Dogs cry when reunited with owners, study shows

A new study by Japanese scientists suggests that a dog’s eyes may fill with tears of happiness when it reunites with its owner after a period of absence. Tears can help strengthen the bond between humans and dogs, a relationship that goes back tens of thousands of years.

Like humans, dogs have tear ducts that fill with tears to keep their eyes clear and healthy. But tears in dogs, which usually do not flow, as when people cry, was not previously associated with emotions.

Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, decided to study dog ​​tears after observing one of his two standard poodles when she had puppies six years ago. He noticed that her eyes filled with tears as she fed her puppies.

“We found that dogs’ tears are associated with positive emotions,” said Kikusui, co-author of the study, published Monday in Journal of Current Biology, with news releases.

“We also discovered oxytocin as a possible underlying mechanism,” Kikusui said, referring to a hormone sometimes referred to in humans as the love hormone or maternal hormone.

To investigate this link, Kikusui and his team measured the amount of tears in 18 dogs using a standard test known as the Schirmer tear test. it used a paper strip placed inside the dog’s eyelids for a minute before and after they were reunited with their owners after five to seven hours of separation.

“Tear volume was assessed by the length of the wet part on STT. The baseline was about 22mm and the owner reunion increased by 10%,” Kikusui explained via email.

Then, using 20 dogs, the researchers compared the number of tears before and after being reunited with their owners and people with whom the animals were familiar. Only the reunion with the owner increased the number of tears.

To understand whether oxytocin plays a role in tear production, a solution containing the hormone was applied to the surface of the eyes of 22 dogs. The number of tears increased significantly after the application of oxytocin compared with the control solution.

Researchers still don’t know much about dog tears. People often cry in response to negative emotions, but the researchers haven’t tested whether dogs do the same. They also don’t know if a dog’s ability to cry plays a social function in dogs. World.

Kikusui said maybe people would take better care of dogs that have watery eyes. His team showed 74 people images of dog faces with and without artificial tears and asked to rank the animals. People gave more positive responses when they saw dogs with tears in their eyes.

“Dogs have become partners with people,” Kikusui said in a statement, “and we can form bonds.”

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