Bwala , D., Fasina, F., Wyk, A. V., & Duncan, N. (2011). Effects of Vaccination with Lentogenic Vaccine and Challenge with Virulent Newcastle Disease Virus (NDV) on Egg Production in Commercial and SPF Chickens. International Journal of Poultry Science, 10(2), 98–105. https://doi.org/10.3923/ijps.2011.98.105