Acquisition of immunity to Eimeria maxima in newly hatched chickens reared on new or reused litter.

The acquisition of immunity by chickens infected 18 h post-hatch with 100 oocysts of Eimeria maxima and reared in floor-pens in contact with their droppings was investigated. In the first experiment, birds were placed on new litter and immunity was measured at 2, 3, 4, and 5 weeks by calculation of weight gain from days 0 to 7 following challenge with 100000 oocysts or by oocyst production in the faeces from days 5 to 8 following challenge with 500 oocysts. In the second experiment, birds were placed on new litter or reused litter from the first experiment (1 week after birds from the first experiment had been removed when 6 weeks of age), and were challenged at 1, 2, and 3 weeks of age. In the first experiment, immunity had developed in birds challenged at 3, 4, and 5 weeks, judged by weight gain and oocyst production, but immunity was not complete at 2 weeks. In the second experiment, immunity had developed in birds challenged at 1, 2, and 3 weeks measured by either criterion. In both experiments, birds produced small numbers of oocysts in their faeces following challenge. Judged by the weight gain following challenge, no significant difference in the acquisition of immunity was observed whether birds were reared on new or reused litter.