The effect on feed efficiency and immunomodulation of the yeast Pichia pastoris X-33 grown in parboiled rice effluent supplemented with glycerol byproduct from the biodiesel industry and yeast peptone dextrose medium (YPD) was evaluated in broiler chickens. The control group (Group 1) was fed with plain commercial feed while the other groups were supplemented with Saccharomyces boulardii (Group 2), P. pastoris X-33 grown in industrial effluent (Group 3) and P. pastoris X33 grown in YPD (Group 4). One-day-old female chicks were vaccinated against infectious bursal disease (IBD) and the titers of anti-IBD antibodies were measured by ELISA. Group 3 exhibited the highest mean titres of anti-IBD antibodies on days 14 and 28 (p<0,05), and at 28 days, 64% of the animals seroconverted. The specimens in Group 3 also obtained the best weight gains at 42 days of age, while on days 7, 14 and 21 they were 19%, 15%, and 8.7% higher, respectively, than the control group. The best feed conversion, which was 8.2% higher than the control group, was obtained by Group 4 at 42 days. A histopathology did not detect any undesirable effects. The researchers concluded that Pichia pastoris X-33, when grown in the effluents of the rice parboiling industry supplemented with glycerol byproduct from the biodiesel industry, increased the antibody titres elicited by an IBD vaccine and, when grown in YPD, increased feed efficiency, indicating that this it has probiotic properties.