TELISHEVSKAYA, A.A. SARKHANOVA, L.V. VASIL’EVA, E.G. TITOVA, A.N. PANIN Federal Agency of Scientific Organizations, 5, Zvenigorodskoe sh., Moscow, 123022 Russia, e-mail l.telishi@mail.ru Abstract Worldwide a large number of enzymes, including those with endo-β-glucanase activity are produced by different companies as fodder additives. <...> In Russia, there is no uniform method for endo-β-glucanase activity analysis that causes difficulties in assessing quality of the enzyme preparations. <...> The aim of the study was to develop such uniform method. <...> In this, we optimized a viscometric determination based on change of the relative viscosity of a substrate mixed with enzyme preparation using Ostwald capillary viscometer. <...> The following regime has been accepted: the diameter of the capillary is 0.73 mm; the temperature of hydrolysis is 30 C; the solvent is the acetate buffer (pH 4.7); time of incubation is 5, 10, 15 min in accordance with the kinetics of the enzymatic reaction; and βglucane (0.4 %) was used as substrate. <...> The carboxymethyl cellulose is shown not to be relevant so far as it gives results incomparable with those obtained with β-glucane due to estimation of the cellulase but not the β-glucanase activity, that does not correspond to the objectives of forage production. <...> The unit used in the developed method is the amount of enzyme which increases the relative substrate flow rate in 1 min-1 under standard conditions of hydrolysis. <...> The measurement of accuracy of the method was carried out according to GOST R ISO 5725-2002 (the state standards). <...> In this, 5 certified samples with different activity were prepared from a commercial sample of β-glucanase (SigmaAldrich, USA) with known activity (GLA/g). <...> Certified samples were analyzed under intermediate precision conditions with three factors changed (i.e., operator, matrix, reagents). <...> The matrices were mineral fillers, the calcium carbonate and zeolite. <...> To calculate the accuracy of the method the viscosity of certified samples was expressed in GLA units using the calibration curves. <...> Keywords: endoglucanase activity, non-starch polysaccharides, hemicellulose, viscosity, viscosimetry, β-glucane, carboxymethyl cellulose, matrix, intermediate precision, expanded uncertainty Currently, a variety of enzymatic additives used to reduce content of fodder antinutrients have been developed for animal <...>