SUMMARYIn a survey of chicken coccidia in France during 1994, samples of litter were collected from 41 farms. On 31 of these farms, eimerian oocysts were abundant enough to allow monitoring of their numbers in the litter. Peak total oocyst counts on these farms ranged from 16,200 to 1,254,000/g of litter, but no coccidiosis was observed. The chickens reared without anticoccidial agents in their food (poulets biologiques) produced higher and earlier peak oocyst counts in litter than the chickens given medicated food (poulets labels). The oocysts in litter samples from 22 farms (13 poulet biologique, five poulet label, two standard broiler, one breeder and one layer) of the original 41 were identified. Six of the seven eimerian species known to parasitize chickens were found, using combinations of five methods (oocyst morphology, intestinal lesions, enzyme electrophoresis, growth in embryonating eggs and prepatent time). Multispecific infections predominated (95% of 22 farms), up to six species occurring together. Of farms where oocysts were detected, the percentages with each species were: Eimeria acervulina (100%), E. mitis (82%), E. tenella (77%), E. maxima (73%), E. praecox (45%) and E. brunetti (27%). These appear to be the first definite records of E. mitis and E. praecox for France. Although E. necatrix was not found in this survey, it had recently been detected by other workers in France, so that all seven chicken Eimeria species were known to be contemporaneous.

Losses caused by coccidiosis are a significant problem in the rearing of breeder and layer flocks. A live vaccine has been developed that contains attenuated lines of the seven species of Eimeria that infect the chicken. The attenuated lines were derived from virulent strains by selection for earlier development in chickens. In 11 field trials, the performance of vaccinated chicks was compared with that of matched controls receiving conventional drug prophylaxis. The vaccine was given in the drinking water to 116,600 young chickens and provided excellent control of coccidiosis. The occurrence of coccidial oocysts in the litter, coccidial lesions post mortem and overt coccidiosis was markedly lower in the vaccinated birds than in the controls.

Broiler breeder hens from the same hatch were reared as two separate flocks, one in the field and one in experimental accommodation. Both received the same vaccination programme using the same batches of vaccines. One flock showed serological evidence of infection with chicken anaemia agent starting at 8 weeks, the other starting at 22 weeks old. Newcastle disease mean antibody titres 4 weeks after killed vaccine injected at 18 or 19 weeks old were 4.6 logs lower in the flock showing chicken anaemia agent antibody from 8 weeks old than in the flock seroconverting at 22 weeks. Three other field flocks showing poor responses to killed Newcastle disease vaccines were examined and found to be chicken anaemia agent positive when vaccinated: a further three flocks showing good Newcastle disease antibody responses were shown to be chicken anaemia agent-antibody negative. No difference in response to infectious bronchitis or infectious bursal disease killed vaccines was demonstrable between the two trial flocks. The significance of chicken anaemia agent as a potential immunosuppressive agent for chickens is discussed with special reference to the control of Newcastle disease in laying and breeding hens.

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