Effects of Bacillus-Based Direct-Fed Microbials on Growth and Gut Health of Nursery Pigs

The objective of this study was to determine the effects of Bacillus-based direct-fed microbials (DFM) on growth performance, gut health, immune status, and oxidative stress status in nursery pigs. Pigs (180 barrows and 180 gilts) at 21 d of age and 6.26 ± 1.02 kg BW were randomly assigned to 3 treatments based on a randomized complete block design with sex and initial BW as blocks: 1) Basal diet (CON); 2) Basal diet + DFM based on 1 Bacillus species (3.34 x 10⁹ CFU/kg feed) (DFM-1); 3) Basal diet + DFM based on 2 Bacillus species (1.28 x 10⁹ CFU/kg feed) (DFM-2). Pigs were distributed into 30 pens per treatment with 4 pigs per pen. Pen was the experimental unit and proc MIXED of SAS was used for statistical analysis using treatment and sex as fixed effects and BW block as a random effect. Pigs were given ad libitum access to feed and water for 42 d with d 1 to 14 representing phase 1 and d 15 to 42 representing phase 2. Feed intake and BW were measured at the beginning and end of each phase to calculate ADG, ADFI, and G:F. At d 42, 8 pigs (1 per pen) per treatment (4 barrows and 4 gilts) were euthanized for sample collection. Serum and jejunal mucosal tissues were obtained to measure tumor necrosis factor α (TNF-α), immunoglobulins G and A (IgG and IgA), protein carbonyl (PC) and malondialdehyde (MDA). Jejunal tissues were obtained to measure tight junction proteins (claudin, occludin, and ZO-1). The ADG was greater (P < 0.05) in the DFM-1 (550 and 427 g/d) and DFM-2 (546 and 424 g/d) compared to the CON (503 and 392 g/d) for both phase 2 and the overall experimental period, respectively. Overall ADFI was increased (P < 0.05) in the DFM-1 (552 g/d) and DFM-2 (555 g/d) compared to the CON (516 g/d), although there were no effects on G:F. The DFM-1 had higher (P < 0.05) ZO-1 than the CON. The DFM-1 had higher (P < 0.05) claudin and ZO-1 than the DFM-2. There were no differences in TNF-α, IgG, IgA, PC, or MDA concentrations in serum and jejunal mucosa among treatments. In conclusion, both Bacillus-based DFMs improved growth of nursery pigs primarily by increasing feed intake whereas the DFM with 1 Bacillus strain additionally improved gut integrity without affecting immune or oxidative stress status in the small intestine.