Increasing the inclusion of dietary fiber in nursery pig diets may stimulate beneficial gut microbiota and reduce post-weaning diarrhea. However, the digestibility of nutrients and energy is decreased in high fiber diets. Nursery pigs fed diets high in fiber have been shown to have reduced ADFI and G:F.

Bacillus-based direct-fed microbials (DFM) secrete a large amount and a wide variety of fiber degrading enzymes. It is thought that feeding DFM may offset some of the negative effects of  a high fiber diet. Therefore, an experiment was conducted to test the hypothesis that addition of a Bacillus-based DFM will increase fermentation of dietary fiber and improve growth performance when fed to nursery pigs.

A total of 200 weanling pigs with an average initial body weight of 6.31 kg were used in this experiment. They were fed in two phases. Phase 1 diets (Table 1) were fed for two weeks post weaning, and Phase 2 diets (Table 2) were fed during the following 29 days. For each phase, four diets were formulated: low fiber diets and high fiber diets, each without or with DFM added. All diets were based on corn and soybean meal; the high fiber diets also contained corn distillers dried grains with solubles (DDGS) and wheat middlings.

Individual pig weights were recorded at weaning and at the conclusion of each phase. Daily allotments of feed as well as feed left in the feeder were recorded to determine feed intake. From these figures, average daily gain (ADG), average daily feed intake (ADFI), and gain:feed ratio were calculated.

At the conclusion of Phase 2, one pig per pen was sacrificed. Ileal and cecal digesta and rectal contents were collected for analysis of pH and volatile fatty acid content.

Average daily gain in Phases 1 and 2 were not affected by fiber level or DFM (Table 3). Overall ADG was greater (P ≤ 0.05) in pigs fed low fiber diets, but was not affected by DFM. Average daily feed intake was greater (P ≤ 0.05) in Phase 1 and overall for pigs fed low fiber diets, and was not affected in any phase by DFM. Gain:feed was not affected by fiber level. Gain:feed was not affected by DFM in Phase 2, but gain:feed in Phase 1 and overall was greater (P ≤ 0.05) in pigs fed diets containing DFM. No interactions were observed between dietary fiber level and DFM inclusion.

The pH of cecal digesta was lower (P ≤ 0.05) in pigs fed high fiber diets than pigs fed low fiber diets. The concentrations of acetate, propionate, total short chain fatty acids, and isovalerate in the rectal contents of pigs fed low fiber diets were less (P ≤ 0.05) than in pigs fed high fiber diets. With those exceptions, dietary fiber level did not affect pH of digesta or concentrations of fatty acids in cecal digesta or rectal contents of pigs.

No effect of DFM on pH of digesta or concentrations of fatty acids was observed. There was no interaction between dietary fiber level and DFM inclusion for any of the parameters measured.

• Phase 1 ADFI, overall ADG and ADFI, and final body weight were decreased in pigs fed the high fiber diets.
• Addition of a Bacillus-based DFM improved gain:feed in both low fiber and high fiber diets.
• Addition of the DFM did not appear to increase fermentation of dietary fiber. Therefore, the improvement in gain:feed is likely not due to more available energy in the form of VFA, but to other factors.

Table 1. Ingredient and chemical composition of phase 1 diets (as-fed basis)

¹DFM = direct-fed microbial mixture consists of 30 g of DFM mixed with 270 g of corn.

Table 2. Ingredient and chemical composition of phase 2 diets (as-fed basis)

¹DFM = direct-fed microbial mixture consists of 30 g of DFM mixed with 270 g of corn.

Table 3. Growth performance of nursery pigs fed low or high fiber diets without or with a Bacillus-based direct-fed microbial (DFM)

This report is based on unpublished research by Neil Jaworski and Hans H. Stein.