the invention provides pre - mixture for animal feeding comprising : a polymer or a mixture of polymers , with a content in mannose comprised between 10 % and 100 %; β - mannanase enzyme ; and an anti - binding agent ; wherein the anti - binding agent has an absorptive capacity higher than 20 %, and a bulk density which is comprised between 0 . 10 and 2 . 70 g / cm 3 . the pre - mixture of the invention diffuses better through the intestinal tract and effectively inhibits the colonization of gram negative bacteria without affecting the growth of the animal .