The purpose of the research was to determine the effect of feed nutrients, in particular, silage prepared from a wheat-oat mixture with the use of the probiotic preparation kt-l 18/1 (selection of the probiotics laboratory of the institute of agricultural microbiology and apv) in a dose of 8.0 ml of suspension per 1 ton of green mass on the fractional composition of milk proteins and its qualityand on the productivity of cows in the forest-steppe zone of the Carpathian region.
 The research was carried out on two groups of lactating cows of the Ukrainian black-spotted breed, similar in age, live weight and milk yield for the previous lactation, 10 cows each. In each the animals of both groups received the basic diet, in addition to which the cows of the control group were fed 20 kg of wheat-oat silage prepared on the farm according to traditional technology, and the experimental group - 19 kg of silage preserved with the use of the probiotic KT-l 18/1.
 It was established that the use of probiotics for harvesting silage contributed to obtaining a high-quality product, the introduction of which into the rations of cows in the transition period made it possible to minimize the deficit of dry matter (from 19.8 to 9.1%) and protein (from 4.2% to2.1%), and in winter – from 28.0 to 8.5% in terms of dry matter and from 10.1 to 0% in terms of protein, respectively.
 The study of the chemical composition showed an increase in the content of dry matter, mainly due to the total protein, fat and casein in the milk of experimental cows both in the transitional and stable periods of retention
 The milk of the cows of the research group during the stable period of storage contained more dry matter, fat, total protein and casein, respectively, by 4.8; 3,4; 5.2 and 5.6% than the control, which led to an increase in its density by 0.7 оА.
 In the milk of experimental cows, the improvement of parameters affecting its syrupiness was noted: casein content, density. According to both the reductase test and the fermentation test, which indicates the presence of gas-forming microflora in the milk and its syrupy quality, the milk of the control cows was assigned to the ІІ, and the experimental cows to the І quality class.
 The average daily yield of natural milk for 45 days of the accounting period in the experimental group was 16.7 kg and was 5.7% higher than in the control group (15.8 kg).