Bacillus amyloliquefaciens CECT 5940 improves performance and gut function in broilers fed different levels of protein and/or under necrotic enteritis challenge

Abstract

Two studies were conducted to investigate the effect of <I>Bacillus amyloliquefaciens</I> CECT 5940 (BA) as a probiotic on growth performance, amino acid digestibility and bacteria population in broiler chickens under a subclinical necrotic enteritis (NE) challenge and/or fed diets with different levels of crude protein (CP). Both studies consisted of a 2 × 2 factorial arrangement of treatments with 480 Ross 308 mix-sexed broiler chickens. In study 1, treatments included 1) NE challenge (+/−), and 2) BA (1.0 × 10⁶ CFU/g of feed) supplementation (+/−). In study 2, all birds were under NE challenge, and treatments were 1) CP level (Standard/Reduced [2% less than standard]) and 2) BA (1.0 × 10⁶ CFU/g of feed) supplementation (+/−). After inducing NE infection, blood samples were taken on d 16 for uric acid evaluation, and cecal samples were collected for bacterial enumeration. In both studies, ileal digesta was collected on d 35 for nutrient digestibility evaluation. In study 1, the NE challenge reduced body weight gain (BWG), supressed feed conversion ratio (FCR) and serum uric acid levels (<I>P</I> < 0.001). Supplementation of BA increased BWG (<I>P</I> < 0.001) and reduced FCR (<I>P</I> = 0.043) across dietary treatments, regardless of challenge. <I>Bacillus</I> (<I>P</I> = 0.030) and <I>Ruminococcus</I> (<I>P</I> = 0.029) genomic DNA copy numbers and concentration of butyrate (<I>P</I> = 0.017) were higher in birds fed the diets supplemented with BA. In study 2, reduced protein (RCP) diets decreased BWG (<I>P</I> = 0.010) and uric acid levels in serum (<I>P</I> < 0.001). Supplementation of BA improved BWG (<I>P</I> = 0.001) and FCR (<I>P</I> = 0.005) and increased <I>Ruminococcus</I> numbers (<I>P</I> = 0.018) and butyrate concentration (<I>P</I> = 0.033) in the ceca, regardless of dietary CP level. Further, addition of BA reduced <I>Clostridium perfringens</I> numbers only in birds fed with RCP diets (<I>P</I> = 0.039). At d 35, BA supplemented diets showed higher apparent ileal digestibility of cystine (<I>P</I> = 0.013), valine (<I>P</I> = 0.020), and lysine (<I>P</I> = 0.014). In conclusion, this study suggests positive effects of BA supplementation in broiler diets via modulating gut microflora and improving nutrient uptake.