Novelty of the research: 1. During the experiments was defined composition of the anaerobic microflora in the rumen fluid of dairy cows and carried out its comparative evaluation when cows were fed the rations of different composition and nutritional value and different feeding technologies were applied. 2. The effect of biochemical parameters in the rumen fluid of dairy cows on their bacterial count and composition was also studied. 3. During the experiments great attention was paid to the dependence of various forages organic matter digestibility in vitro on the amount and composition of the anaerobic microflora in the rumen fluid of dairy cows. 4. The comparative evaluation of different forages digestibility in vitro was carried out in variable microbiological and biochemical conditions of the rumen fluid. Practical importance: 1. At the Research Center of Digestive Physiology and Pathology, Department of Anatomy and Physiology of LVA was implemented method for the cultivation of rumen obligative anaerobes cultivation. 2. Biochemical and microbiological parameters of the rumen fluid of dairy cows, composition of anaerobic microflora, its effect on the activity of fermentative processes when dairy cows are fed rations of different composition and nutritional value, applying different feeding technologies were studied.