#13-212

Complete

Date Full Report Received

02/23/2015

Date Abstract Report Received

02/23/2015

Investigation

Institution:
Primary Investigator:

The diversion of an increasing portion of the U.S. corn crop to ethanol production has resulted in increased feed costs for pork producers. To mitigate this trend, many pork producers have increased their use of ethanol byproducts in commercial diets including increased feeding of distiller’s dried grains with solubles (DDGS). The inclusion of DDGS raises the insoluble fiber in the ration and the impact of this diet change on the colonic flora can be considerable. The large intestine contains a dynamic microenvironment with tremendous interplay between microorganisms. Any alteration to the physical or chemical properties of the colonic contents has the potential to impact the resident bacterial population and potentially favor or inhibit the establishment of pathogenic species. Previous work has shown that the development of swine dysentery (SD) in gnotobiotic pigs is dependent upon the presence of one or more additional anaerobic bacteria concurrent with Brachyspira hyodysenteriae, yet it is unknown if these specific anaerobic species are more prevalent in the microbiota of pigs that develop SD naturally versus those that do not, or in those pigs that are fed diets containing increased insoluble fiber sources such as DDGS.

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.

Contact information:
Eric Burrough
Iowa State University Veterinary Diagnostic Laboratory
1600 South 16th St, Ames, IA 50011
burrough@iastate.edu