Testudinid herpesviruses (TeHVs) and ranaviruses are important pathogens of tortoises, but no treatments are available. Lysine may inhibit herpesvirus (HV) replication, although its effectivity has been questioned. Lactoferrin has antiviral activity against a range of viruses by inhibiting adsorption to cells. Media were supplemented with 6.25–10 mg/ml lysine and 0.625–1 mg/ml lactoferrin, individually or combined, and the effects measured against the replication of TeHV-1, TeHV-3, or a ranavirus in Terrapene heart cells (TH-1). Cytotoxicity testing was also carried out with the same concentrations. Lysine alone inhibited cell growth after 24 and 48 h, whereas lactoferrin only reduced cell growth after 24 h. TeHV-1 titers were only reduced by the addition of a combination of 10 mg/ml lysine and 1 mg/ml lactoferrin after 48 h (43.8% reduction) and by 10 mg/ml lysine (82.2% reduction). The same concentration of the combined substances led to an average reduction in TeHV-3 titers of 43.8% after 24 h and 68.4% after 48 h, respectively, while 10 mg/ml lysine led to an average reduction of 92.5% after 48 h. Lactoferrin alone did not reduce HV titers. Both concentrations of the combined substances led to titer reductions of the ranavirus (86.7–96.8%), and testing of the individual substances led to a reduction of 97.6% after 48 h with 10 mg/ml lysine and of 82.2% after 24 h with 1 mg/ml lactoferrin.