Trials were conducted in groups of 14 day old Ross Broiler and Lohmann Brown laying birds experimentally infected with 1,250, 5,000, 20,0000 80,000, 320,000, 1,280,000, or 5,120,000 oocysts of a field strain of
Eimeria acervulina. The oocyst output, weight gain and performance, clinical signs and mortality were recorded for 14 days post infection. Birds were also necropsied for lesion scoring and histopathological examination. Performance was related to the level of challenge. There was good correlation between clinical signs and post mortem findings with severe lesions present, extending from the duodenum to the yolk-stalk, in birds in the more heavily infected groups. The histopathological observations related to both the level of parasite challenge and the interval post infection. The infected birds showed varying degrees of villous atrophy of the duodenum and upper small intestine with hyperaemia and inflammation of the mucosa resulting in villous thickening and “clubbing”. Parasitised cells were characteristically hypertrophied and, in the heavier infections (80,000 oocysts upwards) hyperplasia of the epithelial cells was evident in the crypts.
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