2017 ACVIM Forum Research Abstract Program

Alpha diversity was significantly decreased between days À28 and 14 for cecal samples (Chao1, P = 0.043; Observed OTUs, P = 0.001; Shannon, P = 0.002) and between days 0 and 3 for fecal samples (Shannon, P = 0.021). Beta diversity, as measured by weighted Unifrac distances, showed significant differences between days À52, À28, À14, 3 and 7 in cecal and fecal samples (ANOSIM, P = 0.001). The LEfSe analysis revealed that several bacterial taxa (Christensenellaceae, Campylobacteriaceae, and Spirochaetaceae) were significantly altered due to antibiotic administration. SCFA were not significantly affected by metronidazole. Of the 553 metabolites analyzed, 223 were named and 330 were unnamed. Analysis of the named fecal metabolites found 100 that were significantly different among study days 0, 3, 7, and 14. Those metabolites that were most statistically significant (P < 0.05, q = 0.041) were active in the biosynthesis of fatty acids, steroids, proteins, carbohydrates, sucrose, and starches. Of the 223 named cecal metabolites, 93 were statistically different on study days 0, 7, and 14 (P < 0.05) but failed to remain significant after adjustment for multiple comparisons (q = 0.091). In conclusion, metronidazole administration changed the cecal and fecal microbiome and metabolome in horses.