Anti-Neospora caninum serum IgG measured by ELISA in non-infected and non-medicated negative control calves (c), infected and non-medicated positive control calves (I_w/oT), infected and one-day medicated calves (I_1T) and infected and six-day medicated calves (I_6T). Number of animals per group as in Table 1. AU = antibody units; dotted line (cut-off) indicates the negative/positive threshold determined by the mean plus 3 S.D. of measurements from non-infected control calves. Error bars display standard deviations.