Effect of ambient temperature and light intensity on physiological reactions of heavy broiler chickens

The effects of ambient temperature, light intensity, and their interaction on blood acid-base balance, metabolites, and electrolytes in broiler chickens under environmentally controlled conditions were examined in 2 trials. The experiment consisted of a factorial arrangement of treatments in a randomized complete block design. The 9 treatments consisted of 3 levels of temperatures (low = 15.6°C; moderate = 21.1°C; high = 26.7°C) from 21 to 56 d of age and 3 levels of light intensities (0.5, 3.0, 20 lx) from 8 to 56 d of age at 50% RH. A total of 540 Ross 708 chicks were randomly distributed into 9 environmentally controlled chambers (30 male and 30 female chicks/chamber) at 1 d of age. Feed and water were provided ad libitum. Venous blood samples were collected on d 21 (baseline), 28, 42, and 56. High ambient temperature significantly (P [less-than or equal to] 0.05) reduced BW, partial pressure of CO₂, bicarbonate, hematocrit, hemoglobin, K⁺, and Na⁺ along with significantly (P [less-than or equal to] 0.05) elevated pH level, Cl⁻, glucose, osmolality, and anion gap concentrations. Partial pressure of O₂ was slightly increased in response to increased ambient temperature. There was no effect of light intensity on most of the blood variables examined. Acid-base regulation during high ambient temperature and light intensity exposure did not deteriorate despite a lower partial pressure of CO₂, which consequently increased blood pH because of a compensatory decrease in HCO₃⁻ concentration. Plasma corticosterone was not affected by temperature, light intensity, or their interaction. These results indicate that continuous exposure of broiler chickens to varying light intensities had a minor effect on physiological blood variables, whereas high ambient temperature markedly affected various blood variables without inducing stress in broilers.