Minnesota is the leading state in number of turkeys produced in the US. Turkey flocks in the field are usually vaccinated several times using live avian orthoavulavirus 1 (AOAV-1) vaccines starting as early as 2 weeks of age (WOA). During the years 2018-2019, many turkey flocks were diagnosed with low virulence AOAV-1 infection around 9 WOA that lead to respiratory disease although they were previously vaccinated. This study was designed to investigate the immunity against AOAV-1 in Minnesota turkey flocks in the field and experimentally after vaccination. We reviewed antibody titers against AOAV-1 from turkey flocks tested by ELISA at Minnesota Poultry Testing Laboratory (n=1292). Up to 9 WOA, more than 85% of the field flocks tested had unprotective antibody titers against AOAV-1. However, experimentally vaccinated commercial poults at 3 WOA by eye drop method had an ELISA GMT of 6011 at 7 WOA. Oropharyngeal virus shedding after vaccination was 10, 70, 80, & 40% at 1, 3, 5, & 7 days post vaccination. This study demonstrates that experimentally vaccinated turkeys respond very well to AOAV-1 vaccine when properly administered. However, there is clear vaccination failure in the field. Vaccine application in the field is commonly administered in drinking water and this method is more susceptible to failure due to many variables in this procedure. We recommend to choose the most effective method of vaccine administration. Given the high incidence of inadequate immunity induced in commercial turkeys upon mass application of live AOAV-1 vaccines in water, alternate application methods and subsequent monitoring of the serological antibody response must be undertaken to ensure a proper immune response.

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