The Use of Bacillus-based Direct-fed Microbials to Improve Growth Performance and Gut Health of Nursery Pig

Concerns about the use of antibiotics as growth promotors in livestock production have led to the removal of many antimicrobial growth promotors from livestock production. The use of direct-fed microbials (DFMs) as an antibiotic alternative has generated significant interest over the last decade. However, research findings in pigs have been extremely variable and the novel strain Bacillus subtilis 29784 has yet to be evaluated in pigs. Therefore, to address the current issue, three experiments were conducted.;The objective of experiment 1 was to determine the effects of Bacillus-based DFMs on growth performance, gut health, immune status, and oxidative stress status in nursery pigs. Three-hundred and sixty nursery pigs were randomly assigned to 1 of 3 treatments based on a randomized complete block design, with sex and initial body weight as blocks: 1) Basal diet (CON); 2) Basal diet + DFM Bacillus subtilis 29784 (DFM-1); 3) Basal diet + DFM based on Bacillus subtilis and Bacillus licheniformis (DFM-2). Both DFM treatments improved (P < 0.05) average daily gain (ADG) compared to the CON from d 15 to 42 and during the overall experimental period. Both DFM treatments also improved (P < 0.05) average daily feed intake (ADFI) compared to the CON during the overall experimental period. Both DFM treatments tended to (P = 0.090) lower the pH in colon digesta. In addition to improvements in growth, DFM-1 increased (P < 0.05) concentrations of tight junction protein zonula occludens-1 (ZO-1) compared to the CON and DFM-2 treatments.;The objective of experiment 2 was to determine the optimal dose of Bacillus subtilis 29784 to improve growth performance of nursery pigs. Fifty-four newly weaned piglets were randomly allotted to 1 of 3 treatments: 1) T1: Basal diet; 2) T2: T1 + Bacillus subtilis (1.0 x 10 8 CFU/kg feed); 3) T3: T1 + Bacillus subtilis (2.5 x 108 CFU/kg feed). Days 1 to 14 were considered phase 1 and days 15 to 42 were considered phase 2. Increasing concentrations of Bacillus subtilis had a quadratic effect (P < 0.05) on d 14 BW with the greatest d 14 BW (10.1 kg) achieved with T2. From d 1 to 14, the concentrations of Bacillus subtilis tended to quadratically affect both ADG ( P = 0.064) and ADFI (P = 0.097) with the highest phase 1 ADG (242 g/d) and ADFI (259 g/d) achieved with T2. Concentration of Bacillus subtilis did not affect G:F from d 1 to 14, d 15 to 42, or the overall experimental period. No effects of Bacillus subtilis concentrations on growth performance were observed from d 15 to 42 or the overall experimental period. The concentration of Bacillus subtilis did not affect fecal scores.;The objective of experiment 3 was to determine the effects of Bacillus subtilis 29784 on gut health and prevention of post-weaning diarrhea caused by F18+ Escherichia coli. Forty nursery pigs were randomly allotted to 1 of 4 treatments with initial BW as a blocking factor: 1) NC: a diet with no additive and no F18+ Escherichia coli challenge; 2) PC: a diet with no additive and F18+ Escherichia coli challenge; 3) AGP: PC + antibiotics (CTC 100 and Denagard for phase 1 and Mecadox for phase 2) and ZnO; 4) PRO: PC + Bacillus subtilis 29784. The F18+ Escherichia coli challenge was administered on d 7. Body weights were not affected by treatment during wk 1, 2 or 3. During wk 4, both AGP and PRO had higher body weights than PC ( P < 0.05) but were not different from NC (Table 2). No effects of treatment were observed on ADG during the entire experimental period. During wk 2, AGP and PRO improved (P < 0.05) ADFI compared to PC but not compared to NC (Table 2). There were no differences in ADFI among treatments during wk 3. However, during wk 4, all challenged treatments (PC, AGP, and PRO) had decreased (P < 0.05) ADFI compared to NC (Table 2). No effects of treatment were observed on G:F during wk 1, 2, or 4. However, during wk 3, the challenged treatments (PC, AGP, PRO) tended to have higher (P = 0.095) G:F than NC (Table 2). The PRO and AGP tended to (P = 0.097) have lower protein carbonyl than PC which was an indicator of improved oxidative stress status. Contrary to the hypothesis, The PRO did not prevent postweaning diarrhea caused by F18+ Escherichia coli..;In conclusion, experiments 1 and 3 demonstrated that Bacillus -based DFMs can improve growth performance and gut health of nursery pigs in natural exposure conditions and may reduce the relative abundance of pathogenic bacteria during a pathogen challenge. Experiment 2 demonstrated that in order to achieve optimal growth performance, Bacillus subtilis 29784 should be supplemented at 1.0 x 108 CFU/kg feed. Overall, these experiments show that Bacillus-based DFMs could be a potential alternative to antibiotics although more research is needed.