Blood collection procedure
After cleansing of the haired skin surface with 70% isopropyl alcohol, 20 mL of blood was collected through an 18 g vacutainer needle directly into a red topped tube via jugular venipuncture. Blood collection was performed on days 0 (baseline), 14, 30, 90, and 180 after vaccination. A subset of horses also had blood collected on either or both days 270 and 360 after vaccination. Blood samples were stored at 4oC immediately after collection for less than 48 hours prior to be being centrifuged at 2200-2500 RPM for 15 minutes. Serum was removed and frozen at -18oC for a maximum of 14 days. Serum was thawed at 4oC for 24 hours, after which it was aliquoted into 2 mL plastic collection tubes and stored at -80oC. Serum samples were batched for testing and were only thawed once on the morning of testing to avoid freeze thaw degradation, thus maintaining protein integrity for testing.