The Effects of Stress on Animals

It's ironic that I'm about to talk to you about the effects of stress on animals because I currently look like this:

On a more serious note.. stress can be a very important measure of animal welfare. Stress can potentially show that there is a problem with the animal's welfare, particularly in captive environments. For example in a zoo with a monorail going over an enclosure, if an animal becomes stressed every time the monorail goes over it can indicate that the monorail is having a significant detrimental effect on their welfare.Stress is an important process as it allows the body to adapt to change. The stress response is triggered by a threat such as a decrease in temperature. This causes the hypothalamus in the brain to release corticotropin-releasing hormone (CRF) which travels to the anterior pituitary. CRF controls the release of adrenocorticotropic hormone which stimulates the adrenal cortex to secrete cortisol.

Cortisol is responsible for the body's response to stress. The cells which are not needed for what we call the "fight or flight" response are stimulated by cortisol so that they decrease their use of blood glucose and start using fats and proteins for energy instead. Processes such as immune system reactions are also turned off as they are not needed to cope with the stress. Metabolic rate is therefore increased and life-sustaining processes have more energy. Cortisol is a type of Corticosteroid which are used in stressful circumstances. Corticosteroids stimulate glucose production from fat (as mentioned above), break down the tissue protein, increase the sensitivity of the blood vessels to adrenaline (to allow fight or flight), increase the rate of urine formation, make muscles function for longer, affect brain excitability, increase gastric acid and pepsin secretion, act as an anti-inflammatory and suppress the immune system (as mentioned above). Once the stress response has served its purpose cortisol effects the cells of the brain which causes a decrease in the release of CRF in a negative feedback loop.

The effect of stress on the body has three different stages depending on the length of time the stress is present. The first stage is called the Alarm Stage. This is when the body first reacts to the stress and it's response is in a state of alarm. At this point adrenaline is produced so that the fight or flight response can be used. There is also some activation of the HPA axis, producing cortisol. If the stressor persists then the body begins to adapt to the change and this is called the Adaptation Stage. However, if the stressor persists for too long then the body enters the Exhaustion Stage and it's resources become depleted. This can cause long term damage to the individual with effects such as ulcers, depression, diabetes or cardiovascular problems and it must therefore be avoided at all costs.

The physiological processes which occur when an organism is stressed allow us to measure welfare effectively by taking measurements of cortisol or other corticosteroids. This allows for improvements to be made to a captive animals environment using enrichment. It can also be combined with behavioural welfare assessments to get a better result.