Variable importance in projection (VIP) scores of serum metabolites in sows during pregnancy and after farrowing in the control and NCG groups. (A) VIP scores of serum metabolites in sows on D30 of pregnancy. (B) VIP scores on D70. (C) VIP on D110. (D) VIP scores after farrowing. C30, C70, C110, and CF represent control group at D30 of pregnancy, D70 of pregnancy, D110 of pregnancy, and after farrowing, respectively; N30, N70, N110, and NF represent NCG group at D30 of pregnancy, D70 of pregnancy, D110 of pregnancy, and after farrowing, respectively; Red represents a higher expression abundance of metabolite, while blue represents lower; ***: the expression abundance of metabolite was significantly different between NCG group and control group (p < 0.001); **: p < 0.01; *: p < 0.05; n = 8.