The acute and chronic stress response

In evolutionary terms, the acute, or immediate, stress response places a dog into a state of biological preparedness. This optimises the physical ability of the dog to respond appropriately to the challenge, with the aim of surviving long enough to reproduce and pass on genetic material.

This might be achieved through avoidance or repulsion of the stressor as we discuss in our section on canine behaviour.

The acute stress response increases arousal to prepare the dog for potential action. This involves activity within the sympathetic nervous system such as:  

• elevated adrenaline (epinephrine) and noradrenaline (norepinephrine) released from the adrenal medulla 
• increased blood glucose – due to increased glucocorticoid release from the cortex of the adrenal gland which promotes gluconeogenesis (formation of glucose) and antagonises insulin production, which helps to provide energy in anticipation of required action-taking 
• potential for immune suppression in response to elevated glucocorticoid levels  
• potential emptying of the bladder and bowel might also occur as part of the individual’s physiological preparedness to attend to perceived danger 

Stressors will be relative to the individual, for example, some dogs might be more sensitive to auditory rather than visual stimuli.

However, potentially triggering stimuli might have a greater impact if combined – as is likely within the veterinary clinic – and particularly where a dog might have learned, through repeated previous exposure to these contextual stressors, to anticipate negative outcomes here.

Repeated exposure to a stressor

Repeated exposure to a stimulus with the potential to trigger a stress response might affect the individual in one of two ways:

Habituation 

This is a decrease in the behavioural response to a stimulus through repeated exposure. Here, the stimulus is perceived as neutral, neither threatening nor positively exciting, and exposure results in no change in arousal.

If a dog becomes habituated to a stimulus it is unlikely to trigger any physiological response and change in behaviour. 

Sensitisation

This is an amplification of the physiological and emotional response to a stimulus through repeated exposure. Here, exposure elevates arousal.

Once a dog becomes sensitised to a stimulus, exposure to it is likely to trigger an involuntary physiological and behavioural response.   

Sensitised dogs may appear to be in a state of heightened arousal in which additional stressors, previously experienced as mild or low-level, might now elicit a physiological response of greater intensity or of extended duration.

This is often accompanied by hypervigilance, for example, a dog actively scanning the waiting room, unable to settle, with an increased propensity to startle.   

Coping with stressors

The intensity and duration of a stressor can also impact a dog’s ability to cope with its presence.

For example, a dog might be able to tolerate coming into the veterinary clinic waiting area for a ‘visit’ to collect a repeat prescription, but might be unable to continue to cope when taken into the consultation room for a clinical examination and held for a blood test this is known as situation stacking. 

Through associative learning, dogs can become so classically conditioned to stressors that their lowest-level presence and even the anticipation that they might present (triggered by environmental contextual cues) will elicit anxiety and distress.  

In general, most individuals are less anxious and better able to cope if they have one or both of the certainties below. 

• predictability: this allows an individual to prepare to deal with a recognised stressor. 
• control: an individual who has a means of controlling their own exposure to a stressor can take steps to reduce its impact.
  
  For example, a dog who is frightened of unfamiliar visitors to the home might choose to hide within a designated safe den (as long as it is provided for them) as a means of controlling their own environment in order to feel safer.