Allantoic Metabolites, Progesterone, and Estradiol-17β Remain Unchanged After Infection in an Experimental Model of Equine Ascending Placentitis

The objective of this study was to characterize the metabolomic profile of equine allantoic fluid in the pregnant mare with and without experimentally induced ascending placentitis with the goal of identifying biomarkers of this disease. We compared the onset of metabolomic changes with common modalities for diagnosis of ascending placentitis, including measurement of the combined thickness of the uterus and placenta (CTUP), hormonal profiling, and measurement of serum acute phase proteins. Ten pregnant pony mares were randomly divided into two groups: five healthy control mares (CONT) and five mares induced to develop ascending placentitis (PLAC) via inoculation with Streptococcus equi subsp. zooepidemicus bacteria at Days 280–285 of gestation. Allantoic fluid, whole blood, and serum were collected from both groups at 270–275 days of gestation and at the following time points postinoculation: 4 hours, Days 2, 4, 6, and 10. Differences between groups in identified metabolites, progesterone, estradiol-17β, lactate, and serum amyloid A (SAA) were assessed using an analysis of variance with repeated measures. A total of 27 metabolites were identified in allantoic fluid. No differences were detected between groups at any time point (P > .05) for any identified metabolite, progesterone, estradiol-17β, or lactate concentrations. Significant elevations in CTUP (P = .003) and SAA (P = .0001) were detected by Days 4 and 6 postinoculation, respectively. The results of this study established a database of equine allantoic fluid metabolites and confirmed the utility of uteroplacental ultrasound for detection of placentitis before the onset of hematologic changes.