الفهرس 
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Abstract
In this work, a total of 73 commercial layer flocks in Northern Delta (Alexandria, Bohera, and Kafre-El-Sheikh governorates), which were suffering from DROP in egg production were examined for infectious etiology. Ages of these flocks at farm visit varied from 25 to 53 weeks. All flocks had a DROP in egg production ranging from 5-35% and lasted for 2-13 weeks.
Investigations included flock history, clinical signs, pathological (gross and microscopic) lesions, direct isolation and identification of etiological agent(s) or indirectly through detection of serum specific antibodies.
In these flocks, besides the quantitative DROP in egg production, qualitative changes were also observed in some flocks. The egg quality varied greatly from apparently normal to misshapen, thin-shelled eggs, irregular and rough shells, loss of pignient, or even shell-less eggs. Small-sized eggs were also observed. These changes were associated with a variety of clinical and pathological changes, which varied from mild to severe changes involving the respiratory, digestive, circulatory, urinary, reproductive or nervous systems. Eggshell abnormalities and reproductive disorders varying from inactive ovaries to egg peritonitis, oophoritis, salpingitis or ovarian tumors were all observed and recorded. The changes in one or more of the above systems were expected and attributed to the variable etiological agent(s) responsible for the DROP in egg production. These clinical and pathological changes were among the parameters helping in the recognition of the possible cause of egg DROP in the given flock. Recognition of the causative agent(s) was based on the known and described parasitological, bacteriological, virological or serological procedures
Among the recognized parasitic agents was heavy infestation with Ascaridia gaul which was the cause of egg DROP in
the 73 examined flocks (2.74%). The total DROP was 7&lO%. The mortality during the duration of egg DROP was l&2% and was mainly due to intestinal occlusion with the worms.