The Influence of Maternally Derived Antibodies on the Efficacy of a Live Attenuated aMPV/B Vaccine Strain 1062 by Spray or Drinking Water Vaccination in Broilers in Laboratory and Field Conditions

Avian metapneumovirus (aMPV) is a highly contagious upper respiratory infection in poultry worldwide. Maternally derived antibodies (MDAs) do not directly protect against aMPV infection. This study assessed the interference of MDAs on the efficacy of a commercial live attenuated aMPV subtype B vaccine, strain 1062, in broilers, focusing on its impact on ciliary activity. Using two vaccination routes (coarse spray and drinking water), both laboratory and field tests were conducted. The results demonstrated that the vaccine significantly reduced ciliostasis after challenge, with a maximum of 25% of affected chicks in vaccinated groups compared to a minimum of 87.5% in control groups. Additionally, vaccinated groups showed less tracheal damage, with fewer than two rings affected on average, compared to more than five rings in control groups. Both spray and drinking water methods provided similar protection against clinical signs of infection. Additionally, MDAs did not interfere with vaccine effectiveness, as both MDA+ and MDA- chicks showed comparable immune responses and protection. Serological tests confirmed that vaccinated birds developed elevated levels of antibodies after challenge. Overall, the vaccine was found to be effective in preventing the detrimental effect of aMPV on ciliary activity that could lead to respiratory problems in broilers, providing immunity 3 wk postinfection and offering flexible vaccination options. These findings support the vaccine's use in commercial poultry farms, even in the presence of MDAs.