Selected ion monitoring chromatograms (A, D, H) and MRM scan chromatograms (B, C, E–G, I–K) of BAs from co-injection of female piglet urine extract and standards. S1–S34 are BA standards. S1, ωMCA; S2, αMCA; S3, βMCA; S4, γMCA; S5, CA; S6, T-αMCA; S7, T-βMCA; S8, T-γMCA; S9, T-CA; S10, G-γMCA; S11, G-CA; S12, MDCA; S13, UDCA; S14, HDCA; S15, isoDCA; S16, CDCA; S17, DCA; S18, 3-DCA; S19, T-UDCA; S20, HDCA; S21, T-CDCA; S22, T-DCA; S23, G-UDCA; S24, G-HDCA; S25, G-CDCA; S26, G-DCA; S27, UDCA-3S; S28, CDCA-3S; S29, alloLCA; S30, isoLCA; S31, LCA; S32, T-LCA; S33, G-LCA; S34, G-LCA-3S.