an experiment was conduced using two hundred piglets maintained from twenty one to forty nine days of age under sanitary challenge, to know effects of mannan oligosaccharides, organic acids and probiotics about performance, gastrointestinal ph and feces score. an experimental design of randomized blocks with five treatments, ten replicates and four animals by experimental unity was used. the treatments were constituted by diet without additive, diet with mannan oligosaccharides, diet with acidifier and probiotic, diet with combination of mannan oligosaccharides, acidifier and probiotic and diet with antimicrobials. in the period from 21 to 35 days the animals fed the diet without additive presented larger feed intake, while those fed diet with acidifier and probiotic presented smaller weight gain. in the periods from 36 to 49 days and total larger weight gain for piglets with antimicrobials in relation to diet without additive and acidifier and probiotic was observed. piglets of diet without additives presented worses feed:gain relations in total period. the feces scores and ph values were not influenced by the treatments. diets supplemented with mannan oligosaccharide or mannan oligosaccharide, acidifier and probiotic propitiated similar performance for pigs from twenty one to forty nine days of age fed diet with antimicrobials.