Heat stress may impair immune system in broilers

Heat stress in broilers induced lesions of lymphoid tissues, indicating immune system impairment, but it’s not yet known if heat stress affects the vulnerability or severity of coccidiosis, Bryan Aguanta, a graduate student at the University of Georgia, told Poultry Health Today.

Aguanta and colleagues investigated the histological changes in broilers subjected to heat stress and coccidial infection. In their study, 14-day-old birds were randomly assigned to receive heat stress and some were not. Within each group, half of the birds were infected with Eimeria and some were not. The heat-stressed birds were exposed to a temperature of 95° F (35° C) from 15 to 28 days of age.

Sampling of birds from each group demonstrated that birds subjected to higher temperatures had more severe lymphoid depletion of the bursa and thymus at 28 days of age, indicating immune system impairment and therefore a handicap in the ability of handle disease, he said.

Aguanta and colleagues next plan to explore the immunological implications of heat stress as it relates to coccidiosis.

Interestingly, he noted, a student colleague has noted decreased coccidial-oocyst shedding in heat-stressed birds, indicating heat might actually induce protection against coccidiosis. It’s an interesting theory, though no one would want to intentionally expose broilers to high temperatures since heat has other negative production consequences, Aguanta added.