Effects of meat and bone meal, phytase and antibiotics on growth performance in broiler chickens during necrotic enteritis challenge

Meat and bone meal (MBM) is a valuable source of protein, calcium and available phosphorus for broiler diets (Anwar et al., 2016). The use of MBM in broiler diets at levels above 50 g/kg minimizes the need for inclusion of inorganic P, thus reducing feed cost. Potential indigestibility of protein in MBM (Kim et al., 2012) may act as a predisposing factor for necrotic enteritis (NE). Increased production of nitrogenous bacterial metabolites including amines and ammonia in the hindgut may increase pH and favour proliferation of Clostridium perfringens. A study was designed to investigate the hypothesis that superdosing with phytase in meat and bone meal free diets might enhance growth performance during the challenge period with necrotic enteritis compared with diets containing MBM. The experiment used 672 Ross 308 male broilers in a completely randomized design with a factorial arrangement of treatments. Factors were meat and bone meal (no or yes), antibiotic (zinc bacitracin, 100 mg/kg in starter (S), grower (G) and 50 mg/kg in finisher (F) with salinomycin, 60 mg/kg in S, G, F), phytase (500 using 500 matrix or 1500 using 500 FTU/kg matrix) (Quantum BlueTM, AB Vista, Malborough, UK) and MBM (none or 60, 50 and 50 g/kg in S, G, F). The birds were fed wheat-SBM-canola meal based diets in which MBM partially replaced soybean meal and completely replaced limestone throughout the experiment, but completely replaced mono and di-calcium phosphates only during the starter and grower phases of the study. There were 14 birds per pen and 6 replicates per treatment. All birds were challenged with 5000 unattenuated sporulated oocysts each of Eimeria acervulina, E. brunetti and E. maxima (Bioproperties Pty Ltd) on d 9, and 10⁸ CFU of C. perfringens Strain EHE-NE18 (known to express NetB toxin (CSIRO) on d 14 and again on d 15. Inclusion of MBM in the diets improved body weight gain on d 7 (pre-challenge; P < 0.05). However on d 21 (post-challenge) and d 28, MBM inclusion decreased BW relative to those fed MBM-free diets (P < 0.05). No MBM effect was detected on BW on d 35 or d 42 (P > 0.05). Interactions between the phytase level and the presence of antibiotics were detected for BW on every weigh day (P < 0.001), indicating a positive effect of phytase superdose on BW in the presence of antibiotic (lower incidence of NE after challenge). Similarly, phytase by antibiotic interactions were detected for FCR on d 21, d 28, d 35 and d 42 (P < 0.01) indicating a greater effect of antibiotics in decreasing FCR in the presence of superdose phytase. On d 42, (across MBM levels), FCR of birds fed no antibiotics was 1.528 with 500 FTU phytase and 1.623 with 1500 FTU phytase whereas with antibiotics FCR was 1.519 with 500 FTU phytase and 1.553 with 1500 FTU phytase. No MBM by phytase interactions were detected for BW or FCR at any time during the experiment (P > 0.05). The results suggest that superdosing with phytase may result in the release of additional nutrients, such as calcium that may influence bacterial growth in the hindgut through elevation of pH. In the presence of antibiotics, birds were protected from NE. The greatest weight gain and lowest FCR was with 1500 FTU phytase, MBM with antibiotic. If NE challenge is expected, antibiotics and full matrix value for the dose of phytase should be used to minimize excess calcium in the hindgut. In conclusion, superdosing phytase improves growth performance of broiler chickens growing under optimum conditions.

ACKNOWLEDGEMENTS: This study was funded by AB Vista Feed Ingredients.