Metabolomics Uncovers Serum Biomarkers That Can Predict the Risk of Retained Placenta in Transition Dairy Cows

A combination of direct injection and tandem mass spectrometry with a reverse-phase liquid chromatography and tandem mass spectrometry (DI/LC-MS/MS) was used to detect serum metabolite signatures in 20 cows that expelled their fetal membranes normally and 6 cows that retained placenta. We aimed to identify serum biomarkers that can predict the risk of retained placenta (RP) in transition dairy cows. Blood samples were obtained from the coccygeal vein once per week at 0700 before the morning feeding at -8 and -4 weeks before parturition, at the week of RP, and at +4 and +8 weeks postpartum. We studied perturbation of serum metabolites using AbsoluteIDQ 180 kit (BIOCRATES Life Science AG, Innsbruck, Austria) which contained metabolites related to amino acids (AAs), acylcarnitines, biogenic amines, glycerophospholipids, sphingolipids, and hexose. Univariate analysis of data was performed using Wilcoxon-Mann-Whitney test provided by R (Version 3.0.3, 2008). Metabolomic data were analyzed using the MetaboAnalyst software. Statistical significance was declared at P<0.05. Results showed that cows with RP were characterized by a decrease in LysoPC a C18:2, C20:3, C20:4, C28:0 and C28:1 at -8 weeks before parturition and during the week of diagnosis of RP (P<0.01). At -4 weeks prior to calving LysoPC a C20:4 and C28:0 were decreased. Concentrations of phosphatidylcholines (PCs) changed after calving with 12 and 4 species of PCs elevated at +4 weeks and +8 weeks after calving, respectively (P<0.05). Cows with RP were characterized by increased concentrations of sphingomyelins (SMs) in the serum at -8 weeks prior to parturition (P<0.05), the week of RP (P<0.05) and at +4 and +8 weeks after parturition (P<0.05). Amino acids Lys, Ile, and Leu were greater in cows diagnosed with RP during all experimental time. Biogenic amines, acetylornithine, asymmetric dimethylarginine, total dimethylarginine, carnosine, creatinine, and sarcosine were greater in RP cows during diagnosis week (P<0.01). It is intriguing that pre-RP, RP, and post-RP cows showed an increased concentration of Lys, Ile, Leu, and acetylornithine during all experimental time points studied (P<0.01). Moreover, LysoPC a C20:4 and C28:0, Orn, and Asn decreased before parturition and at the disease diagnosis week (P<0.05). In conclusion RP is preceded and associated with alterations in multiple species of ACs, PCs, LPCs, AAs, and BAs starting from -8 weeks prior to parturition. Alterations of serum Lys, Orn, acetylornithine, LysoPC a C28:0, Asp, Leu, and Ile might be novel serum biomarkers for prediction of risk of RP in dairy cows.