An experiment (complete randomised design) was conducted to investigate the effects of Laminaria hyperborea and Laminaria digitata seaweed extract inclusion on gut morphology, selected intestinal microbiota populations, volatile fatty acid concentrations and the immune status of the weaned pig. Twenty-eight piglets (24 days of age, 6.5 6 1.4 kg live weight) were assigned to one of four dietary treatments for 7 days and then sacrificed: (T1) basal diet (control); (T2) basal diet and 1.5 g/kg L. hyperborea seaweed extract; (T3) basal diet and 1.5 g/kg L. digitata seaweed extract; and (T4) basal diet and 1.5 g/kg of a combination of L. hyperborea and L. digitata seaweed extract. The seaweed extract contained both laminarin and fucoidan. Digesta samples were taken from the caecum and colon to measure the enterobacteria, bifidobacteria and lactobacilli populations and for volatile fatty acid analysis. Tissue samples were taken from the duodenum, jejunum and ileum for morphological examination. Blood samples were taken to determine the cytokine gene expression profile and to measure the phagocytotic capacity of the blood. Pigs offered diets containing L. hyperborea seaweed extract had less bifidobacteria in the colon (P , 0.05) and lactobacilli in the caecum (P , 0.05) and colon (P , 0.001). The inclusion of L. digitata seaweed extract resulted in lower populations of enterobacteria in the caecum and colon (P , 0.01), bifidobacteria in the caecum (P , 0.05), and lactobacilli in the caecum (P , 0.05) and colon (P , 0.001). Pigs offered the combination of L. hyperborea and L. digitata seaweed extracts had less enterobacteria (P , 0.05) and lactobacilli (P , 0.01) in the caecum and colon. Pigs offered the L. digitata-supplemented diet had a reduced villous height in the duodenum and jejunum (P , 0.05). The inclusion of the L. digitata seaweed extract increased the molar proportion of butyric acid in the colon (P , 0.05). There was a significant reduction in the ammonia concentration in the colon with the inclusion of L. hyperborea (P , 0.01) and L. digitata (P , 0.05) seaweed extracts. An increase in the expression of the Interleukin-8 mRNA was observed on day 6 with the supplementation of the combination of L. hyperborea and L. digitata seaweed extract (P , 0.05). The inclusion of L. hyperborea seaweed extract resulted in an increase in total monocyte number (P , 0.05). In conclusion, the supplementation of L. hyperborea and L. digitata seaweed extract alone and in combination reduced the enterobacteria, bifidobacteria and lactobacilli populations in the caecum and colon, while only marginal effects on the immune response was observed.

b-Glucans have been identified as natural biomolecules with immunomodulatory activity. The first objective of the present study was to compare the effects of purified b-glucans derived from Laminaria digitata, L. hyperborea and Saccharomyces cerevisiae on piglet performance, selected bacterial populations and intestinal volatile fatty acid (VFA) production. The second aim was to compare the gene expression profiles of the markers of pro-and anti-inflammation in both unchallenged and lipopolysaccharide (LPS)-challenged ileal and colonic tissues. b-Glucans were included at 250 mg/kg in the diets. The b-glucans derived from L. hyperborea, L. digitata and S. cerevisiae all reduced the Enterobacteriaceae population (P, 0·05) without influencing the lactobacilli and bifidobacteria populations (P.0·05) in the ileum and colon. There was a significant interaction between gastrointestinal region and b-glucan source in the expression of cytokine markers, IL-1a (P,0·001), IL-10 (P,0·05), TNF-a (P, 0·05) and IL-17A (P,0·001). b-Glucans did not stimulate any pro-or anti-inflammatory cytokine markers in the ileal epithelial cells. In contrast, the expression of a panel of pro-and anti-inflammatory cytokines (IL-1a, IL-10, TNF-a and IL-17A) was down-regulated in the colon following exposure to b-glucans from all the three sources. However, the data suggest that the soluble b-glucans derived from L. digitata may be acting via a different mechanism from the insoluble b-glucans derived from L. hyperborea and S. cerevisiae, as the VFA profile was different in the L. digitata-treated animals. There was an increase in IL-8 gene expression (P, 0·05) in the gastrointestinal tract from the animals exposed to L. digitata following an LPS ex vivo challenge that was not evident in the other two treatment groups. In conclusion, b-glucans from both seaweed and yeast sources reduce Enterobacteriaceae counts and pro-inflammatory markers in the colon, though the mechanisms of action may be different between the soluble and insoluble fibre sources.

The aim of the present study was to establish the optimum inclusion level of laminarin derived from Laminaria digitata on selected microbial populations, intestinal fermentation, cytokine and mucin gene expression in the porcine ileum and colon. A total of twentyone pigs (mean body weight 17·9 kg) were randomly assigned to one of three dietary treatments: T1 -basal (control) diet, T2 and T3 -basal diets supplemented with laminarin included at 300 and 600 parts per million (ppm), respectively. Selected intestinal bacterial populations and volatile fatty acid (VFA) concentrations were measured in the ileum and colon. Relative gene expression levels for specific cytokine and mucin genes were investigated in ileal and colonic tissue in the absence and presence of a lipopolysaccharide (LPS) challenge. There was an up-regulation of MUC2 gene expression at the 300 ppm inclusion level in the ileum. In the colon, there was a significant reduction in the enterobacteriaceae population at the 300 ppm inclusion level (P¼ 0·0421). Dietary supplementation of 600 ppm laminarin led to a significant increase in MUC2 (P¼0·0365) and MUC4 (P¼ 0·0401) expression in the colon, and in the total VFA concentration in the caecum (P¼ 0·0489). A significant increase was also recorded in IL-6 (P¼0·0289) and IL-8 gene expression (P¼0·0245) in LPS-challenged colonic tissue at both laminarin inclusion levels. In conclusion, dietary inclusion of 300 ppm laminarin appears to be the optimum dose in the present study due to the reduction in the enterobacteriaceae populations and enhanced IL-6 and IL-8 cytokine expression in response to an ex vivo LPS challenge.

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