Eimeria infections in litter-based, high stocking density systems for loose-housed laying hens in Sweden

1. Coccidiosis, caused by different Eimeria species, is believed to be a mo re prominent problem in loose-housed layers kept on litter than in battery cages. In this study, the impact and development of Eimeria infections were investigated in layers kept in litter-based, high stocking density systems for loose-housed hens. 2. Layers from 57 flocks on 26 farms were followed by necropsy of a represe ntative sample of birds that died or had to be culled. Coccidiosis was diag nosed in 11 flocks (19.3%) from 9 (31%) of the farms. The outbreaks occurre d when the birds were 19 to 32 weeks old. E. maxima was identified in 6 and E. tenella in 3 of the outbreaks. 3. Sixteen of the necks were also monitored with faecal and litter samples collected at regular intervals. Oocysts were detected in samples From all t hese necks. The pattern of oocyst excretion was similar in most of the floc ks, with maximum counts at 4 to 8 weeks after introduction to the laying ho use. There was no significant correlation between the levels of oocysts in faeces and clinical coccidiosis. 4. Raising pullets without any coccidiostat, to increase their chance to de velop immunity against coccidia, was not found to decrease the risk of cocc idiosis during the production period when compared to the practice of givin g amprolium and ethopabate during the rearing period.