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.