Transgenic Neospora caninum strains constitutively expressing the bradyzoite NcSAG4 protein proved to be safe and conferred significant levels of protection against vertical transmission when used as live vaccines in mice

► We use the Nc-1 SAG4c1.1 and Nc-1 SAG4c2.1 transgenic strains as live vaccines. ► Nc-1 SAG4c1.1 offers less protection than Nc-1 SAG4c2.1 or their ancestor (Nc-1 WT). ► Nc-1 SAG4c2.1 strain is the best candidate in terms of safety and protection. ► Transgenic strains are a good approach for developing marked live vaccines.