Stress response is the sum of the body's non-specific responses generated by a variety of very stimulations, and is the comprehensive response of hypothalamus–pituitary- adrenal cortex system. In intensive farming, varieties of stress factors include feeding factors (such as the capture, transfer group, transportation, vaccination, drug injection, forced molting, beak, etc.), environmental factors (such as heat, cold, noise, harmful gas, etc.) and pathogen infections (such as viruses, mycoplasma, bacteria, parasites, etc.). All these factors can lead to the stress response of livestock resulting the slowing down of animal growth ,decline of production performance, and the reduction of resistance to disease, which make huge losses to the livestock.
Anti-stress drugs means the drugs that can prevent and reduce stress. The excellent anti-stress drugs should have the following characteristics: significant reduction of the stress response of animals, no affection to the normal activities of animals and the formation of antibodies and no drug residues. Currently, anti-stress drugs is still at an experimental stage or clinical experience level. Anti-stress drugs are generally divided into three categories: stress preventive medicine, promoting adaptation drugs and symptomatic drugs .The stress preventive medicine can weaken the affection of stress factors to the body, such as tranquilizers, sedatives, etc; the promoting adaptation drugs can improve the body's defense force and ease and adjust the stimulation, such as methimazole, fumaric acid, vitamin C, acanthopanax,etc; the symptomatic drugs refers to the drugs fighting against stress symptoms. The above classification is relative, and a drug may can both prevent stress and promote adaptation to stress, which is not only stressed preventive medicine, but also promote adaptation drugs.