Environmental stress in pigs

Stress is the sum of non-specific responses of organisms to various very stimuli. The environmental factors that can cause the stress response of the body are called stressors or stress factors.

Pigs react after being stimulated by environmental factors, but the forms of response are different. General stimuli cause specific responses of the body, such as cold winter, pigs gather together, hot summer, evacuation and other phenomena. Some stimuli (stressors) not only make the body produce specific responses, but also cause non-specific reactions, that is, stress reactions, which are characterized by thickening of the adrenal cortex of ①, increased secretory activity, atrophy of thymus, spleen and other lymphoid tissues, decrease of eosinophils and lymphocytes in blood, increase of neutrophils, and bleeding of gastric and duodenal ulcers in ③. These symptoms are called systemic adaptation syndrome (GAS). So stress is not environmental stimulation, but the response of the body.

What is the significance of the animal body's response to stimuli? the previous section said that the internal environment of high-grade animals is relatively stable, and the specific responses and non-specific stress responses produced by the body are to keep the internal environment relatively stable. enhance the ability to adapt to environmental changes. Stress response is a physiological response, and its function is to mobilize all the defense systems of the body to overcome the strong stimulation that the specific response can not adapt to, so as to expand the scope of adaptation of the body and enhance its ability to adapt to the environment. If the body lacks stress response or stress disorder, it will lead to internal balance disruption (disease) or death under any stimulation that is beyond the scope of general physiological regulation (specific response). Therefore, stress is a necessary response for pig survival, which can expand the adaptive range of animals.

The occurrence and development of stress can be divided into three stages under typical circumstances.

1. Panic reaction or mobilization stage is the early response of the body to the action of stressors, resulting in GAS response. Alienation is dominant, pigs lose weight, there is a negative balance of nitrogen and carbon, and the resistance of the body is lower than the normal level. This stage is usually 48 hours, if the stress factors are very strong, pigs may die within 1 hour or 1 day; if the body overcomes the influence of stress factors and survive, then enter the adaptation stage.

two。 In the adaptation or resistance stage, the body overcomes the role of stressors and acquires adaptation, which is contrary to the mobilization stage, which shows that the metabolism of the body returns to normal, assimilation is dominant, physical condition is restored, and the resistance of the body is raised above the normal level. at the same time, the resistance to other stimuli is also improved, this stage is usually a few hours, days or weeks. If the stressor stops acting or weakens, and the body overcomes the adverse effects of stimulation, stress ends at this stage; in most cases, stress only goes through the above two stages, but if the stressor continues to act or the body cannot overcome this effect, then enter the failure stage.

3. The failure stage is very similar to the panic stage, but the degree of reaction increases sharply. Although the adrenal cortex is hypertrophic, it can not produce necessary hormones, tissue protein, fat and other body storage and decomposition, and the body weight drops sharply. The resistance gained is lost again, the adaptive function is destroyed, the system is dysfunctional, and finally the failure leads to death.

In the case of GAS in the stress process, livestock productivity, product quality, resistance and feed utilization rate are all reduced, this is because the body mobilizes the whole body defense mechanism and energy to resist the stimulation of adverse environmental factors and maintain its life activities, and production needs to consume the nutrition and energy of the body, which is disadvantageous to maintaining life, so production activities are reduced or stopped. In the adaptation stage, not only the ability of resistance is enhanced, but also the levels of physiological function and productivity are restored and compensated, thus it can be seen that stress response is a special reasonable state of physiological adaptation, only when the stress response can not overcome adverse stimuli, it leads to irreversible failure. It can be seen that for the pig itself and its survival, the stress response expands the adaptive range of the pig.

In animal husbandry production, mild stress can improve livestock resistance, productivity and feed utilization rate, but attention should be paid to control the intensity and time of stress so as to stop it in the adaptation stage and prevent the occurrence of exhaustion reaction.