducted the study with colleagues Breanna Thompson, Rosemary Strasser and Jonathan Santo. The team took saliva samples from 58 male and female dogs and their handlers (44 women and 14 men) before and after dog agility competitions around the Midwest. The researchers also gathered information about the dogs and handlers, and observed how the pairs interacted after the competitions.

The scientists determined that levels of the hormone cortisol in the dogs' saliva mirrored those of their handlers.

"Although the public often associates cortisol with stress or distress, elevated cortisol levels during a competition may be reflective of excitement, arousal or physical exertion," Strasser, who is director of the Neuroscience & Behavior Graduate Program at the University of Nebraska at Omaha, told Discovery News.

Prior research has found that dogs and humans can also affect each other's levels of oxytocin, aka "the love hormone." There's a longstanding joke that owners and their dogs look and act like each other (think of all of the side by side photos displayed online), but there might be some truth to that notion after all.

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"Since we know that positive contact between dogs and owners results in lower cortisol levels and higher oxytocin levels in both species, it would be interesting if this effect becomes a stable, long-term trait of both the dogs and their owners," Buttner said.

She and her team did find that dogs belonging to male handlers tended to have higher cortisol levels than those with women. The researchers suspect that because men tend to be more competitive, their dogs pick up on that. The women handlers also tended to socialize with others on the agility course, which could help to decrease their cortisol levels. In any case, it's interesting that the dogs sensed all of this, with their hormones synchronizing to their humans accordingly.

The sex of the dogs didn't seem to matter, perhaps because of so many variables like spaying and neutering and the age of the canines.

The closeness between a dog and human likely enhances the hormonal synchronicity between them, although the researchers said it's possible that dogs can temporarily sync with other people too. An owner's dog might therefore briefly connect in this way with a friend or partner of the owner, and possibly even friendly strangers too.

Dogs aren't easily fooled, either. If an owner is stressed out but tries to act calm, the dog can still detect hormones in the individual's sweat that, in turn, could affect their own hormones.

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"It is also possible that they are picking up on subtle behavioral cues that you are not even aware you are emitting," Buttner said.

Now the question is: Can such closeness between people and animals--going even to the hormonal level--occur with pets other than dogs?

Duke University's Evan MacLean, who has also studied the sync between people and dogs, said, "I wouldn't be surprised."

Hormones such as oxytocin and cortisol are found in all mammals. He said oxytocin, in particular, "is probably involved in social bonds and parenting in many diverse species. If I had to bet, I'd say you'll see a paper on this with cats, or horses sooner than later."

Dogs' hormones adjust to match those of their owners, research finds.

Facial expressions among social animals appear to have universal qualities, to the point where humans and other animals can discern how certain species feel just by looking at their faces. That's the suggestion in two new studies -- published in the Journal of Veterinary Behavior and PLOS ONE -- that help explain how humans can have such close, understanding relationships with animals such as dogs and horses, the subjects of the investigations. The research confirmed, through animal behavioral analysis, the underlying meaning of dog and horse facial expressions and also demonstrated that people have a natural knack for figuring out what they mean. For example, "this dog is experiencing a positive emotional state, as his owner has just come back," Emanuela Dalla Costa told Discovery News. She led both studies and is a researcher in the Department of Veterinary Science and Public Health at the Università degli Studi di Milano. She explained that the dog’s eyes are wide open, as is his mouth, yet his facial muscles are somewhat tense. Together, these features and others suggest that he is happy, eager and hopeful.

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Here is another happy dog. In this case, Dalla Costa explained, the dog's "lips are retracted, but with no exposure of the teeth." The dog is thrilled that its owner has just returned and eagerly looks to the human for guidance.

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This poor pooch "is tense, due to the departure of his owner," Dalla Costa said. Every part of the dog's face is turned in the direction of his owner's recent exit, maximizing the pup's ability to find him. The dog's eyes and tense mouth convey his worry and loneliness.

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This dog's gaze is riveted on its owner, who is holding food. "This emotional condition is considered positive, and we can assume that this dog is happy," said Dalla Costa, adding that "there is no visible tension in the facial muscles." Even though the eyes, ears and face are pointed in one direction, just as they were for the worried and lonely dog in the previous slide, this hopeful canine feels no anxiety.

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Every aspect of this dog’s face communicates concern and worry. "The mouth is opened and the dog is panting," Dalla Costa said. "The dog’s lips are partly drawn back, with no teeth exposure. The facial muscles show some degree of tension, visible through ridges that emerge on the lateral side of the face and near the eyes." His ears are up, yet not fully open, an indication that he’s attentive but also worried.

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If this dog could talk, the canine would likely be saying, "Oh, please -- feed me." The photo was snapped as the dog looked longingly at its owner, who was holding a favorite food treat. Dalla Costa explained that there is no visible tension in the dog’s face. Its expression cleverly communicates desire and gentleness, while also revealing a sense of hopeful expectation.

Horse expressions, meanwhile, share similar qualities with dogs. This horse, similar to the dogs happily looking at their owners, is attentive and awaiting direction. "The eyes are open and focused on the environment, ears are moving in the direction of sounds, and there is no muscle tension in the mouth," said Dalla Costa.

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This unfortunate horse was photographed while in pain, which, thankfully, turned out to be only temporary. In this moment, however, Dalla Costa noted that the horse's ears are in a sideways position. Its eyes are partially closed, and its "chewing muscles are strained and prominent." Even the horse’s nostrils are stiff over its tightly shut mouth.

While perhaps not as uncomfortable as the previous horse, this horse was also photographed while experiencing temporary, minor discomfort. In this case, the horse’s nostrils are wide open, while its lower lip is drawn back. Even its "ears are held passively backward," Dalla Costa said.

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This horse is completely relaxed. "There is no tension in the mouth and in the chewing muscles," said Dalla Costa. "The nostrils are relaxed." The horse was happy to be chilling out on a pleasant day in an open field.