In vitro fermentation of substrates from Saccharina latissima by broiler chicken’s caecal microbiota

This study investigated seasonal variations in the composition of the kelp species Saccharina latissima cultivated on the Swedish west coast and, using an in vitro fermentation system, evaluated the effect of fermented whole S. latissima biomass or biomass components on the gut microbiota of broiler chickens. Caecal contents of six Ross 308 broilers fed a standard wheat and soy-based diet were retrieved on two different occasions, with three birds sampled per occasion. Two in vitro fermentation batches (A, B) were established using caecal contents as inoculum, and whole S. latissima, ethanol-washed S. latissima, laminarin extract or inulin (control) as substrate. Total short-chain fatty acid (SCFA) content, gas production, pH and changes in microbiota composition were studied after 6, 12 and 24 h of fermentation. Analysis of seasonal variations revealed that S. latissima harvested in June had the highest laminarin content and lowest ash and crude protein content. Broiler microbiota, SCFA profile, gas production and pH mainly varied depending on fermentation inoculum, but there were also some variations depending on substrate. For instance, uncultured bacterium from Clostridiales _vadinBB60_group showed higher relative abundance (RA) in batch A, while Faecalibacterium showed higher RA in batch B. Whole and ethanol-washed S. latissima resulted in highest RA of unclassified Ruminococcaceae and Tyzzerella for both batches, while ethanol-washed S. latissima and laminarin gave highest RA of Erysipelatoclostridium. Inulin resulted in highest RA for the genus Subdoligranulum. Acetic, n-butyric and propionic acid were the main fermentation products and total SCFA level was higher in batch B. Within batch B, inulin and laminarin generated higher levels of acetic and butyric acid. When using inulin and laminarin, gas production was lower in batch B compared with batch A. In summary, this study showed that S. latissima is a good source of laminarin, especially when harvested in summer. Within the in vitro system, the microbiota was affected by different substrates, but inoculum source was identified as an important contributor to microbial community development during fermentation.