top of page

The Science of Stress: Part One

Updated: Jul 18, 2023

This is a subject which all dog guardians should familiarise themselves with because there will always be events that crop up which your dog may find stressful. It’s quite a heavy-duty topic with lots of science, but it is important to be aware of any early signs of stress in your dog so that you can minimise the effects and safeguard your dog’s physical and emotional well-being. This will also help prevent a decline into deeper stress and avoid behavioural challenges from developing. In this two-part blog, we will explore the science of stress and learn how to spot those signs!

Day-to-Day Stressors

There are many situations, objects and environments that a dog will encounter which may cause him varying degrees of stress in day-to-day life, both in the short-term and on a long-term basis. Triggers may include vehicles, fireworks, bird scarers, or any other sudden loud noises; babies crying, household appliances, children, strangers, unknown dogs, travelling in the car, or perhaps a visit to the vets. A lack of choice over whether to interact in any of these scenarios can be very worrying.

Is Stress Always a Bad Thing?

Stress is not necessarily always a negative experience; for example, it can be of use when learning something new. Your dog may experience eustress, a surge of positive stress hormones which heighten performance and boost capacity for learning. When combined with the feeling of success, some tasty treats and some playtime, this becomes a very positive outcome following short-term stress. When everything is in balance, eustress can help to build neurons and develop cognitive plasticity, leaving the dog more open to learning and better able to cope with future stressors.

Having said that short-term stress can be a very positive experience, smaller amounts of stress can also lead to a cumulative level which becomes detrimental; this usually occurs when the five freedoms are not met.

Confidence and resilience levels will vary depending on the individual, but a dog will be susceptible to feelings of stress if he is:

· Hungry or thirsty.

· Suffering from malnutrition.

· Too hot or cold.

· In pain, injured or ill.

· Isolated.

· Overwhelmed by noise or activity.

· Subjected to sudden changes to routine.

· Prevented from expressing natural behaviours.

· Feels anxious or unsafe.

Stress can occur in dogs even before they are born! Fear can be inherited, or it can develop in those as young as five weeks old, following an early negative experience; this thoroughly quashes the myth that a puppy is a blank canvas. If stress goes unnoticed and untreated, it can persist through to adulthood, as they will not simply grow out of being fearful; it can often worsen as they mature. Once they reach their normal fear impact period, it is possible that they may never pass through it.

Towards the end of the dog’s lifespan, the physical decline of his senses, such as hearing or eyesight fading, can trigger feelings of anxiety, and a loss of cognitive function can also lead to increasing levels of stress. Poor handling and training techniques with a lack of positive reinforcement can also be stressful for dogs, as well as being over or under-exercised, not being able to toilet when they need to, and not having somewhere quiet they can go to rest and sleep.

The Science Bit!

In order to discover what the internal effects of stress are, we need to understand the nervous system and the endocrine system, which are both responsible for the survival response. The nervous system is quite complex, comprising several branches and millions of nerve cells called neurons. Most of these can be found in the brain and spinal cord, which forms the central nervous system. This allows the dog to interpret and communicate, gaining information from all of their senses, whilst also controlling many internal functions.

The other main division, besides the central nervous system, is the peripheral nervous system, and is the more complex of the two. The peripheral nervous system divides into the somatic nervous system, which deals with actions under conscious control of the dog, such as movement, and the autonomic nervous system, which is responsible for the involuntary actions, such as keeping the heart beating, breathing, and digestion. It communicates sensations to the brain, such as a full bladder or upset stomach, but also reacts to environmental stimuli and perceived threats, increasing heart rate and tensing muscles while preparing for fight-or-flight.

The autonomic nervous system then branches out further into the sympathetic nervous system, the parasympathetic nervous system and the enteric, or gastrointestinal, nervous system. It is the sympathetic nervous system which handles both mental and physical activity, controlling thermoregulation, heart rate, breathing, digestion, and the fight-or-flight (fear) responses. It triggers the liver to provide glucose to the bloodstream for an energy boost and redistributes blood flow, along with increasing lung capacity by dilating the bronchioles to enable the dog to run away. It also triggers adrenaline production, it increases arterial pressure during moments of stress, and pupil dilation occurs, which is often the first sign of a change to the dog’s internal state.

When the dog no longer perceives a threat, the parasympathetic nervous system comes into play to rebalance and bring about the “rest and digest” state. It cues relaxation, stimulates digestion, slows the heart rate down and restores calmness.

Gut Health Matters!

It has been discovered more recently that there are millions of neurons in the intestines which form the enteric nervous system, meaning that there is a direct link between the dog’s emotions and his gut. What he eats will directly affect his behaviour and impact on his emotions, and every emotion and response will affect the body. The hypothalamus, part of the limbic system and emotional centre of the dog, controls the release of pituitary hormones and regulates behavioural responses alongside basic life functions, and is tied in to the autonomic nervous system. The direct link between the limbic system and autonomic nervous system means that emotions have physical consequences and will affect behaviour. The amygdala, also part of the limbic system, is responsible for survival and defence. Danger or perceived threat messages are sent directly to the amygdala and bypass the thinking area of the brain. Fear increases, as does aggression, and the dog reacts increasingly because his body is flooded by hormones. Fear aggression is a symptom of the sympathetic nervous system’s actions, and once the dog is over threshold, thinking is affected and learning cannot occur.

