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  Focus on animal welfare Part 1 Unpacking stress in pigs
Dr Aileen Pypers
Stress is a word that is ubiquitous in our lives. We hear about the health risks associated with stress, take holidays to unwind from stress or possibly engage in unhealthy habits to cope with stress such as eating too much, drinking too much alcohol or smoking. But what is stress and why do pig farmers need to know about stress?
What is stress?
Stress is a term that has had various meanings within the different contexts in which it has been used. For the purposes of these articles on stress, the definition proposed by Moberg will be used: “the biological response elicited when an individual perceives a threat to its homeostasis”1. There are several important concepts within this seemingly simple definition.
Stress is a biological response
The body responds by altering behaviour, activating the “fight or flight” system, secreting hormones that coordinate the stress response (namely cortisol) and up- or down- regulating the immune system, in order to ensure survival. Which of these systems, or to which extent these systems are employed is dependent on the stressor as well as the individual animal. Genetics, age, experience, social relationships and human-animal interactions
can all affect the way in which an individual responds to stress2.
Perceiving a threat can occur in different ways
Receptors inside the body communicate to the brain when blood sugar is dropping or more oxygen is needed, the various
senses take in information that the brain interprets as threats to survival either through inherent, instinctive means (e.g. spotting
a predator) or through past experience and learning, e.g. the appearance of a person in an overall results in painful handling. Therefore, whether something
is a stressor or not is in the eye
of the “perceiver” and the organ responsible for processing and interpreting all this information is the brain.
Homeostasis is a state that the body works to maintain
Resting heart rate, stable blood glucose levels, neutral or positive emotions, oxygen available to every cell that needs it – and a lot of animal and human behaviour is driven by the need to maintain homeostasis. When hungry, an

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