Equine serum levels of sphingomyelins (SM), SM d18:1/24:0 and SM d18:1:24:2 in a pilot study (N = 6 per group) and a validation study (N = 15 per group).

Con: controls; Vacc: vaccinated; Infect: infected. *, p < 0.01. R = ratio of the ion intensity for the endogenous SM to the ion intensity of the stable isotope internal standard.