Neospora caninum-specific IgG responses after inoculation with the Nc-Spain7 isolate. IgG response in the serum of heifers intravenously challenged with 107 (IV1), 105 (IV2), 103 (IV3), and 102 (IV4) tachyzoites and the uninfected control group (A), and intravenously and subcutaneously challenged heifers with 105 Nc-Spain7 tachyzoites and the uninfected control group (B). Total IgG antibodies are expressed as a relative index percent (RIPC). RIPC value for each sample was estimated according to the following formula from corresponding optical densitity (OD) values: RIPC = [(OD sample − OD405 negative control)/(OD405 positive control − OD405 negative control)] × 100. Each point represents the mean + SEM (Standard error of mean) at the different sampling times until the endpoint for each group. Note that the IV1 group had a peak of IgG levels by 3 wpi compared to its basal pre-infection levels (P < 0.0001), and the IV2 group had a significant increase in IgG levels 1 week later (4 wpi) (P < 0.05) (A). Note the delayed increase in IgG levels with respect to basal pre-infection levels for the SC group compared to the IV2 group (P < 0.001) (B). ****P < 0.0001, ***P < 0.001 and *P < 0.05.