Stress and acid-base balance in chickens

Abstract

Two trials were conducted to study the effects of continuous infusion of adrenocorticotropic hormone (ACTH) on acid-base balance in broiler chickens. Osmotic pumps delivered 8 IU of ACTH in saline/kg of BW/d for 7 d or the same saline volume as used in ACTH at 1 µL/h for 7 d. Blood samples were taken on d 0 (baseline values) and on d 4, 7, and 14 after onset of the infusions. The ACTH treatment increased the hematocrit, partial pressure of CO₂, anion gap, corticosterone, mean corpuscular hemoglobin concentration, the blood concentrations of hemoglobin and HCO^3-, and reduced the partial pressure of O₂, plasma concentrations of Na⁺, K⁺, and Cl^-. Blood pH values and plasma concentrations of Ca²⁺ were unaffected by ACTH treatment. The ACTH infusion also resulted in a significant increase in plasma glucose, cholesterone, high-density lipoprotein, and triglyceride. There were no differences in any of the blood constituents measured from control groups. Results indicate that infusion of ACTH resulted in changes in plasma acid-base status along with changes in other blood metabolic variables. However, the ACTH treatment did not prevent homeostatic regulation of acid-base balance, as indicated by constant blood pH. There was, however, an increased need for O² to support gluconeogenic energy production; the birds responded by increased erythropoiesis. This adaptive response provided greater numbers of erythrocytes and thus a higher amount of circulating hemoglobin to deliver O² for metabolism.