Effect of pelleting temperature and probiotic supplementation on growth performance and immune function of broilers fed maize/soy-based diets

The aim of the present experiment was to examine the effect of pelleting temperature and a probiotic supplementation based on three Bacillus subtilis strains on growth performance and the immune function of broilers fed maize/soy-based diets. The experimental design was a 2 × 3 factorial arrangement of treatments evaluating two levels of probiotic supplementation (without or with 1.5 × 105 cfu/g feed) and three pelleting temperatures (75, 85 and 90 °C). Each treatment was fed ad libitum to 8 pens of 22 male broilers, in both the starter (1-21 day) and the grower (22-42 day) phases. On day 21 and 42, 6 birds per treatment were randomly selected to measure blood immunoglobulin M (IgM) and immunoglobulin A (IgA), production of reactive oxygen intermediates (ROI) and duodenal secretory IgA. Data were analysed by two-way analysis of variance (ANOVA) using the general linear model (GLM) procedure of statistical analysis software (SAS). During the starter phase (1-21 day), pelleting temperature had no effect (P>0.05) on broiler performance. However, probiotic supplementation tended to reduce feed intake (P=0.055) compared to unsupplemented diets with no effect (P>0.05) on weight gain or feed conversion. During the finisher phase (22-42 day) and over the entire period (1-42 day) pelleting temperature at 85 °C reduced (P<0.05) weight gain compared to those fed diet pelleted at 75 or 90 °C. Probiotic supplementation reduced (P<0.05) feed intake and improved (P<0.05) feed conversion. No interactions (P>0.05) were observed for any of the measured performance parameters during the overall period. There was no effect (P>0.05) of dietary treatments on the measured blood IgM, IgA and ROI. Probiotic supplementation and pelleting temperatures (85 and 90 °C) increased (P<0.05) the concentration of secretory IgA in the duodenum on day 21. On day 42 an interaction (P<0.01) between probiotic and pelleting temperature was observed for the duodenal concentration of secretory IgA. In probiotic supplemented diets, pelleting temperature at 90 °C reduced the concentration of secretory IgA compared to diets pelleted at 75 or 85 °C. In conclusion, the results of this study suggest that increased pelleting temperature and probiotic supplementation stimulate duodenal secretory IgA production during the starter phase (1-21 day). Furthermore, over the entire period (1-42 day), probiotic supplementation based on three Bacillus subtilis strains improved feed conversion ratio in broilers fed maize/soy diets, regardless of the pelleting temperature used.