A new in vitro model of the adult pig colon microbiome: application to the study of feed ingredients.

Background: There is an intricate relationship between pig nutrition and gut microbiome. For technical, cost and societal reasons, in vitro gut models can be advantageously used as an alternative to in vivo experiments to perform mechanistic studies on the interactions between gut microbes and nutrients. In this context, the aim of the present study was to develop a new in vitro model of the healthy adult pig colon integrating both luminal and mucosal microenvironments. The model was further used to evaluate feed ingredients (lactose and lactose + sucrose). Gut Microbiota composition and metabolic activities were followed by 16S Metabarcoding and short chain fatty acid (SCFA) / gas measurement, respectively. Then, the effect of the both feedstuffs on skatole production, responsible for boar taint in male pigs, was also investigated.

Results: Based on in vivo data, the new MPigut-IVM was set-up to reproduce the main physicochemical (pH, transit time, self-maintained anaerobiosis), nutritional (composition of ileal effluents, bile salts) and microbial (lumen and mucus-associated microbiota) parameters of the large intestine in healthy adult pigs. The model was validated through in vitro-in vivo comparisons regarding SCFA concentrations and bacterial profiles at the phylum and family levels. Lactose and lactose + sucrose had no significant impact on SCFAs but increased gas production (P < 0.01 with lactose). Both sugars, particularly lactose + sucrose, tended to reduce skatole concentrations while increasing indole levels (P > 0.05). This was associated to a slight reduction of the numbers of skatole-producing bacteria Olsenella scatoligenes (P > 0.05). Both feed ingredients induced a decrease in bacterial α-diversity (P < 0.05).

Conclusion: Despite obvious limitations such as lack of host interactions, the adult MPigut-IVM represents a powerful platform for Microbiome studies in the pig colonic environment. In Line with the 3R regulations, this in vitro model can be useful to perform preliminary screening of innovative feed strategies to improve pig health and help to elucidate their mechanisms of action in relation with gut microbiota, taking into account inter-individual variabilities.