Comparative Efficacy of Two Commercial FAdV-۴ Vaccines against Virulent Challenge in Broiler Chickens

Hepatitis–hydropericardium syndrome (HHS), caused by fowl adenovirus serotype ۴ (FAdV-۴), is a major cause of acute mortality in broiler chickens worldwide. Despite the availability of commercial vaccines, their protective efficacy under virulent challenge conditions may differ. This study aimed to compare the immunogenicity and protective efficacy of two commercial FAdV-۴ vaccines in broiler chickens. One hundred one-day-old Arian broiler chicks were randomly allocated into four experimental groups (۲۰ birds per group), with five additional contact birds per group to evaluate horizontal transmission. Birds in Groups ۳ and ۴ were vaccinated at ۲۱ days of age with commercial FAdV-۴ vaccines from Company A and Company B, respectively. At ۴۲ days of age, birds in Groups ۲, ۳, and ۴ were challenged intramuscularly with a virulent FAdV-۴ strain. Serum samples collected prior to challenge were analyzed for FAdV-۴-specific antibodies using an ELISA assay. Birds were monitored for clinical signs, mortality, and gross pathological lesions for seven days post-challenge. Before challenge, birds vaccinated with Company B developed significantly higher ELISA antibody titers (۱۴۴۰ ± SEM) than those vaccinated with Company A (۹۱۰.۵ ± SEM) and unvaccinated controls (P < ۰.۰۰۰۱). Following challenge, ۱۰۰% mortality with severe hepatic necrosis and hydropericardium was observed in the unvaccinated challenged group and in birds vaccinated with Company A. In contrast, birds vaccinated with Company B showed complete protection, with no mortality, no gross pathological lesions, and no mortality among contact birds. Commercial FAdV-۴ vaccines differed markedly in protective efficacy. Elevated ELISA antibody titers alone were not predictive of protection, emphasizing the need for rigorous evaluation and careful selection of vaccines to effectively control HHS in broiler flocks.

کلیدواژه ها:

Broiler chicken ، Commercial FAdV-۴ Vaccines ، Fowl adenovirus-۴ ، HHS ، Vaccine Efficacy