Playing with Your Dog Can Reduce Its Long-term Stress Level
Positive interactions reduce enduring blood stress hormone levels in dogs.
Posted May 8, 2019
Dogs, like people, can suffer from the effects of stress. Stressors come in a variety of different types, but one of the most important factors is how long the stress continues. Some stressors can be severe but short in duration, like when you safely survive a traffic accident, while others can be long-term, such as continuing financial difficulties. The long-time stressors are most dangerous since psychological research has shown that these can cause a variety of physical and mental problems. People under continuing stress are more likely to have cardiovascular and immune system difficulties and also are apt to suffer from depression and other psychological maladies. The same holds for dogs, and to counteract the effects of continuing stress and depression veterinarians often prescribe a canine equivalent of Prozac (beef flavored, of course).
When behavioral researchers became interested in the study of stress in dogs they encountered some problems. Dogs are not verbal, so they can't tell us when they are feeling tense and anxious. That meant that researchers had to rely on visible signs and signals from the dog. These included a variety of signs based upon body language, such as how the dog's ears were postured, the activity of the dog's tail, whether the dog crouched or cowered or moved lethargically, and so forth. While such signals can answer the yes-or-no question, "Is this dog stressed?" it cannot give you a quantitative measure of just how stressed is the dog is.
The breakthrough for the study of canine stress came when researchers recognized that dogs that are under stress secrete the same hormones that humans do. The critical marker for stress is the amount of cortisol that is released into the blood system, since this plays a crucial part in the body's response to different kinds of stressors. In dogs, for example, an increased cortisol level can indicate a sharp increase in stress from a sudden frightening stimulus or other worrisome events. For researchers the concentration of cortisol is a wonderful tool since it is possible to determine, in real time, the amount of stress that the dog is feeling by taking blood samples, or more recently, by simply taking saliva samples—which is better since swabbing the dog's mouth does not add to his stress level the way that drawing blood might.
However, suppose that the researcher was interested in measuring the continuing stress level experienced by the dog over a period of days, weeks, or longer. This would require many saliva swabs to be taken over a long period of time, perhaps on a daily schedule. Not only is this a labor-intensive process, but the radioimmunoassay to determine the cortisol concentration in each sample is complex and costly.
Fortunately, a new technique has been developed. It turns out that bits of cortisol in the blood also tend to be incorporated into growing hair (or fur). As the hair grows one begins to get an extended picture of the amount of cortisol in the body, and presumably the amount of stress experienced by the individual over longer periods of time. Studies on humans have shown increased cortisol levels in hair of individuals suffering from chronic pain, people who are unemployed, and those who have continuing depression. Based on such findings one can guess that dogs living with long-term stress levels will show greater amounts of cortisol in their fur.
This was the underlying hypothesis adopted by a team of researchers headed by Lina Roth at the biology department at Linköping University in Sweden. Theirs was an extended study with lots of different measures. The test subjects were 59 German shepherds. (The investigators chose to limit their testing to one breed in order to reduce the likelihood of any possible genetic differences.) The dogs were tested three times, in January, May, and September of the same year. At these times, fur samples were taken and analyzed for their cortisol level. In addition, the dogs' owners filled out several different questionnaires designed to provide information about the dogs' personalities, their typical behaviors, and the lifestyle that they most commonly experienced.
As might be expected, a large number of results were reported, some showing some complex and difficult-to-interpret patterns. However, what impressed me was a cluster of results which showed that dogs who experience positive human interactions are much less likely to experience chronic stress responses over time, as confirmed by the level of cortisol in their fur.
Setting the tone for this was the fact that lower cortisol levels were found in the dogs owned by people who agreed with the statement that the purpose of the dog is to have a nice companion.
Significantly lower cortisol levels, indicating lower long-term stress levels, were found in the dogs whose owners played with them often. One might have expected that since most play activities involve lots of movement on the dog's part, that activity alone might have bumped up cortisol responses. However, these data show that playful interactions between the dog and the owner serve as a prolonged buffer against stress in canines.
Finally, confirming many earlier reports which showed that the use of rewards during training has a more beneficial effect on dogs than the application of force or discipline, this study found lower cortisol levels for dogs whose owners report that they usually reward the dog with a treat or a toy when the dog behaves correctly.
The researchers summarize their results as follows:
"Maybe not surprising but [a] still welcome result is that a negative correlation was found between cortisol level and how often the owner played with their dog and also whether the owners used [a] toy/treat when rewarding their dog. Both these results could reflect that friendly and encouraging relationships are related to less stress in the dogs."
The good news from this study is that the reduction in stress from these positive interactions seems to last over a substantial amount of time.
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Roth LSV, Faresjö Å, Theodorsson E, & Jensen P (2016) Hair cortisol varies with season and lifestyle and relates to human interactions in German shepherd dogs. Scientific Reports 6:19631.