Dietary Bacitracin Methylene Disalicylate Improves Growth Performance by Mediating the Gut Microbiota in Broilers

Abstract

The growth performance of livestock and poultry has always been a concern. However, much work is currently focused on the selection of breeds and diets to improve the growth performance of livestock and poultry. Furthermore, numerous studies have shown that the gut microbiota is closely related to the growth performance of livestock and poultry. At present, there are many reports on the impact of antibiotic intervention on the structure of gut microbiota. However, there are few reports on the influence of antibiotic intervention on the structure of intestinal microbes and the effect of this change on growth performance. Bacitracin methylene disalicylate (BMD) intervention changes the microbial structure in the caecum of broilers at different growth stages, as shown in this study. To further reveal the potential relationship between gut microbiota changes and growth performance caused by BMD intervention, correlation analysis was used for analysis. A total of 144 1-day-old male Cobb-Vantress were randomly divided into two groups. In addition to antibiotic-free starter mash diets, starter mash diets supplemented with 55 mg/kg BMD were also used, called the CON group and the BMD group, and lasted 28 days. (1) These study results showed that adding BMD to the diet had a significant effect on the growth performance of broilers. Compared with the CON group, the body weight of the BMD group increased significantly by 11.08% and 20.13% on Days 14 and 28, respectively (p < 0.05). Similarly, at 0−14, 14−28 and 0−28 days of age, the average daily gain of the BMD group increased significantly by 12.28%, 24.49% and 20.80%, respectively. The average daily feed intake of the BMD group increased significantly by 18.28%, 27.39% and 24.97% (p < 0.05). In addition, at 0−28 days of age, the feed conversion ratio increased significantly by 5.5% (p < 0.05). (2) Alpha diversity results show that BMD intervention has an impact on gut microbiota at different growth stages. (3) The early intervention significantly affected 7 taxa by Day 14, followed by 22 taxa by Day 28, which is similar to the results in the caecal flora. Compared with the CON group, the Christensenellaceae R-7 group had the highest linear discriminant analysis (LDA) score on Day 28. In addition, Pearson’s correlation analysis showed that the Lachnospiraceae FCS020 group was significantly negatively correlated with growth performance. In general, these results indicate that dietary supplementation of BMD has an effect on broiler gut microbiota structure and growth performance. However, changes in growth performance may be caused by the gut microbiota structure.

Keywords: bacitracin methylene disalicylate; broilers; growth performance; gut microbiota.

Figure 1

The α-diversity of the gut microbiota in the caecum of broilers in the CON and BMD groups. Features (A,E), Chao 1 (B,F), Shannon (C,G), and Simpson (D,H) were determined to elucidate the diversity and richness of the microbial community in the caecum of the broilers in the CON and BMD groups. In addition, (A–D) represent 14 days (n = 24, CON = 12, BMD = 12), and (E–H) represent 28 days (n = 23, CON = 12, BMD = 11). A two-tailed unpaired Student’s t-test was used to analysis the data, ** p < 0.01.

Figure 2

PCoA of the gut microbiota in the caecum on Day 14 (n = 24) and Day 28 (n = 23) in broilers. The caecal content of newly hatched broilers was measured on Days 14 and 28 after they were fed an unmedicated basal diet. An individual sample is represented by each data point. Based on 47 samples collected for each sampling day, PCoA was calculated (A,B) was calculated from 24 samples on each sampling day using relative abundance, and (C) was calculated from 23 samples on each sampling day using relative abundance. Statistical significance was determined using analysis of similarities (ANOSIM) and indicated in each plot.

Figure 3

In the caecum of broilers, we found phylogenetic trees of the common bacteria. In the phylogenetic tree, the shape plot on the outermost circle was made according to the T-score; the dark orange and green solid circles represent the high and low groups, respectively; the size of the dot was determined by the value of the T-score; and the coloured strips and labels were coloured according to the phylum.

Figure 4

The bacterial community composition in the caecum of Day 14 (A–D) and 28 (E–H) chickens. Newly hatched chicks were fed an unmedicated basal diet for 28 days before the luminal content was collected. The composition of the bacterial community under the intervention of antibiotics was determined based on the phylum and genus levels. Only the top 5 (phyla) and top 15 (genera) are shown.

Figure 5

On Days 14 (A) and 28 (B) are plotted. At different growth stages, the BMD group and the CON group had different abundances of bacteria. Histograms of linear discriminant analysis (LDA) scores (threshold ≥ 2).

Figure 6

The core intestinal microbiota composed of 20 bacterial genera in broilers. (A) The abundance distribution of the 20 core genera. (B) Correlation matrix showing the Spearman’s rank correlations among the collective core, which range from −1 to 1, corresponding to a strongly positive to a strongly negative correlation, respectively. (C) According to the co-occurrence network, the sold line indicated that Spearman’s rank correlation coefficient was >0.5 with a p-value < 0.05. The size of the node was related to the abundance of the genus. Colours of nodes and lines corresponded to phylum to which the genus belongs.

Figure 7

Correlation analysis between the relative abundance of different bacterial genera and the growth performance of chickens at different growth stages: (A) Day 14 and (B) Day 28. The asterisk represents its significance. * p < 0.05, ** p < 0.01.

Figure 7

Correlation analysis between the relative abundance of different bacterial genera and the growth performance of chickens at different growth stages: (A) Day 14 and (B) Day 28. The asterisk represents its significance. * p < 0.05, ** p < 0.01.