Blood samples were collected into vacuum tubes containing
heparin at 28 days of age. The samples
were stored at 4°C and transported to the laboratory
within 24 h after collection. The blood samples were
used to quantify the concentration of plasma IgG and
identify the number of leukocyte subsets. Plasma samples
were recovered by centrifuging the blood at 800 × g
for 10 min at 4°C and frozen at 30°C until use.