The objective of this experiment was to evaluate the effects of a multi-strain Bacillus subtilis-based direct-fed microbial (DFM) on weanling pig growth performance, nutrient digestibility, immunity markers, intestinal morphology, and microbial communities. A study was conducted to test the hypothesis that DFM supplemented pigs would have greater nutrient digestibility and improvements in specific indicators of health status. Eighty pigs, of equal number of barrows and gilts (initial BW: 7.0 ± 0.60 kg), weaned at 21 ± 1 days of age were randomly allotted to sixteen pens, with five pigs per pen. Two dietary treatments were implemented, a basal control (CON) and a control plus DFM (DFM). Both diets were corn, soybean meal, and distillers dried grains based and were formulated to meet or exceed all nutrient requirements and manufactured on site. Diets were fed for 42 days. Growth performance was recorded on a weekly basis. On d 21 and 42 of the experiment, one pig per pen was randomly selected and euthanized, with equal number of males and females represented. Blood samples were collected prior to euthanasia for assessment of plasma concentrations of immunoglobin A (IgA) and intestinal fatty acid binding protein. Segments of the gastrointestinal tract including duodenum, jejunum, ileum, ascending and distal colon were removed for analysis of nutrient digestibility, intestinal morphology, microbial communities, and concentrations of interleukin 6, interleukin 10 (IL-10), and tumor necrosis factor alpha. Overall growth performance did not differ between DFM and CON. Overall means ± SD were 0.51 ± 0.05 kg/d, 0.79 ± 0.05 kg/d and 0.66 ± 0.05 for ADG, ADFI, and G:F, respectively. Compared to pigs fed CON, overall digestibility of AA within the jejunum tended to be greater for tryptophan (P = 0.06), methionine (P = 0.10), and cysteine (P = 0.12) for pigs fed DFM. The pH of contents in ascending colon, a possible indicator of varied fiber digestion, did not differ. Apparent total tract nitrogen and energy digestibility did not differ between DFM and CON on d 21 or 42. Compared to CON, overall jejunal villus height was greater (P = 0.02) (422 vs. 385 ± 10 [mu]m, respectively) and ascending colon crypt depth tended to be greater (P = 0.10) on d 21 (373 vs. 337 ± 14 [mu]m, respectively). Compared to CON, DFM tended to increase IgA (P = 0.06) on d 21 (0.34 vs. 0.54 ± 0.07 mg/mL, respectively) and tended to increase IL-10 (P = 0.12) on d 42 (133 vs. 237 ± 49 pg/mL, respectively). Addition of a multi-strain Bacillus subtilis-based DFM appears to impact select amino acid digestibility within the jejunum. Improvements in digestibility may be related to the DFMs benefit on weanling pig health status, observed via differences in intestinal morphology and specific immunity markers.
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