In the present work we evaluated the effects of probiotic strains administration in pigs. On the 35th day of age, 30 pigs were distributed into 2 groups: the non-treated control group (initial average BW: 8.3 +/- 0.6 kg) and a probiotic supplemented fed group (initial average BW: 8.7 +/- 0.4 kg). Each experimental group was fed ad libitum on a commercial diet with free access to tap water for 35 days. A mixed probiotic culture (10(8) CFU/ml) was orally delivered, every day, to the animals of the probiotic supplemented fed group. Body weight (BW), feed intake (Fl), efficiency (BW: Feed), and faecal microflora, were studied before and throughout the experimental trial. At the end of the fifth week, 5 animals of each dietary treatment were slaughtered and intestinal samples were taken for histology. The results obtained showed that the group receiving probiotic bacteria exhibited lower Fl values and better efficiency than control group (P <= 0.05), but mean final BW values were not significantly different. Only significant changes (P <= 0.05) were found in enterobacteria population between control and probiotic supplemented fed group during the experimental period. By histological techniques it was observed that the treatment group has intestinal morphological structures more preserved than control group. These results suggest that probiotic bacteria administrated in this study could be used widespread as a way to improve growth performance parameters of animals avoiding the use of antibiotics as growth-promoting factors. (C) 2009, The Society for Biotechnology, japan. All rights reserved.