Histologic Effects of Concurrent Heat Stress and Coccidial Infection on the Lymphoid Tissues of Broiler Chickens

SUMMARY We characterized the histologic effects of two stressors (heat and coccidial infection) alone or in combination on bursa of Fabricius, thymus, and spleen in broiler chickens. Four hundred and eighty Cobb500 male chicks at 14 days of age were randomly assigned to two treatments in a 2 × 2 factorial design, with 15 replicates per treatment and eight birds per replicate. The treatment factors were temperature (25 and 35 C) and a mixed culture of 2.5 × 105 sporulated Eimeria acervulina and Eimeria maxima oocysts (infection or no infection). Histologic lesion severity was scored in these tissues at different ages. At 21 and 28 days of age, bursal and thymic tissues from birds raised at 35 C exhibited significant increases in lymphoid depletion severity compared with those raised at 25 C. No significant differences were detected in the lymphoid depletion severity of birds infected with Eimeria when compared with uninfected birds. These results indicate that continuous exposure to heat stress–inducing te...