Full-fat insect meals were used in young turkeys feeding as feed additives to exert beneficial changes in the intestinal bacterial ecosystem functioning as well as in the immune and antioxidant systems. Two full-fat insect flours obtained from Tenebrio molitor (TM) and Hermetia illucens (HI) insects were added to the base diet (C) in the amount of 3 g/kg and compared to the control and to the effects following common monensin (MON) addition (dietary treatments: C, MON, TM, and HI). Although, the addition of full-fat insect meals to the diet didn’t improve performance results such as monensin, it does exerted anti-inflammatory, immunostimulatory and antioxidant changes in turkeys’ blood. The HI and TM dietary treatments caused beneficial reduction in the blood total cholesterol content as well as increase in phosphorus which was not noted in MON treatment. The results indicated that in comparison to the control diet without any additives, the MON, TM and HI additives showed non-selective bacteriostatic properties, without adverse intensification of protein fermentation and pH digesta rise in the caeca of young turkeys. The addition of TM and HI similar as MON reduced the enzymatic activity of caecal microbiota, and decreased caecal concentration of all short-chain fatty acids, except butyric one. The caecal ammonia and dry matter concentration, and pH value of digesta were not affected by dietary treatments.