Stress and immune function: a bibliographic review.

Environmental stressors are involved in the etiology of important livestock diseases, including transmissible gastroenteritis in young pigs, Newcastle's and Marek's disease in chickens and shipping fever in cattle. Unfortunately, very little research has been conducted to learn how stress alters host resistance, although it is generally assumed that the immune system of the host is affected. This paper identifies eight stressors that typically occur in modern livestock production units: heat, cold, crowding, mixing, weaning, limit-feeding, noise and restraint. All of these stressors have been shown to alter the immune system of animals. These changes in immune function may ultimately explain the physiological basis of disease-environment interactions. A thorough understanding of stress-induced changes in host resistance will also provide the scientific basis for effective prophylactic therapy. More controlled experiments are needed to learn how stress alters the susceptibility of animals to infectious and noninfectious diseases.