2.4. Blood characteristics
At the beginning and the end of the 6th and 12th weeks, two pigs were randomly chosen from each pen and bled via jugular venipuncture to obtain blood samples. At each collection time, the blood samples were collected into a K3EDTA vacuum tube (Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ, USA). All blood samples were centrifuged for 30 min at 2000 ×g and 4 °C to separate the serum, after which the total proteins, IgG, white blood cell (WBC), red blood cell (RBC), lymphocyte, and albumin levels were assessed using an automatic biochemistry analyzer (HITACHI 747, Japan).