EN
In consequence of intensification of sheep breeding, an important question, both theoretically and practically, has become the problem of natural immunity of these animals to infectious diseases. Therefore, it seems purposeful to investigate various aspects of the defence system of organism, i.e. its immune reactivity in different physiological states and under the influence of external stimuli. One of the methods used for determination of the immunity state is in vitro examination of the immune indices to which, among other things, belong: complement, bactericidal activity of serum, phagocytosis, and antibodies. As yet, the studies dealing with natural immunity of sheep are relatively rare. No investigations on the bactericidal properties of sheep serum and influence of viral infection on the activity of defence systems of these animals, were found. The purpose of the presented investigations was to study the development of some immune parameters in sheep from birth to the 6th month of life, and the influence of pregnancy, season of the year, and infection with rabies virus on the activity of these parameters.