Stress and its impact on animal welfare

Abstract

Stress is the response that is triggered in the organism in the presence of stimuli that individuals detect as dangerous and that puts their physical and emotional integrity at risk, causing changes in homeostasis and alteration of the normal physiology of animals. This stimulus can be external (for example, a prey fleeing from its predator) or internal (presence of hunger or thirst). Hans Selye was the first to discover that animals underwent these stress episodes in response to certain stimuli, and that the response followed the same pattern, regardless of which stimulus triggered the response. Lennart Levi continued the research on stress and how it affected different animals and gave a name to what we know as eustress (positive stress) and distress (negative stress). Two equally important systems are involved in the stress response: the central nervous system and the endocrine system. The central nervous system is responsible for sending signals to the sympathetic and parasympathetic nervous system, leading to the elaboration of the rapid stress response, which involves an increase in catecholamines. On the other hand, the endocrine system is in charge of activating the long-term response, through the hypothalamus-pituitary-gonadal complex, in charge of stimulating the increase of cortisol in the blood, altering all the physiological mechanisms of the organism and adapting them to the stress situation. A relationship between stress and certain diseases has been observed, although some of them are still hypothetical research cases. An example of this is feline idiopathic cystitis, whose main reason is the increase of stress peaks in cats, which causes alterations of the lower urinary tract causing dysuria, hematuria and stranguria. It is also related to cardiac pathologies such as myxomatous valvular degeneration and arterial hypertension due to the presence of chronic stress. On the other hand, certain diseases generate alterations in the normal stress response, as is the case of hypoadrenocorticism, an endocrine pathology that causes a decrease in cortisol levels in the blood, generating homeostatic alterations, and whose treatment consists in the application of exogenous corticoid. Finally, we relate the influence that stress has on puppies and their future behavior, and how stressful stimuli in certain stages of their development are necessary, as long as this stimulus is not intense or chronified in time, since it could entail future behavioral consequences with the presence of aggressiveness or fear, among others.