The consumption of dietary fiber has been shown to regulate systemic and intestinal inflammation. An inverse relationship between fiber intake and circulating acute-phase proteins has been observed in humans (Basu et al., 2006; Ma et al., 2006). Mechanistically, dietary fiber may alter the inflammatory response through regulating the expression of cytokines. Indeed, recent studies have shown that supplementing pig diets with a combination of 4 sources of dietary fiber increased colonic IL-6 expression (Pie et al., 2007). To date, there are no published data on the effects of different fiber types on the expression of cytokines or whether feeding fiber alters markers of systemic inflammation in pigs. Inflammation via the action of cytokines has been found to regulate pathways involved in protein synthesis. Endotoxin challenge decreases the activation of S6 kinase (S6K1), a protein involved in protein translation initiation (Ruvinsky and Meyuhas, 2006) in skeletal muscle (Kimball et al., 2003; Lang and Frost, 2004). However, piglets infected with rotavirus enteritis have an increased level of activated S6K1 in intestinal tissue (Rhoads et al., 2007). There is little data available exploring the effect of dietary fiber on cytokine expression and subsequent effects on anabolic pathways and piglet growth. Therefore, the objectives of this study were to determine the effects of different types of dietary fiber on pig growth, intestinal cytokine expression, and markers of systemic inflammation. Intestinal tissue DNA and protein content and the activation of intestinal S6K1 were also determined. Pigs (n = 120; initially 5.2 kg and 24 d of age) were randomly assigned to diets containing 1 of 4 fiber sources: 1) control diets containing no added fiber source, 2) diets containing 7.5% distillers dried grains with solubles (DDGS), 3) diets containing 7.5% soybean hulls, or 4) diets containing 7.5% citrus pulp. The experimental diets were fed for 4 wk in 2 phases (phase 1, wk 1 and 2; phase 2, wk 3 and 4). Intestinal tissue samples, liver samples, and blood samples were collected from a subset (n = 24; 6 pigs/treatment) of the pigs on day 7, and blood samples were collected from another subset (n = 24; 6 pigs/ treatment) of pigs on day 28 of the experiment. Dietary treatment had no effect on ADG, ADFI, or G:F throughout the experiment. Likewise, pig BW variability (CV), plasma IGF-I, or the plasma concentration of the acute phase proteins, á1-acid glycoprotein, C-reactive protein, and haptoglobin, were not affected by dietary treatment. Real-time RT-PCR analysis revealed that on d 7, pigs fed DDGS had a greater (P < 0.05) relative abundance of the mRNA encoding IL-6, IL-1â, and IL-10 in ileum tissue than pigs fed all other diets. Diets containing DDGS had no effect on the relative abundance of tumor necrosis factor á or interferon-ã mRNA in ileum tissue on d 7. The d-7 mRNA expression of cytokines was not altered in jejunum, colon, or liver tissue by dietary treatment. Intestinal tissue protein content or jejunum and ileum DNA concentrations were not affected by diet. Western blot analysis found no effect of dietary treatment on the activation of S6 kinase in jejunum, ileum, or colon tissue on day 7. These results indicate that feeding 7.5% of a fiber source as DDGS, soybean hulls, or citrus pulp does not affect growth performance or circulating markers of inflammation in weanling pigs and that feeding DDGS increases the expression of both pro inflammatory and anti-inflammatory cytokines in intestinal tissue.