On the Control of Calcium Secretion in the Avian Shell Gland (Uterus)

Shell glands (SGs) of white Leghorn hens were perfused in situ to determine the time course and magnitude of secretion of egg shell Ca and factors that control secretion, during laying cycles. With a surrogate wax egg present in the SG during all test periods (substituted for the natural egg when necessary), net Ca secretion averaged 20 µm/h/g dry wt before a natural egg arrived in the SG (1-4 hr after ovulation), increased sharply as an egg arrived (h 5-6) progressing to 150 µm/h/g (h 14-18) and returned to basal levels (by h 24) when a shell was completed, but 2 h before the egg normally left the SG. Secretion rates in SGs were always greater when distended in egg-like fashion than when not, but rates in active (shell forming) SGs whether distended or not were always substantially higher than in inactive controls. Ca secretion in the mature magnum and in SGs of mature prelaying hens and pullets was minimal (