Blastocystis spp. Positivity Is Associated with Altered Fecal Bacterial Communities and Reduced Short-Chain Fatty Acid Concentrations in Diarrheic Yaks

Yaks (Bos grunniens) are important livestock on the Qinghai–Tibetan Plateau, but the relationship between Blastocystis positivity, fecal bacterial communities, and microbial metabolites remains unclear. This cross-sectional study compared fecal bacterial profiles and short-chain fatty acid (SCFA) concentrations in six Blastocystis-positive and six Blastocystis-negative diarrheic yaks from Lhasa, Tibet Autonomous Region, China. Bacterial communities were characterized by 16S rRNA gene amplicon sequencing, and fecal SCFAs were quantified by gas chromatography–mass spectrometry. Compared with negative yaks, positive yaks had lower concentrations of acetic acid (p < 0.01), propionic acid (p < 0.01), butyric acid (p = 0.000381), valeric acid (p < 0.01), caproic acid (p = 0.00359), and isobutyric acid (p < 0.01), whereas isovaleric acid did not differ between groups (p = 0.310). A total of 2,751,028 raw sequences were generated, of which 2,620,949 passed quality filtering. ACE (p = 0.0068), Chao1 (p = 0.0071), Faith’s phylogenetic diversity (p = 0.0019), observed ASVs (p = 0.0064), Pielou’s evenness (p = 0.011), Shannon diversity (p = 0.008), and Simpson diversity (p = 0.037) were lower in positive yaks. The groups also differed in bacterial community composition, and several taxa previously associated with fiber degradation or SCFA formation had lower relative abundances in positive yaks. PICRUSt2 indicated differences in predicted microbial functional potential. These findings indicate that Blastocystis positivity was associated with altered fecal bacterial communities and reduced concentrations of several SCFAs in diarrheic yaks. Because of the small sample size, cross-sectional design, and potential confounding by diarrhea and other unmeasured factors, causal relationships cannot be established.