The aim of the present study was to compare the effect of Lactobacillus casei and a commercial mixed combination of fruit juice that included Garcinia mangostana fruit extract on body weight gain from 7 to 90 days of age, on the antibody response 23 days after vaccination against Newcastle disease virus (NDV), and on the mortality in fighting roosters. Fifty-four 7-day-old birds were randomly distributed into three groups (treated with L. casei, G. mangostana, and saline solution [LC, GM, and SS groups, respectively]) of 18 animals each; all birds were orally treated daily. At 60 and 90 days, the LC group showed the highest body weight gain compared with the other two groups (P<.01). The mean levels of antibody to NDV were significantly higher in the GM group compared with the LC and SS groups (P<.05). Throughout the study the percentages of mortality were 5.55%, 0%, and 22.22% for the LC, GM, and SS groups, respectively. The results indicate that L. casei and the commercial mangosteen dietary supplement intake, compared with the control group, induce beneficial effects in fighting roosters--L. casei on weight gain and the commercial mixed combination of fruit juice with G. mangostana fruit extract on humoral immune response--and both showed none or very low mortality.