Summary: Researchers identify an interspecies correlation between hair cortisol concentrations in humans and dogs during summer and winter months. The cortisol levels were not affected by the amount of activity the dog had during these periods. The study reveals a seasonal effect in higher cortisol levels between humans and animals, and human personality traits significantly affected the dog’s level of stress. Findings suggest that dogs often mirror the stress levels of their owners.
Source: Linkoping University
The levels of stress in dogs and their owners follow each other, according to a new study from Linköping University, Sweden. The scientists believe that dogs mirror their owner’s stress level, rather than vice versa. The study has been published in the scientific journal Scientific Reports.
Researchers at Linköping University have examined how stress levels in dogs are influenced by lifestyle factors and by the people that the dogs live with. Previous work has shown that individuals of the same species can mirror each others’ emotional states. There is, for example, a correlation between long-term stress in children and in their mothers. The recently published study arose from scientists speculating whether similar mirroring of stress levels over long time periods can also arise between species, such as between the domesticated dog and humans. The researchers determined stress levels over several months by measuring the concentration of a stress hormone, cortisol, in a few centimetres of hair from the dog and from its owner.
“We found that the levels of long-term cortisol in the dog and its owner were synchronised, such that owners with high cortisol levels have dogs with high cortisol levels, while owners with low cortisol levels have dogs with low levels”, says Ann-Sofie Sundman of the Department of Physics, Chemistry and Biology (IFM) at LiU, principal author of the study and newly promoted doctor of ethology.
The study examined 25 border collies and 33 Shetland sheepdogs, all of them owned by women. The owners and the dogs provided hair samples on two occasions separated by a few months. Since physical activity can increase cortisol levels, the researcher also wanted to compare companion dogs with dogs that competed in obedience or agility. The physical activity levels of the dogs were therefore recorded for a week using an activity collar.
Previous research has shown that levels of short-term cortisol in saliva rise in a synchronous manner in both the dog and its owner when they compete together. The study presented here, in contrast, found that physical activity in dogs does not affect the long-term cortisol in their hair. On the other hand, the stress level of competing dogs seems to be linked more strongly with that of the owner. The scientists speculate that this may be associated with a higher degree of active interaction between the owner and the dog when they train and compete together.
The dog owners were also asked to complete two validated questionnaires related to their own and their dog’s personality. The researchers investigated whether stress levels are correlated with personality traits.
“Surprisingly enough, we found no major effect of the dog’s personality on long-term stress. The personality of the owner, on the other hand, had a strong effect. This has led us to suggest that the dog mirrors its owner’s stress”, says senior lecturer Lina Roth, also at IFM, and principal investigator for the study.
The result suggests that the match between an owner and a dog affects the dog’s stress level. Further studies are, however, needed before we can draw any conclusions about the cause of the correlation. The researchers are now planning to study other breeds. Both the border collie and the Shetland sheepdog are herding dogs, which have been bred to collaborate well with humans and respond accurately and quickly to signals. The research group is planning to investigate whether a similar synchronisation takes place between dogs and humans in, for example, hunting dogs, which have been trained to be independent. Another line of research will look at whether the sex of the owner plays a role.
“If we learn more about how different types of dog are influenced by humans, it will be possible to match dog and owner in a way that is better for both, from a stress-management point of view. It may be that certain breeds are not so deeply affected if their owner has a high stress level”, says Lina Roth.
Funding: The study has received financial support from Agria, the SKK (Swedish Kennel Club) Research Fund, and the European Research Council (ERC).
Long-term stress levels are synchronized in dogs and their owners
This study reveals, for the first time, an interspecific synchronization in long-term stress levels. Previously, acute stress, has been shown to be highly contagious both among humans and between individuals of other species. Here, long-term stress synchronization in dogs and their owners was investigated. We studied 58 dog-human dyads and analyzed their hair cortisol concentrations (HCC) at two separate occasions, reflecting levels during previous summer and winter months. The personality traits of both dogs and their owners were determined through owner-completed Dog Personality Questionnaire (DPQ) and human Big Five Inventory (BFI) surveys. In addition, the dogs’ activity levels were continuously monitored with a remote cloud-based activity collar for one week. Shetland sheepdogs (N = 33) and border collies (N = 25), balanced for sex, participated, and both pet dogs and actively competing dogs (agility and obedience) were included to represent different lifestyles. The results showed significant interspecies correlations in long-term stress where human HCC from both summer and winter samplings correlated strongly with dog HCC (summer: N = 57, χ2 = 23.697, P < 0.001, β = 0.235; winter: N = 55, χ2 = 13.796, P < 0.001, β = 0.027). Interestingly, the dogs’ activity levels did not affect HCC, nor did the amount of training sessions per week, showing that the HCC levels were not related to general physical activity. Additionally, there was a seasonal effect in HCC. However, although dogs’ personalities had little effects on their HCC, the human personality traits neuroticism, conscientiousness, and openness significantly affected dog HCC. Hence, we suggest that dogs, to a great extent, mirror the stress level of their owners.