Jejunal calcium permeability in laying hens during egg formation.

The permeability of the upper jejunum to water, calcium, potassium, sodium and chloride was measured in the immature pullet and then in the laying hen before and during egg-shell calcification by an in vivo perfusion procedure. Jejunal calcium permeability was constant throughout egg formation. Thus, the increase of net absorption during shell calcification was not due to enhanced mucosal capacity for calcium translocation, but rather to a better solubilization of calcium carbonate in the upper digestive tract. However, this capacity increased at the onset of egg production, as shown by the difference between immature and mature birds.