TY JOUR TI NATURAL BIOLOGICALLY ACTIVE PREPARATION FOR FEEDING CALVES KW calves KW biologically active product KW digestibility coefficients KW calf blood biochemistry KW absolute weight gain in calves KW feed conversion ratio for calves JO Bulletin of KSAU AU Lashkova, T.B. AU Petrova, G.V. AU Zhukova, M.Y. PY 2026 IS 0 PB Krasnoyarsk State Agrarian University