Abstract
The present experiment was undertaken to investigate the effect of environmental temperature on plasma levels of catecholamines (epinephrine and norepinephrine). Chicks were preconditioned by feeding a basal diet (3, 250kcalME/kg and 200gcrude protein/kg) made mainly from ground yellow corn, dehydrated alfalfa meal, and purified soybean meal. The basal diet was fed ad libitum for preconditioning periods (from 12 to 15 days of age). During the experimental period (from 15 to 27 days of age), all the chicks were pair-fed by force-feeding 3 times a day (at 10:00, 15:00 and 19:00) to equalize intakes at the various temperatures. Temperatures studied were 16, 25 and 34°C and relative humidity was maintained at 50-70%. At the end of the experimental period, the birds were killed and blood samples were collected in heparinized test tubes at around 13:00h for determination of plasma levels of epinephrine and norepinephrine. Epinephrine and norepinephrine were measured by HPLC. Circulating plasma levels of epinephrine and norepinephrine in the cold condition (16°C) were significantly higher than the control (25°C). However, hot condition (34°C) had no significant effect on plasma level of epinephrine while it increased norepinephrine. This indicates that catecholamines may have different roles to tolerate the cold or the stressful heat environ-ment.
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