Dietary supplementation with Bacillus subtilis KC1 alleviates the negative effects of Mycoplasma gallisepticum on growth performance and amino acid metabolism of broiler chickens
The aim of this study was to explore whether, and if so, how Bacillus subtilis KC1 can enhance the growth performance of broilers that have been adversely affected by Mycoplasma gallisepticum (MG) infection. A total of 96 1-day-old male broilers were randomly divided into 4 groups: the control group (basal diet), the MG group (basal diet + MG challenge), the Bacillus subtilis KC1 group (basal diet + Bacillus subtilis KC1 supplementation), the Bacillus subtilis KC1 + MG group (basal diet + Bacillus subtilis KC1 supplementation + MG challenge). The trial lasted 42 days, and the results showed that the MG group had significantly reduced body weight and average daily gain, as well as increased feed conversion ratio of broilers, compared to the control group. Dietary supplementation with Bacillus subtilis KC1 significantly improved the growth performance of MG-infected broilers. In addition, dietary supplementation with Bacillus subtilis KC1 significantly improved oxidative stress and inflammatory response markers, characterized by increased superoxide dismutase levels and reduced levels of malondialdehyde, interleukin-1ß, and tumor necrosis factor-a. Furthermore, both metabolomics and transcriptomics analyses indicated that MG infection markedly disrupted amino acid metabolism in broilers, whereas Bacillus subtilis KC1 supplementation alleviated the abnormal amino acid metabolism caused by MG infection. These results suggested that Bacillus subtilis KC1 may alleviate the poor growth performance caused by MG infection in broilers by improving amino acid metabolism. Overall design: A total of 96 one-day-old male AA broilers with an initial average body weight (39.29 ± 0.54 g) were selected and divided into 4 groups: (1) chickens were fed a control diet (Con); (2) chickens were fed a control diet supplemented with 108 CFU/kg of Bacillus subtilis KC1 (KC); (3) chickens were fed a control diet and challenged with MGat day 14 (MG); and (4) chickens were fed a control diet supplemented with 108 CFU/kg of Bacillus subtilis KC1, and further challenged with MG at day 14 (MG_KC). Each treatment was replicated 3 times, with 8 chickens per replicate. All diets were formulated to meet the National Research Council and Chinese chicken feeding standards (NY/T-33–2004) [12,13]. A single-layer, three-dimensional chicken coop was used. Temperature was gradually reduced by 2 °C per week from 33 °C to 23 °C and then kept constant.Lung, liver and ileum samples were collected (3 samples per treatment, 1 per replicate) at day 42. Total RNA was extracted using TRIzol reagent (ET101-01-V2, Beijing TransGen Biotech Co., Ltd, Beijing, China). The RNA concentration and integrity were detected using a Fragment Analyzer (Agilent, California, USA). RNA samples that complied with the criteria of having a concentration of more than 40 ng/µL, an integrity value greater than 7.0, and a total content of 1 µg or more were chosen for further experimentation. Transcriptomic sequencing was completed by BGI.