Eimeria: further studies on the immunisation of young chickens kept in litter pens

Chickens were inoculated with small numbers of oocysts of attenuated (E. tenella TA and E. mivati MA) and virulent strains of E. acervulina, E. brunetti, E. maxima and E. necatrix under conditions designed to permit reinfection. Chickens were immune to challenge with pathogenic laboratory strains 6 weeks after inoculation with either the homologous strains or attenuated derivatives. Immunity to challenge with heterologous strains was also achieved, except that it was incomplete with E. maxima. To obtain complete protection against heterologous challenge with E. maxima, it was necessary to immunise with several strains. Chickens immunised at 1 or 2 weeks of age showed a stronger immunity than birds immunised at 1 day old when challenged at 6 weeks of age. The effect of inoculating chickens with 0.1-10 times a standard immunising dose was examined. Chickens given 0.1-1 times the standard dose were substantially immunised but body weight gain was reduced with higher doses. The results show that controlled immunisation of 1- or 2-week-old chickens against six species of Eimeria is possible, and that a substantial degree of immunity develops within 2 weeks of exposure. This immunity was effective for at least 18 weeks.