The aim of the study was to evaluate the efficiency of two feeding systems for fattening pigs (wet and dry), taking into account their sex, on performance, nutrient digestibility, and some histological and microbiological parameters of the gut. The study was conducted on 450 fattening pigs, divided into 6 groups (n = 75) and housed in pens with 15 pigs per pen. The first three groups, divided according to sex, i.e. gilts, barrows and boars subjected to immunocastration (B-I), received complete dry feed, while the next three, divided in the same manner according to sex, were fed a fermented liquid diet. The nutritional value of the feeds, calculated on a dry weight basis, was similar for the two feeding systems in both stages of the fattening period. The best weight gains were observed in the group B-I pigs which received the liquid diet, and the poorest in the gilts fed the dry feeds. The best feed conversion ratio (FCR) was observed in the boars treated with Improvac®, especially those receiving the liquid diet. The feeding system significantly influenced the digestibility of nutrients, with higher apparent digestibility coefficients for crude protein, fat and fibre noted in the animals fed in the wet system. The liquid feeding system caused an increase in crypt depth in the colon in all groups of pigs, as well as an increase in the width of the muscular layer. A significant decrease in the total bacterial count was observed in the calcium, especially in the animals fed in the wet system.