Effect of dietary inorganic sulfur level on growth performance, fecal composition, and measures of inflammation and sulfate-reducing bacteria in the intestine of growing pigs

Two experiments investigated the im- pact of dietary inorganic S on growth performance, intestinal inflammation, fecal composition, and the presence of sulfate-reducing bacteria (SRB). In Exp. 1, individually housed pigs (n = 42; 13.8 kg) were fed diets containing 2,300 or 2,100 mg/kg of S for 24 d. Decreasing dietary S had no effect on ADG, ADFI, or G:F. In Exp. 2, pigs (n = 64; 13.3 kg) were fed diets containing 0, 0.625, 1.25, 2.5, or 5.0% CaSO4, there- by increasing dietary S from 2,900 to 12,100 mg/kg. Two additional diets were fed to confirm the lack of an impact due to feeding low dietary S on pig per- formance and to determine if the increased Ca and P content in the diets containing CaSO4 had an impact on growth performance. Pigs were fed for 35 d. Ileal tissue, ileal mucosa, and colon tissue were harvested from pigs fed the 0 and 5% CaSO4 diets (low-S and high-S, respectively) to determine the impact of dietary S on inflammation-related mRNA, activity of mucosal alkaline phosphatase and sucrase, and pathways of in- flammatory activation. Real-time PCR was used to quantify SRB in ileal and colon digesta samples and feces. Fecal pH, sulfide, and ammonia concentrations were also determined. There was no impact on growth performance in pigs fed the diet reduced in dietary S or by the increase of dietary Ca and P. Increasing dietary S from 2,900 to 12,100 mg/kg had a linear (P < 0.01) effect on ADG and a cubic effect (P < 0.05) on ADFI and G:F. Real-time reverse-transcription PCR analysis revealed that pigs fed high-S increased (P < 0.05) the relative abundance of intracellular adhesion molecule-1, tumor necrosis factor-α, and suppressor of cytokine sig- naling-3 mRNA, and tended (P = 0.09) to increase the relative abundance of IL-6 mRNA in ileal tissue. Likewise, pigs fed high-S had reduced (P < 0.05) abun- dance of nuclear factor of κ light polypeptide gene en- hancer in B-cells inhibitor-α and increased (P < 0.05) phospho-p44/p42 mitogen-activated protein kinase in ileal tissue, but there was no effect of dietary S on mu- cosal alkaline phosphatase or sucrase activity. Pigs fed the high-S diet had decreased (P < 0.05) total bacteria in ileal digesta, but increased (P < 0.05) prevalence of SRB in colon contents. Fecal sulfide was increased (P < 0.05) and fecal pH was deceased (P < 0.05) in pigs fed high-S. The data indicate that growing pigs can toler- ate relatively high amounts of dietary inorganic S, but high dietary S content alters inflammatory mediators and intestinal bacteria.