The effect of stress on the response of chickens to coccidiosis vaccination.

Six-week-old Leghorn chickens, which had been adapted to both their environment and cage mates, were orally inoculated with 400 Eimeria tenella oocysts as a means of low-dose vaccination. At 2, 3, 4, 5 or 6 days after vaccine administration, the birds were subject to 24 h of social stress through a prescribed method of random redistribution. Two weeks after vaccine administration, the birds were challenged by oral inoculation with 8000 oocysts. Caecal lesion scores were determined 6 days after challenge. Vaccinated chickens were more resistant to lesion formation than unvaccinated controls, and protection, as determined by lower lesion scores, was significantly enhanced when stress in the form of social disruption was applied on the fourth day following vaccine administration.