CO2 and avian eggshell formation at high altitude

Area of Science:

• Animal Physiology
• Avian Biology
• Environmental Physiology

Background:

• Altitude exposure can induce hypocapnia (low CO2 levels) in birds.
• Hypocapnia is hypothesized to affect eggshell formation and gas exchange properties.

Purpose of the Study:

• To test if altitude-induced hypocapnia reduces eggshell conductance to water vapor (GH2O) in hens.
• To investigate the impact of hypocapnia on eggshell thickness and pore area.

Main Methods:

• Seven laying hens were exposed to different altitudes (1200 m, 3800 m) and conditions (3800 m with added CO2).
• Egg GH2O was measured gravimetrically.
• Shell thickness was measured, and aggregate pore area was calculated using Fick's law.

Main Results:

• At 3800 m, GH2O, shell thickness, and pore area were reduced compared to 1200 m.
• Relieving hypocapnia at 3800 m + CO2 further reduced GH2O and pore area, while increasing shell thickness.
• The initial hypothesis was rejected based on these findings.

Conclusions:

• Hypocapnia is responsible for thin eggshells at high altitudes.
• Other physiological factors, not hypocapnia, likely cause reduced eggshell GH2O and pore area at altitude.