THE EFFECT OF THE LEVEL OF NON- DEGRADABLE PROTEIN ON DIGESTIBILITY OF NUTRITIVE SUBSTANCES IN FATTENING LAMBS**

Abstract: Results of the investigation of the effect of the level of nondegradable protein in concentrate mixtures on digestibility of nutritive substances in fattening lambs are presented in this paper. Physiological research included 18 male lambs crosses Pirot Pramenka x Württemberg x Ile de France, average body mass of approx. 35,0 kg, divided into three groups. Lambs were fed iso-protein concentrate mixtures which differed in relation to share of protein non-degradable at the rumen level: 43 % (I), 51 % (II) and 58 % (III). Trial results indicate that the level of protein adoption was not under the influence of investigated treatment, considering that digestibility coefficients were: 52,58 % : 51,30 % : 55,12%. With the increase of share of nondegradable protein in concentrate mixtures (43: 51: 58%), also tendency of increase of fat digestibility was observed: 76,13: 77,98: 87,17%, but decrease of degree of cellulose digestion: 67,40: 45,87: 22,39 % and NFE: 83,87: 76,05: 82,96%. Key words: lambs, non-degradable protein, digestibilit