Table 4.
Equation of linear regressions detected by standard samples via GC-MS.
| SCFA | Equation | R 2 | Linearity range (mg/L) |
|---|---|---|---|
| Acetic acid | y = 10.001982 * x − 3.631493 | 0.998242 | 0.1–20 |
| Propionic acid | y = 4.991172 * x − 1.707163 | 0.995486 | 0.1–9.5 |
| Isobutyric acid | y = 9.838497 * x − 1.317041 | 0.998669 | 0.1–8 |
| Butyric acid | y = 69.122314 * x-21.545157 | 0.997229 | 0.1–20 |
| Isovaleric acid | y = 72.284002 * x − 14.156633 | 0.998779 | 0.1–20 |
| Valeric acid | y = 43.669973 * x − 11.692827 | 0.998961 | 0.1–20 |
| Caproic acid | y = 34.683801 * x − 7.396451 | 0.994521 | 0.1–8 |
A significant difference of the seven SCFA except valeric acid was found between normal and diarrheal yaks. Acetic acid, propionic acid, butyric acid, isobutyric acid, and caproic acid were found in normal yaks, significantly higher than diarrheal yaks (p-value <0.01). Isovaleric acid in normal yaks was also significantly higher than diarrhea yaks (p-value <0.05) ( Figure 9 ).