Development of a precocious strain of Eimeria tenella

Abstract

Studies on the prevalence of caecal coccidiosis in

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chicken,

by referring to the postmortem registers

maintained at the centre of Excellence in Pathology, College of Veterinary and Animal Sciences~ Mannuthy revealed that 48.4 per cent of 550 coccidia positive

viscera was due to Eimeria tenella. A pure line of E. tenella was established in the laboratory by single oocyst isolation technique from a virulent field case of caecal coccidiosis in chicken. A stabilised strain of E. tenella was developed by administering a dose of 1.5x103 sporulated pure line E. tenella oocysts per bird orally to six three to five day old coccidia free White Leghorn chicks and harvesting the caecal contents at 168 hr pi for 15 cyclic~l passages. For the development of a precocious strain of E. tenella a dose of 1.5x103 sporulated E. tenella oocysts per bird was administered orally to six, three to five day old White Leghorn chicks. The caecal contents were harvested at 136 hr pi and the oocysts were allowed to sporulate and subsequently repassaged by applying selection pressure in increments of one hour reduction at each passage. At the end of 18 cyclical passages, oocysts obtained at 125 hr pi were designated E. tenella. as the precocious strain of A comparative study between the precocious and stabilised strain of E. tenella revealed the following observations~ The prepatent period of the precocious strain was 125 hr while that of the stabilised strain was 135 hr. The oocyst morphology did not reveal any significant difference between the two strains. The precocious strain was less pathogenic and produced milder clinical signs than the stabilised strain. The gross lesions of caeca were less morbid in the precocious strain infected group. Weight gain was more in the precocious strain infected group than in the stabilised strain infected group. The precocious strain produced less mortality and showed a drop in oocyst production. Endogenous study revealed an accelerated growth in the early stages of the asexual life cycle in the precocious strain infected group