Dog Depression! Is Play the Medicine Your Dog Needs?

Is dog depression real? Max seemed to be having a bad time over the past couple of weeks. He had lost his appetite, was not eating or drinking the way he normally did and thus, was losing weight quickly. He seemed to be lethargic, and spent a lot more time than usual sleeping. When he was awake, he seemed nervous, edgy, and common events seemed to worry him. None of the usual activities that normally made him happy seemed to interest him. Any psychologist seeing a person with Max’s symptoms would conclude that he was probably suffering from stress and its most common companion ailment, depression. The problem is that Max is not a person, but a German Shepherd.

It was the late 1980s when Nicholas Dodman of the School of Veterinary Medicine at Tufts University was standing next to a colleague looking at a dog that had been brought into the Animal Behavior Clinic. The dog was showing symptoms similar to Max. Extrapolating from what he knew about human behavioural symptoms, Dr. Dodman concluded that the dog he was examining that day was stressed and depressed. For a human with these symptoms, the diagnosis would have been clinical depression, and so it seemed to him that this was also a reasonable diagnosis to suggest for the dog. His colleague shook his head and warned him about the dangers of treating dogs as if they had such human-like feelings. His colleague argued, “Dogs don’t experience the same mental states and emotions that people do.”

Dr. Dodman responded, “Look, the dog's brain is structurally similar to that of a human being. The biochemistry of a dog's nervous system works exactly the same as it does in humans. We now know stress and depression in humans is accompanied by chemical and hormonal changes. Here we have a dog who is showing the same kinds of symptoms, which we might observe in a stressed and depressed person. Let me propose an experimental treatment. Let’s give the dog an antidepressant drug, the same kind that we use in people, and see what happens.” 

What happened made history since the dog’s behaviour improved dramatically and ever since then veterinarians and animal behaviorists have begun to accept the fact that dogs, like people, can suffer from the psychological and physical 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). It is the long term stressors which are the most dangerous since psychological research has shown that these can cause a variety of physical and mental problems. Thus, people under continuing stress are more likely to have cardiovascular and immune system difficulties, and also are most apt to suffer from depression and other psychological troubles. The same holds for dogs, and to counteract the effects of continuing stress and depression, veterinarians now often follow Dodman's υ lead and prescribe the canine equivalent of Prozac. Such treatment has become so common for dogs that this canine antidepressant drug now even comes in beef flavour.

When behavioural 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 researchers had to rely on visible signs and signals from the dog. These were the ones that Dodman was using and also include a variety of signs specifically based upon canine body language, such as observation on how the dog's ears are postured and the activity of the dog’s tail. While such signals can answer the yes or no question, “Is this dog stressed?”, it cannot provide a quantitative measure of just how stressed the dog is.

The breakthrough for the study of canine stress came when researchers recognized that stressed dogs secrete the same anxiety related hormones 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. For researchers, the concentration of cortisol is a wonderful tool since it is possible to determine, in real time, the amount of stress 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 in the way that drawing blood might).

However, suppose a researcher was interested in measuring the continuing stress levels experienced by a 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 labour-intensive process, but the radioimmunoassay to determine the cortisol concentration in each sample is complex and costly.

“Significantly lower cortisol levels, indicating lower long-term stress levels, were found in the dogs whose owners played with them often.”

Fortunately, a new technique has been developed. It turns out that molecules 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 surmise 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 dog owners filled out several different research questionnaires, which were designed to give information about the personality of the dogs, their typical behaviours, and the lifestyle the dogs most commonly experienced.

As might be expected with so many measures, a large number of results were reported, some showing complex and difficult to interpret findings. However, the most impressive finding was a pattern of results, which showed dogs who experience positive human interactions are much less likely to experience chronic stress responses extending over time.

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 simply 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 part of the dog, such activity alone might have bumped up cortisol responses. However, this data shows playful interactions between the dog and the owner serve as a prolonged buffer against stress in canines.

Finally, confirming many earlier reports, which showed 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 chance to play with a toy when the dog behaves correctly.

The researchers summarize their results saying, “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 a reduction in a dog's sustained stress levels can be obtained simply from common short episodes involving positive interactions. Who would have thought that by simply tossing a tennis ball for your dog to fetch or playing tug-of-war, you are effectively providing your dog with a stress reducing antidepressant effect that seems to last over a substantial amount of time. And all of this is confirmed by the long-term diary of a dog's day-to-day stress levels, as recorded in his fur!