Blood samples were collected under sedation (0.01 mg/kg midazolam (Dormicum Ò , Roche Pharma AG, Reinach, Switzerland) and 10 mg/kg ketamine (Narketan Ò , Vétoquinol AG, Belp, Switzerland)) prior to challenge at week À7, À5, À3, and then weekly, starting from week 0 until week 6 p.i., later in biweekly intervals until week 20 p.i. Blood samples were obtained by jugular venipuncture using 5 mL syringes and blood was immediately transferred into EDTAtubes. 400 lL of EDTA blood was submitted for haematology analysis, 200 lL of EDTA anticoagulated whole blood were aliquoted for DNA extraction. Plasma was obtained by centrifuging approximately 2 mL of EDTA blood at 1 700· g for 10 min. Blood and plasma samples were immediately frozen at À80°C until they were processed.