Morphology of medullary bone during the egg formation cycle.

The medullary bone of birds is known to function as a calcium store for egg shell production, but it is not known if the stage of shell formation within the egg formation cycle is reflected by the thickness of osteoid seams on the medullary bone. Adult laying hens were killed at two points in the formation cycle to determine the effects of shell formation on medullary bone using histological techniques. No differences in medullary bone volume or osteoid thickness were apparent at either of the two points. Fluorochrome bone labelling techniques demonstrated, however, that less medullary bone mineralisation occurred during the active period of shell formation.