A feeding experiment was conducted including 192 broiler chicken of the Ross 308 line. The kind of cereals used in mixtures and probiotic and prebiotic addition were experimental factors. The birds had been reared for 42 days. Broiler chickens were offered at libitum loose wheat-maize-soybean (PK) and wheat-triticale-soybean (PŻ) mixtures. The mixtures for expe rimental groups included a synbiotic containing Bacillus subtilis C-3102 bacteria and yeast (Saccharomyces cerevisiae) at the ratio of 1:1. The influence of feeding on productive results and post-slaughter value were estimated. The research results indicated that addition of synbiotic significantly influenced on body weight. Chickens were fed PK mixtures weighed by 4.1% and PŻ by 2.1% more (P ≤ 0.05) in compare to birds were fed diets without synbiotic. Use in mixtures different of cereals influenced on feed conversion ratio, especially Starter mixtures. During whole experiment didn’t observe differences FCR between feeding groups. Chickens offered rations supplemented with Bacillus subtilis C-3102 and yeast were characterised by higher dressing percentage although statistical differences (P ≤ 0.05) were found for the wheat-maize-soybean diet (75.7% vs 78.4%). An addition of the feed supplement by 6 and 16 % (diet 1 and 2, respectively) reduced the weight of chicken digestive tract and incresae (P ≤ 0.05) weight of edible offal by 5% and 13% respectively. On the basis of the results, the probiotic and prebiotic combination can be recognised as a good feed supplement which stimulates the bird growth and development when replacing feed antibiotics.

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