Performance and gut microbiome diversity of broilers supplemented with a single strain Bacillus subtilis probiotic and a multi-complex carbohydrase

Abstract

The use of antimicrobial growth promoters in broiler feed used to be and still is common practice in several parts of the world. However, due to the risk of microbial resistance building up, several countries have banned the use of antimicrobial growth promoters (AGP) and in other countries this movement away from AGP is driven by consumer demands. Unfortunately, as seen in Europe, the removal of AGP from broiler feed is not a simple process, thus several alternative options have since been investigated. The purpose of the study was to evaluate the benefits, if any, of adding a single strain Bacillus subtilis, probiotic product, either alone or in combination, with a multi complex carbohydrase (NSPase) to the diet of broilers. The study was conducted in a fully environmentally controlled, semi-commercial broiler house. The house contained 96 pens in total, all set up in one line from the front to the back of the house. The pens were surrounded by commercially produced broilers throughout the duration of the trial, to simulate commercial conditions as far as possible. Two thousand three hundred and fifty Ross 308 male broiler birds were feather-sexed and randomly distributed throughout the pens, 24 broilers per pen at a stocking density of 22.22 birds/m2. All broilers received similar typical South African maize-soya diets throughout the study. Diets were treated with antibiotic growth promoters (AGP) and / or probiotic and / or NSPase to create six treatments as follows: Negative Control: Basal diet (without AGP, probiotic and NSPase), Positive Control: Basal diet with AGP, Treatment 1: Basal diet with NSPase and AGP, Treatment 2: Basal diet with NSPase, Treatment 3: Basal diet with probiotic, Treatment 4: Basal diet with probiotic and NSPase. Broiler performance was measured periodically, coinciding with feeding phases, in terms of body weight (BW), feed intake (FI) and feed conversion ratio (FCR) from day-old to 35 days-of-age. Two birds per pen were culled on day 25. One bird was used for macroscopic gut health scoring and one to collect caecal samples for quantification of the microbiome. Broilers that received AGP treatments had a significantly higher BW at 28 days compared to broilers that received probiotic (without NSPase) and NSPase (without AGP) diets. Broilers that received the probiotic (without NSPase) diet had a significantly lower FCR in the final week of the study when compared to both treatments containing AGP. At the end of the study there were no significant differences between any of the treatments for the performance parameters measured including mortalities. Treatment 3 had significantly higher percentage abundance of the phylum Tenericutes when compared to the positive control. When compared to the positive control, Treatment 3 also had significantly higher percentage abundance in both the Bacillales and RF39 orders. There was a significant difference in the average percentage abundance between Treatment 3 and Positive Control in the Bacillaceae_Unknown, Clostridium, Lachnospiraceae_Unknown, Anaerostipes, Campylobacter and RF39_Unknown genera. Treatment 3 had significantly higher percentage abundance in Bacillaceae_Unknown, Anaerostipes and RF39_Unknown genera, whereas Positive Control had significantly higher percentage abundance of Clostridium, Lachnospiraceae_Unknown and Campylobacter. It could not be concluded whether the probiotic, alone or in combination with a NSPase, can be successfully used to replace AGP in commercial broiler production.