Department of Poultry Sciences, College of Agriculture, Tarbiat Modarres University of Tehran, Tehran, Iran
An experiment was conducted on 400 broilers to evaluate the effects of dietary supplementation of antibiotic and probiotic on performance of birds under heat stress condition. The first group of chickens, the control group, received a diet without any antibiotic and probiotic. The second group received diet with 0.02% virginiamycin antibiotic; the two other groups were fed diets with 0.05% and 0.1% Bioplus 2B probiotic, respectively. The addition of antibiotic to the diet significantly improved body weight gain during 0–3 and 4–6 weeks (heat stress) periods as compared to the control and 0.05% probiotic-supplemented groups (P<0.05). Feed intake of different groups did not differ significantly (P>0.05). Addition of antibiotic or various levels of probiotic to the diet significantly improved feed conversion ratio during 4–6 weeks (heat stress) period as compared to the control group (P<0.05). Supplementation of diet with antibiotic had no significant effect on antibody production against sheep red blood cells (SRBC), Newcastle disease virus (NDV) vaccine, white blood cell (WBC) count, heterophil to lymphocyte ratio (H/L), serum cholesterol and haemoglobin content (P>0.05). Supplementation of diet with various levels of probiotic had no significant effect on antibody titer against SRBC, NDV vaccine and haemoglobin content (P>0.05). However, supplementation of diet with 0.1% probiotic significantly increased WBC count and decreased H/L as compared to the control group (P<0.05) which is important in reduction of stress effects on birds.