In the current study, colonic contents were analyzed from a previous randomized complete block experiment where one hundred 4-week-old pigs were divided into five inoculum groups (negative control, Brachyspira intermedia, Brachyspira pilosicoli, B. hyodysenteriae or “B. hampsonii”) and fed one of two diets containing no (diet 1) or 30% (diet 2) DDGS. Colonic contents were collected at necropsy either 72 hours after the development of SD or at 21 days post-inoculation in control pigs and those not developing SD, and were flash frozen in liquid nitrogen and retained for the analyses described in this report. Pigs receiving diet 2 and inoculated with either B.hyodysenteriae or “B. hampsonii” developed SD nearly twice as fast as pigs receiving diet 1. The colonic microbiome in each necropsy sample was analyzed using 16S rRNA profiling and compared for differences in richness and diversity of bacterial species. In the non-inoculated control pigs, no difference in richness (alpha diversity) was observed; however, a significant difference was observed in the beta diversity between groups (P < 0.0001) with a dramatic shift in the Bacteroidetes:Firmicutes ratio where higher ratios were observed in those pigs fed DDGS (diet 2). For pigs that developed SD, there was a significant difference in richness relative to those that did not regardless of diet with fewer total species observed in SD pigs (P = 0.001). The beta diversity was also significantly different between pigs with SD and those without where SD pigs had lower Bacteroidetes:Firmicutes ratios on average and a marked increase in relative abundance of Proteobacteria. The relative abundance of Spirochaetes was higher in pigs fed DDGS relative to pigs fed the control diet. Further investigation is warranted to better determine the specific bacterial species underlying these shifts in the colonic microbiome and the relationship of these bacteria with strongly beta-hemolytic Brachyspira spp. as pigs fed DDGS appear at increased risk for developing SD.
Eric Burrough
Iowa State University Veterinary Diagnostic Laboratory
1600 South 16th St, Ames, IA 50011
[email protected]