A short-term stress response to a specific event or stimulus, characterised by activation of the sympathetic nervous system and a brief spike in cortisol.

A horse showing acute stress at the start of an unfamiliar journey, a dog showing acute stress at the start of a vet visit, a cat showing acute stress when meeting a new household member, are all showing healthy nervous systems responding to challenge. The acute stress response is evolved, conserved across mammals, and serves an important function: it mobilises the body’s resources to handle the challenge at hand.

Acute stress is not in itself a welfare problem. It is part of normal life and an inability to mount an acute stress response would be much more concerning than the response itself. The welfare concern arises in two specific circumstances. First, when acute stress becomes chronic stress through repeated activation that does not have time to resolve. Second, when acute stress responses are repeatedly elicited at levels that exceed the animal’s capacity to cope, which can produce learned helplessness or sensitisation over time.

The physiology of acute stress is well-characterised. The sympathetic nervous system activates within seconds, raising heart rate, redirecting blood flow, releasing adrenaline. The HPA axis (hypothalamic-pituitary-adrenal) activates over minutes, releasing cortisol that mobilises energy and modulates immune function. These responses are time-limited; in a normal acute stress event, the animal’s physiology returns to baseline within minutes to hours of the stressor ending.

Welfare assessment in research and clinical practice distinguishes between acute stress (typically tolerable when not excessive) and chronic stress (typically a welfare problem). Some level of acute stress in an animal’s life is unavoidable and probably contributes to normal nervous system development; the goal of welfare-positive management is not to eliminate acute stress but to ensure recovery between stressors.