The problem of pneumoenteritis of young cattle with a viral-bacterial etiology remains urgent and serious, despite the impressive arsenal of means to combat these diseases. At the moment, many different drugs have been created and are being used to treat and prevent pneumoenteritis in calves based on antibiotics, sulfanilamides, nitrofurans and their combinations. Their significant disadvantage is the reduction of their therapeutic effectiveness due to the emergence of resistant strains of microorganisms, the absence of antifungal action and their unsafe environmental situation. Their replacement belongs to probiotics, which find widespread use in the treatment of sick animals with impaired gut microbiocenosis, respiratory tract, as well as correction of microbiocenosis after the use of antibiotics. The purpose of the present studies is to study a comparative assessment of the biological activity of the probiotic preparation "BIFILIZ - N" using diffusion and spectrophotometric methods. It has been found that diffusion and spectrophotometric methods for evaluating antagonistic or biological microorganisms with test cultures are recommended to be used to evaluate the quality of the preparation.