Age and gender influence the cardiorespiratory function and metabolic rate of broiler chicks during normocapnia and hypercapnia

• We evaluated the gender and age influence on physiological responses to hypercapnia in chicks.
• We compared the cardiorespiratory and metabolic responses to CO2 in males and females chicks.
• The d21 female chicks seem to be more sensitive to hypercapnia.

Pulmonary ventilation (V⋅E), body temperature (Tb), mean arterial pressure (MAP), heart rate (fH) and metabolic rate (V⋅O2) were measured in 10 (d10)- and 21 (d21)-day-old male and female chicks exposed to 7% CO2. Under normocapnia, V⋅E was higher in d10 chicks than in d21 due to a higher tidal volume; in females a higher respiratory frequency (fR) was also observed. The d10 birds presented higher fH and V⋅O2. The d21 females showed the highest CO2 ventilatory response due to increased fR. MAP did not change during hypercapnia while a hypercapnic bradycardia occurred, except in d21 females. Hypercapnia induced a drop in Tb in all groups and an increase in V⋅O2 in d21 males. Overall, no gender effect is observed in cardiorespiratory and metabolic variables in d10 and d21 chicks under normocapnia, the differences in V⋅E and fH between ages may be related to distinct metabolic demands of these phases. The d21 female chicks seem to be more sensitive to hypercapnia.