Methods of modern control of infectious animal diseases have led to a change in the etiological structure of infectious agents. Irrational use of antibiotic therapy may be the cause of bacterial variability and involvement in the infectious process of opportunistic bacteria that are present in the normal microflora of the animal body. Opportunistic bacteria are the cause of many animal diseases. Infections caused by them have a prolonged character, the pathogenetic basis of which is the persistence of the pathogen in the host body. Bacterial exotoxins damage the plasma membrane of cells. Pore-forming toxins and enzymes disrupt the selective entry and exit of ions through the plasma membrane. This group of toxins includes cytolysins, hemolysins of gram-negative opportunistic enterobacteria, leukotoxins, metalloproteases, and lipases. When pores are formed under the action of hemolysin, secondary processes are triggered that cause the development of pathological consequences. The vaccines and serums produced by biofactories lag behind the practical needs in terms of antigenicity and do not provide protection for newborn calves in the system of anti-epizootic measures. Of particular importance in the etiopathogenesis of acute intestinal disorders is a decrease in colonization resistance of the gastrointestinal mucosa, resulting in an expansion of the spectrum of pathogenic and opportunistic microorganisms that lead to the development of diarrhea.

The study of stress sensitivity in newborn animals is an urgent problem. According to the type of neurohumoral activity, animals differ from each other. The body’s response to the effects of stress can manifest itself in the form of adaptation or exhaustion. One of the most recognized definitions of the term “disease” is damage to the structure and function of the body under the influence of external factors during the reactive mobilization of its compensatory and adaptive mechanisms. As well as a set of non-specific changes in the body that are the result of its neurohumoral response to external stimuli that are stress. Based on the above, we set the following tasks: to develop a method for detecting stress-dependent animals; to study the effect of stress on the immune system of newborn calves; to study the influence of the Central nervous system on the manifestation of regrouping stress and its correction using sedatives. Experiments to study stress sensitivity were performed on newborn calves. A method was developed for detecting stress sensitivity in newborn calves, according to the formulated formula (know-how). Animals that have u.e according to the formula below 1.35 refers to stress-resistant, and with a value above 1.35-to stress-sensitive. When studying the effect of stress on the immune system, differences in indicators were found depending on stress sensitivity.