Multiple concurrent stressors in chicks. 3. Effects on plasma corticosterone and the heterophil:lymphocyte ratio

Effects of multiple concurrent stressors on female Hubbard x Hubbard chicks were studied in a 2(6)-factorial experiment that employed as stressor treatments aerial ammonia (A, 0 or 125 ppm), beak trimming [B, sham handled or beak trimmed/cauterized on trial Day 1 (posthatch Day 10)], coccidiosis (X, gavage with 0 or 6 x 10(5) sporulated Eimeria acervulina oocysts), intermittent electric shock (E, 0 or between 2.9 and 8.7 mA), environmental heat stress (H, air temperature 30.4 or 34.8 C), and continuous noise (N, 80 or 95 dB). Plasma corticosterone concentration on trial Day 7 was unaffected by any stressor or stressor combination, but the heterophil:lymphocyte ratio (H/L) was increased by A, E, and H. Also, the B x X interaction was significant for H/L. The H/L increased linearly from .53 to .86 as number of concurrent stressors increased from zero to six. These findings indicate that the chick's leukocyte changes in response to stress are less variable and more enduring than its corticosterone response, and H/L are sometimes a more reliable indicator of stress.