Effect of cellobiose supplementation on in vitro fermentation activity and bacterial numbers of porcine inocula
Studies on the impact of feed additives on gut microbiota composition and activity and its association with gut health have increasingly gained interest. Beneficial effects of fermentable carbohydrates have been acknowledged, especially with regard to the production of short‐chain fatty acids (SCFA), which are known for their trophic and health‐promoting effects in the gastrointestinal tract (GIT) of pigs (Cummings & Macfarlane, 1991). On the other hand, branched‐chain fatty acids (Cummings & Macfarlane, 1991) in addition to amines, amides and ammonia represent potential fermentation products of dietary protein which may cause detrimental effects on intestinal health and microbial composition, possibly causing diarrhoea (Dong et al., 1996). Yet, in combination with a larger amount of fermentable carbohydrates non‐digested protein accumulating in the large intestine will stimulate bacterial proliferation, thereby enhancing SCFA production, as reviewed by Millet, Van Oeckel, Aluwé, Delezie, and De Brabander (2010). Thus, the supply of a sufficient amount of fermentable carbohydrates in addition to lower protein contents in the diet may inhibit proteolytic fermentation and its resulting metabolites. Within this regard, the modified Hohenheim gas test (HGT; Rink, Bauer, Eklund, Hartung, & Mosenthin, 2011) was used in the present study to evaluate potential prebiotic properties of 4‐β‐D‐glucopyranosyl‐D‐glucopyranose, known as “cellobiose.” The disaccharide is not hydrolysed by intestinal disaccharidase, but well fermented by intestinal microbes in the human large intestine and catabolised to short‐chain fatty acids and hydrogen, methane and carbon dioxide (Nakamura, Oku, & Ichinose, 2004). The prebiotic potential of cellobiose has been shown in an in vitro study using human faecal inoculum, resulting in increased bifidobacteria numbers and SCFA concentrations (Sanz, Gibson, & Rastall, 2005). Furthermore, in combination with L. rhamnosus, cellobiose was found to increase caecal numbers of lactic acid bacteria (Umeki, Oue, Mori, Mochizuki, & Sakai, 2005) as well as SCFA levels (Umeki, Oue, Mochizuki, Shirai, & Sakai, 2004) in vivo in rats. Recently, Tran, Boudry, Everaert, and Bindelle (2016) observed a stimulating effect of cellobiose on Lactobacillus populations using faeces of sows as inoculum. Thus, based on these findings, the aim of this study was to further evaluate whether cellobiose might serve as a prebiotic in the commercial nutrition of pigs (Sus scrofa domestica). Therefore, diverse concentrations of cellobiose have been tested for their effects on fermentation activity and proliferation of beneficial and potential pathogenic bacteria. Additionally, possible effects of different osmotic conditions have been considered, especially since higher osmolarity is associated with osmotic diarrhoea in vivo in pigs (Kien, Chang, Cooper, & Frankel, 2004). The application of an in vitro approach is particularly suitable for the evaluation and comparison of feed ingredients and—additives due to lower costs and animal welfare aspects.