Interpretive Summary: Effects of Bacillus amyloliquefaciens and Bacillus subtilis on ileal digestibility of AA and total tract digestibility of CP and gross energy in diets fed to growing pigs.
By: Anne Wallace
Direct-fed microbials (DFM) are live yeasts or bacteria that may serve as substitutes for antibiotics in animal feed. Of particular interest in this study published in the February 2019 Journal of Animal Science was the potential for DFM to promote the growth of pigs by improving the digestibility of feed. Previous studies suggest that Bacillus DFM may improve feed efficiency, however, there are a multitude of Bacillus strains which may have varying effects. The research team therefore chose to evaluate two specific strains: B. amyloliquefaciens (DSM 25840) and B. subtilis (DSM 25841).
A total of 24 barrows with surgically fitted T-cannula ports were used in this study. Three diets (all nutritionally adequate corn and soybean based) included: (1) control diet with no added DFM, (2) diet supplemented with B. amyloliquefaciens, and (3) diet supplemented with B. subtilis. Ileal digesta and fecal and urine samples were collected and analyzed during the study period.
The authors reported that the two strains of Bacillus they tested did not affect the intake or excretion of nitrogen in this study. The apparent total tract digestibility (ATTD) of crude protein (CP) was also no different between the DFM and control diets. However, apparent ileal digestibility (AID) of CP was reduced in pigs fed B. subtilis, suggesting a greater apparently hindgut digestibility compared to the B. amyloliquefaciens or control diets.
The results of this study support that there are varying effects of Bacillus DFM on feed digestibility based on strain. The AID of gross energy (GE) was also found to be increased in the B. amyloliquefaciens diet, compared to B. subtilis and control. Also considering that AID of CP was reduced in pigs fed B. subtilis but not B. amyloliquefaciens suggests a larger study involving more Bacillus strains may need be conducted to evaluate for most effective strain(s). Overall, expanded studies looking into the effects of Bacillus DFM on digestibility is warranted.
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