Dose-Dependent Effects of Supplementing a Two-Strain Bacillus subtilis Probiotic on Growth Performance, Blood Parameters, Fecal Metabolites, and Microbiome in Nursery Pigs

Abstract

This experiment was conducted to evaluate the effects of dietary supplementation level of a two-strain Bacillus subtilis probiotic on growth performance, blood parameters, fecal metabolites, and microbiome in nursery pigs. A total of 54 weaned piglets were allotted to three treatments in three replicate pens with six pigs/pen for a 28 d feeding trial. The treatments were as follows: control: no probiotic supplementation; Pro1x: B. subtilis supplementation at 1.875 × 10⁵ CFU/g diet; and Pro10x: B. subtilis supplementation at 1.875 × 10⁶ CFU/g diet. Body weight at d 14 postweaning (p = 0.06) and average daily gain for d 0 to 14 postweaning (p < 0.05) were greater in the Pro1x treatment than in the other treatments. Blood glucose levels were greater in both probiotic treatments than in the control treatment at d 14 postweaning (p < 0.05). In the fecal short-chain fatty acid (SCFA) concentrations, the butyrate concentrations were greater in the Pro1x treatment than in the other treatments (p < 0.05), and the acetate, propionate, and total SCFA concentrations were greater in the Pro1x treatment than in the Pro10x treatment (p < 0.05). The beta diversity of fecal microbiome composition at d 14 postweaning based on Unweighted Unifrac analysis was dissimilar between the Pro1x and Pro10x treatments (p < 0.05). In conclusion, dietary B. subtilis supplementation of two strains selected to reduce effects of pathogenic Escherichia coli to nursery diets at 1.875 × 10⁵ CFU/g diet improved the growth rate in the early postweaning period, increased fecal SCFA concentrations and altered the fecal microbial community composition. A higher dose of B. subtilis did not improve the performance parameters over those of the control piglets.

Keywords: Bacillus subtilis; growth; pigs; short-chain fatty acids; supplementation level; weaning.

Figure 1

Taxa summary plot by variable. (A) Day of postweaning (d 14 and 28 postweaning). (B) Dietary treatment (n = 6 pens per treatment). Treatments: (1) control: no probiotic supplementation, (2) Pro1x: B. subtilis supplementation at 1.875 × 10⁵ CFU/g diet, and (3) Pro10x: B. subtilis supplementation at 1.875 × 10⁶ CFU/g diet.

Figure 2

Beta diversity indexes. Bray–Curtis dissimilarity (A,B) and Jaccard index (C,D) of fecal samples from swine in two different days of postweaning ((A,C); n = 18 per day of postweaning) and three different treatments ((B,D); n = 6 per treatment). (A) Bray–Curtis dissimilarity by day of postweaning (d 14 and 28 postweaning). (B) Bray–Curtis dissimilarity by dietary treatment. (C) Jaccard index by day of postweaning (d 14 and 28 postweaning). (D) Jaccard index by dietary treatment. Treatments: (1) control: no probiotic supplementation, (2) Pro1x: B. subtilis supplementation at 1.875 × 10⁵ CFU/g diet, and (3) Pro10x: B. subtilis supplementation at 1.875 × 10⁶ CFU/g diet.

Figure 3

Alpha and beta diversity in feces of nursery pigs with Unweighted Unifrac analysis and Pielou’s Evenness. (A) beta diversity based on Unweighted Unifrac analysis at d 14 postweaning and a significant difference (p < 0.05) between Pro1x and Pro10x treatments. (B) Alpha diversity based on Pielou’s Evenness at d 28 postweaning and a greater evenness (p < 0.05) in fecal microbiome in Pro1x treatment than Pro10x treatment. Treatments: (1) control: no probiotic supplementation, (2) Pro1x: B. subtilis supplementation at 1.875 × 10⁵ CFU/g diet, and (3) Pro10x: B. subtilis supplementation at 1.875 × 10⁶ CFU/g diet. Gray dots are outliers.