Discrepancies in porcine microbiota composition between in vivo measurements and in vitro fermentation with the modified Hohenheim Gas Test

- Microbial composition of inocula after in vitro fermentation differs from feces.
- Environmental changes during in vitro fermentation may cause microbial shifts.
- Validation of in vitro data with in vivo studies is mandatory.

In vitro gas production methods are often used to evaluate the fermentation characteristics of pig diets or their ingredients by using porcine feces as microbial inocula. The aim of the present study was to assess, whether the microbial composition of the fermentation broth after in vitro fermentation still would be representative of pig feces. Microbial composition of feces of pigs fed a standard diet was compared with microbial composition of the fermentation broth after fermenting the same pig diet using the modified Hohenheim Gas Test. Using quantitative real-time PCR, feces and fermentation broth were analyzed for total bacteria, Lactobacillus spp., Bifidobacterium spp., Enterobacteriaceae, Bacteroides-Prevotella-Porphyromonas, Clostridium Cluster IV, and Clostridium Cluster XIVa. With the exception of Clostridium Cluster XIVa, 16S copy numbers of total bacteria (P=0.020), Lactobacillus spp. (P<0.001), Enterobacteriaceae (P<0.003), Bacteroides-Prevotella-Porphyromonas (P=0.028), and Clostridium Cluster IV (P<0.001) were greater in porcine feces, while Bifidobacterium spp. was lower (P=0.001), when compared with the fermentation broth after in vitro fermentation. In conclusion, 16S copy numbers present in fermentation broth after in vitro fermentation using the modified Hohenheim Gas Test may not necessarily coincide with those determined in pigs׳ fresh feces for all bacterial groups assessed. These findings support the need for validating in vitro with in vivo studies.