الفهرس 
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Abstract
Newcastle disease virus (NDV) is still a havoc to the poultry flocks and outbreaks have occurred even in vaccinated flocks. Commercial Newcastle disease virus vaccines can provide various levels of protection against challenge with different NDV genotypes, raising the importance of the relationship between vaccines and field strains. The aim of the current work is to evaluate the effect of moisture percentage and pH on the survivability of velogenic NDV genotype VII in the poultry manure which considers a major threat to the Egyptian poultry industry since 2011 onwards. In the present study, manure from specific pathogen free (SPF) chicks was contaminated with allantoic fluid of 8 log2 NDV and kept at room temperature then daily examination of poultry manure for the survival of NDV was conducted on the basis of virus isolation and haemagglutination (HA) assay. Our results revealed that pH of the manure from time of its mixing with the NDV infected allantoic fluid till the 4th day was 7, then pH values changed progressively and recorded 8.5 till day 12. After that, pH increased towards the alkaline side and recorded pH = 9 till the 33rd day of the experiment. Regarding moisture %, after mixing the manure with allantoic fluid the moisture % of the mixture was 67%, and this wet manure remained moist (67%) till the 4th day; due to the humid environmental conditions applied at room temperature. Later, the moisture content of the treated manure decreased gradually and recorded 52.5%, 40% and 32% at the 8th, 28th and 33rd days of experiment; respectively. To recapitulate, both moisture % and pH of the poultry manure is greatly affect Newcastle disease virus survivability in the farm environment which is a critical point during cleaning and precleaning for the poultry farms to eliminate the viruses along with the use of effective disinfectants.