Efficacy of adding β-mannanase to hulled (44% CP) and dehulled (48%) soybean meal on growth performance, blood chemistry, fecal microflora and fecal noxious gas emission in growing pigs

Abstract Text: Soybean meal is widely used as the major protein source in swine diets but it occurs in several forms with varying protein content. This experiment was conducted to determine the efficacy of adding β-mannanase to hulled and dehulled corn soybean meal-based diet on parameters in growing pigs. A total of 140 growing pigs with an average BW of 25kg were allotted to pens on fed diets with main effects of CP concentration (44 vs 48%) and β-mannanase supplementation (none vs 0.05%).Treatments were arranged as a 2x2 factorial arrangement. Pigs were weighed at 0, 3 and 6 weeks of the experimental period while feed consumption was recorded on a per pen basis to calculate ADG, ADFI, and G:F. Chromium oxide (2 g/kg) was added to the diets as an indigestible marker to measure digestibility. Fresh fecal samples were obtained from at least two pigs in each pen at the end of the experiment to determine the ATTD of DM, energy, and N. One gram of the composite fecal sample from each pen was diluted with 9 mL of 1% peptone broth and then homogenized. Viable counts of bacteria were then conducted by plating serial 10-fold dilutions onto MacConkey agar plates and Lactobacilli medium III agar plates. Additionally, 150 g feces and 150 g of urine were mixed well and stored in plastic boxes. The samples were fermented for 7 d at room temperature (25°C). The concentrations of gas were determined on d 1, 3, 5, and 7 during the fermentation period. There were no interactions among the effects of CP concentration and β-mannanase addition. Hulled SBM improved (P = 0.05) the ADFI of pigs overall and tended to improve (P = 0.07) at the first 3 weeks (1731g, 1569g) compared with de-hulled SBM (1666g, 1465g). The G: F ratio improved (P < 0.05) overall as well as during 3 weeks of feeding (P < 0.05) with dehulled SBM compared with hulled SBM (0.426, 0.469 vs 0.396, 0.411). β-mannanase supplementation reduced (P < 0.05) E. coli population and tended (P = 0.09) to reduce NH₃ concentration after 24 h of fermentation. Dehulled SBM tended to reduce (P = 0.07, P = 0.08 respectively) NH₃ emission on d 3 and d 5 of fermentation. However, β-mannanase supplementation had no effect on ADG, ADFI, G:F, ATTD of nutrients as well as BUN. In conclusion, β-mannanase supplementation partially had positive effects in reducing E. coli population and NH₃ emission. Among SBM, dehulled SBM showed positive effect on feed efficiency and tendency in reducing NH₃ emission.

Keywords: mannanase, hulled, dehulled soybean meal