The influence of weather conditions in the autumn-winter period and in the growing season on the content of crude protein, crude fiber and crude fat in the dry matter of alfalfa (Medicago varia Mart.) in the flowering phase has been studied. It was found that if during the formation of alfalfa herbage weather conditions were such to the average annual, the content of crude protein was 17.1–20.6%, crude fiber 24.5–28.6% and crude fat 2.4–3.3 percent. In conditions of sufficient moisture supply, increased heat supply and the predominance of Sunny days, the protein content reached to 18.9–24.8%, fiber was 19.0–23.0%, fat was 1.7–2.4 percent. With high heat and moisture with a predominance of cloudy weather, the protein content decreased to 15.0–17.7%, fiber increased to 35.4–39.3%, fat – to 2.6–3.5 percent. It was found that excessively wet weather in the autumn-winter period of the previous year significantly weakens alfalfa plants. Therefore, the beginning of spring regrowth, even in warm weather in April, was delayed for
1–2 weeks. The intensity of growth and development of alfalfa in May–June, even with optimal heat and moisture, was slow. The entry of alfalfa into the flowering phase was late by an average of 2 weeks compared to normal dates. At the same time, the content of crude protein decreases to 12.4–15.0%, the content of crude fiber increases to 32.1–34.4%, and the content of crude fat (2.4–2.9%) was not affected by unfavorable wintering conditions. It was found that the relatively high quality of dry matter in the flowering phase (average for 4 years of use) have varieties Vega 87 and Taisia (protein content of 18.3 and 19.5%, fiber 29.3 and 29.2%, fat 2.7 and 3.0%). Performance of alfalfa varieties to Pastbishchnaya 88 and Selena was a 15.9%, 30.9%, 2.3% and 17.3%, 28.8 %, 2.7%, respectively.