All intradermal administrations were performed using
a 31G insulin syringe (Ultra-Fine II insulin syringe,
Becton Dickinson and Co.). We selected 3 skin parts
that have less feather than other parts to compare the
immune response by different skin injection site. 50 μL
108.3 EID50 vaccine was delivered intradermally through
the left pectoral skin, left flank skin, and left interdigital
web skin at 6-week-old ducks. All ducks were bled
for serological examination 1, 2, and 3 wk after vaccination