Inclusion body hepatitis (IBH), caused by fowl adenovirus (FAdV) species D and E, results in significant economic losses
for the poultry industry. This study aimed to evaluate the immunogenicity of an inactivated trivalent FAdV vaccine in
SPF chickens, specifically assessing the effects of antigen payload, thimerosal addition, and booster immunization on antibody
titers. Results demonstrated a clear dose-response, with higher antigen payloads eliciting a more prolonged immune
response compared to the lowest dose. Thimerosal was confirmed to be a safe preservative, showing no negative impact
on antibody development. Furthermore, a booster immunization significantly increased antibody levels, but this effect was
observed only in the group receiving the high-payload vaccine, with peak titers at weeks 2 and 3 post-vaccination. These
findings indicate that a high-dose trivalent inactivated FAdV vaccine, administered with a booster, is highly immunogenic
and represents a promising strategy for the effective prevention and control of IBH.