IgG humoral immune responses. Serum levels of total IgG (a), IgG1 (b) and IgG2 (c) antibodies against N. caninum. Immunoglobulin levels are expressed as a relative index percent (RIPC) according to formula: RIPC = (OD405nm sample - OD405nm negative control)/(OD405nm positive control - OD405nm negative control) × 100. Each point represents the mean + SD at the different sampling times. (*) Indicates significant differences (P < 0.05) between the two infected groups (G1 and G2). Data for 49 dpi are not represented because only one heifer from G1 and two heifers from G2 maintained pregnancy.