Washington D.C. [USA], Sep 28 : A team of researchers has recently found discovered two hormones, which cause some dogs to become aggressive on the leash, while others are able to maintain their typically friendly disposition.
According to researchers from the University Of Arizona in Tucson U.S. oxytocin and vasopressin -- hormones that are also found in humans -- may play an important role in shaping dogs' social behaviour.
"Dog aggression is a huge problem. Thousands of people are hospitalised every year for dog bites, especially kids, and aggression is one of the main reasons that dogs get relinquished to shelters," said lead researcher Evan MacLean.
"If there are ways to intervene and affect biological processes that produce aggression then that could have a huge benefit on both for people and dogs," Maclean stated.
The team was interested in oxytocin and vasopressin -- sometimes thought of as "yin and yang" hormones -- because of the growing research on their role in the biology of social behaviour.
Oxytocin, which is significant in childbirth and nursing, is sometimes called the "love hormone," as its level in humans has been shown to increase when we hug or kiss a loved one.
Vasopressin is a closely related hormone involved in water retention in the body.
In contrast to oxytocin, it has been linked to aggression in humans, with previous research suggesting that people with chronic aggression problems have high levels of vasopressin.
The team recruited pet dogs of varying ages, breeds and sexes, whose owners reported struggles with leash aggression.
For each aggressive dog recruited, they found a non-aggressive dog of the same sex, age and breed to serve as a comparison.
During the experiment, each dog was held on a leash by its owner.
Across the room, an experimenter played audio of a dog barking behind a curtain, before pulling back the curtain to reveal a lifelike dog model with a human handler.
The dogs' responses and hormone levels were measured before and after the interaction.
The dogs that reacted aggressively showed higher levels of total vasopressin in their systems, suggesting a link between vasopressin and aggression.
The researchers did not observe differences in oxytocin levels between the two groups of dogs.
They found that the assistance dogs had higher levels of oxytocin and higher oxytocin-to-vasopressin ratios. This supports the idea that oxytocin may help inhibit aggression in dogs.
"Seeing high oxytocin levels in assistance dogs is completely consistent with their behavioural phenotype -- that they're very, very friendly dogs that are not aggressive toward people or other dogs," MacLean noted.
The research appears in the journal Frontiers in Psychology.