EN
The gastrointestinal tract of animals harbors a large, complex and dynamic microbiome important to the growth and health of livestock animals. This microbiome can be directly modulated, for example by antibiotic treatment or by various bioactive substances. Following the ban on the in-feed use of antibiotic growth promoters in the EU, an increased effort has been put into discovering an alternative in animal production. An indispensable tool for the evaluation of bioactive substances are complex studies combining in vitro and in vivo methods. They consist of precision tests that make it possible to evaluate not only the characteristics of specific strains of bacteria, but also the safety of their application. This paper presents the most important methods for the evaluation and selection of in vitro and in vivo bioactive substances that make it possible to stimulate the gastrointestinal microbiome of animals.