Protection of the reproductive tract of young chicks by Newcastle disease virus-induced haemagglutinationinhibition antibodies.

The present study was conducted to assess the haemagglutination-inhibition (HI) titres required to protect the chicken reproductive tract against direct damage caused by Newcastle disease virus (NDV). Precociously induced oviduct and uterus by oestrogen treatment of young chicks were used to assess the damage or protection against the damage by analysis of ciliostasis or histopathological lesions. Unvaccinated day-old female white leghorn chickens were used as the maternally derived antibody (MDA) group. Chickens were vaccinated with either a live lentogenic vaccine on day 14 of age or, along with it, an inactivated vaccine at day 36 of age, to generate birds with a range of primary or secondary response induced HI antibodies. Birds with different HI antibody levels were challenged with virulent NDV. It was found that a HI antibody titre of 128 and above was protective against direct damage of the reproductive tract, while the 32-64 titre range was protective when derived through secondary vaccination only.