The endocrine system works alongside the nervous system and handles hormone production through glands and organs found throughout the body. Hormones are chemicals designed to regulate, coordinate, and control basic bodily functions. The endocrine system includes the hypothalamus, the pituitary and thyroid gland, parathyroid glands, adrenal glands, parts of the gastrointestinal tract, pancreas, kidneys, liver, ovaries and testes. Input from the nervous system can trigger the endocrine system to produce hormones, including cortisol, adrenaline, testosterone and vasopressin. Hormone levels are controlled by feedback loops in the endocrine system, and the body is able to trigger the producing gland to shut off when a hormone is detected at a certain level. However, when a physical abnormality is present, glands may over or under-produce the necessary hormones and the feedback loops may not always be effective, leading to chemical imbalances, which have clear and important physical signs.

The Fight or Flight Response

Part of the survival mechanism of the fight-or-flight response is the reflex arc, where the body reacts to sudden pain via the spinal cord, without waiting for input from the brain. The sensation causes two signals to be sent simultaneously, one to the affected area so that the muscles can activate and move away from the source of the pain, and the second to the brain, in order to register the risk or thing which caused it. Pain also causes an increase in the stress hormones, and adrenaline is known to have pain-relieving properties, which can mask pain. An example of this occurrence is when you might take your dog to the vet with a suspected injury, but he shows no obvious signs of pain when examined, leaving you feeling rather sheepish and confused, while your dog still isn’t quite right.

When a dog encounters something stressful, there is an internal reaction which leads to several changes within the body, and an external display is present. When he begins to feel distressed, the sympathetic division of the nervous system comes into play and the fight-or-flight mechanism is triggered, which affects the immune system, the digestive system, and his hormones. The nervous system and endocrine system take action through electrical impulses and hormones, which are released into the bloodstream to keep him alive, beginning with an influx of adrenaline and cortisol to enable him to either take flight or fight. Glucocorticoids are released from the adrenal cortex, and the adrenaline and cortisol create a negative feedback loop, which then activates the immune system. Blood pressure and pulse increase, whilst digestion becomes no longer important. There is a flood of glucose from the liver to provide extra energy, and the immune system shuts down so that energy is prioritised for the survival functions.

The dog’s response, whether that is flight, fight, fool around, faint or freeze, will depend on the environment, and how the dog has learned to cope when faced with a perceived threat. The first choice would usually be to take flight if he can, with fight normally being a last resort. The initial release of adrenaline may clear from his body within fifteen minutes, but the glucocorticoids released in a secondary phase can take forty-eight hours to six days to subside, and it can take four to six weeks of avoiding triggers to allow the dog to return to a baseline state.

There are many physical signs of stress that dogs may display when under pressure and feeling stressed, some temporary and others longer-lasting. An excess of testosterone and vasopressin has a direct link to aggression, whereas dogs with higher levels of oxytocin tend to be friendlier and less aggressive. Dogs can become noise-phobic, suffer from Separation Anxiety and develop fearful and reactive behaviours; these issues all have a prolonged and exaggerated stress reaction, with serious mental and physical consequences.

The stress response is necessary for survival and normal stress is only short-term and appropriate in relation to the trigger, but if a dog is regularly exposed to multiple triggers, he will suffer physically, psychologically and emotionally and it will lead to lower immunity, poor digestion, poor recuperation from injury and he will be more prone to illness and infection. Longer term stress causes digestion to become compromised, because fewer nutrients are delivered to the cells, and less nutrition means a lower functioning capacity. Stressed dogs feel anxious and are not concerned with eating. When they eat, they are likely to eat quickly, which means that food won’t be properly processed, as blood flow is diverted and digestion decreases. They may also not eliminate properly, which can lead to a build-up of toxins. The endocrine system suffers, which causes a hormonal imbalance, leading to poor behaviour. High levels of cortisol remaining in the body can also lead to shedding of the coat, and skin issues such as dandruff may occur.

With a single exposure to a trigger being experienced by the dog, the effects of the stress reaction can remain for up to seventy-two hours, so repeated exposure can understandably lead to long-term damage if the dog cannot return to a state of relaxation. If a dog suffers from chronic stress, this can also lead to kidney problems and heart issues. Glucocorticoids sap the immune system and if any medication is administered, this becomes a further toxin and can compromise other bodily systems. Therefore, it is vital to minimise exposure to triggers as much as possible and keep the dog feeling safe so that he can recover both physically and mentally in order to avoid a decline towards chronic stress. You can read more about how to keep your dog feeling safe here:

Join me in part two to discover how to spot the earliest signs of stress, helping to keep your dog’s physical and emotional health in tip-top condition!

If you have found this useful, why not subscribe to receive my future blog posts? Don’t forget to check your junk mail folder, just in case! You can also find my blogs, along with other science-based, dog-centred posts and articles over on my Facebook page: Trailie Paws For Thought | Facebook

551 views0 comments


Post: Blog2_Post
bottom of page