We tested the hypothesis that altitude-induced hypocapnia in hens reduces eggshell conductance to water vapor (GH2O). Seven laying hens (Gallus domesticus) native to 1200 m were chronically exposed to high altitude (3800 m), and then to high altitude with sufficient inspired CO2 to relieve hypocapnia (3800 m + CO2). Egg GH2O was measured gravimetrically, shell thickness was measured with a micrometer, and aggregate pore area was calculated from measured values using Fick's law. Comparing results at 1200 m (n = 118) and 3800 m (n = 102), GH2O was reduced from 13.9 ± 0.2 to 12.6 ± 0.2 mg/(d·Torr) (mean ± SE), shell thickness was reduced from 0.297 ± 0.003 mm to 0.287 ± 0.03 mm, and calculated aggregate pore area per egg was reduced from 1.97 ± 0.03 mm2to 1.72 ± 0.03 mm2. When hypocapnia was relieved at 3800 m + CO2 (n = 82), GH2O was reduced even further to 11.1 ± 0.2 mg/(d·Torr), shell thickness increased to 0.305 ± 0.003 mm, and aggregate pore area was reduced 1.61 ± 0.03 mm2. Based on these results we reject our hypothesis. We conclude that hypocapnia is responsible for thin eggshells at altitude. Other physiological stimuli must cause the reductions in eggshell GH2O and pore area.
- Altitude, egg shell conductance
- Birds, hen
- Egg, shell conductance
- Hypocapnia, egg shell conductance
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine