The aim of this paper was to recognise the effect of feed modification, with standard feeding enriched with mineral-humine preparations and antioxidants (vit. A + E) on the activity of lysozyme and cystatin. Experimental materials were eggs from 3 groups of Tetra SL laying hens: A control group with standard feeding (17% protein, 2700 kcal/kg); B with addition vitamins A (10 000 unit/kg) and E (20 mg/kg); C with addition 2% humobentofet (HB), humocarbovit (HK) and vitamins A +E. Experiment occurred fresh Eggs stored 4 weeks at 15°C. Lysozyme activity was analysed spectrophotometrically by measuring changes in optical density of Micrococcus lysodeicticus solution during enzymatic lysozyme reaction. Inhibitory activity of cystatin was measured according to Nishida et al  and Siewiński . Differential feeding significantly affected the level of cystatin activity in fresh egg white. In control group (A) this activity was the highest (421 units/100 mg protein). Lower cystatin activity was estimated in eggs from groups B and C laid by hens with enriched feeding. In group C this activity was lower on about 26.2% and in group B on 26%in comparison to control group. This protein did not have storage stability. The activity of cystatin in all samples decreased during storage for 4 weeks. The highest decrease of cystatin activity (35% related to fresh egg white) was analysed in group A. Feeding modification had a positive effect on lysozyme activity in fresh egg white. The level of lysozyme enzymatic activity was higher in groups B and C than in control group. The highest lysozyme activity was obtained in egg white derivated from layers fed with vitamins A and E (group B).
laying hens, eggs, cystatin, lysozyme, cysteine protease inhibitors, humobentofet, humocarbovite