Differences in plasma and uterine metabolome associated with vaginal discharge characteristics in peripartum dairy cows

The objective of this study was to characterize differences in plasma and uterine metabolome from transition dairy cows according to vaginal discharge (VD) characteristics observed postpartum. Plasma samples were collected at 3 time points: prepartum (-14 d relative to calving; PP), on the day of calving (D0), and the day of diagnosis of metritis (Dx), whereas the uterine lavage samples were collected at D0 and Dx. The VD was assessed on a 5-point scale as follows: 1 = not fetid, normal lochia, viscous, clear, red, or brown; 2 = cloudy, pink, red, or brown mucoid discharge with flecks of pus; 3 = not fetid, pink, red, or brown mucopurulent discharge with <50% pus; 4 = not fetid, pink, red, or brown purulent discharge with ≥50% pus; 5 = fetid, watery, red-brown discharge. The plasma and uterine samples were analyzed via untargeted metabolomics using GC time-of-flight MS. The resulting data were analyzed using partial least squares-discriminant analysis and permutational multivariate ANOVA, and t-tests. The analyses showed no difference between VD groups in plasma at PP, and plasma or uterus at D0. At Dx, the plasma metabolome differed between VD5 and VD1, VD2, and VD3, but was similar to VD4. No differences in plasma metabolome at Dx between VD1, VD2, VD3, and VD4 were observed. The uterine metabolome at Dx differed between VD5 and VD1, VD2, VD3, and VD4. Our findings indicate that cows with fetid, watery, red-brown VD and cows with purulent VD present similar systemic (plasma) metabolic alterations compared with cows with clear or mucopurulent VD. However, local (uterine) metabolic alterations are limited to cows with fetid, watery, red-brown VD only.