Progesterone and testosterone elicit increases in the duration of shell formation in domestic hens.

Injection of progesterone or testosterone in hens 4 and 10 h after ovulation increased the intervals between ovipositions and shell weights. The effects were dose-dependent. Expulsion of the egg from treated hens at the expected time of oviposition suppressed the increase in shell weight and deposition of the cuticle. The duration of shell formation had therefore been increased by the injections of progesterone or testosterone. Injections of progesterone 16 h or of testosterone 15 h after ovulation advanced oviposition and reduced shell weight. Testosterone propionate was more efficient than testosterone in its action on the duration of shell formation. Oestradiol was ineffective. Indomethacin delayed oviposition but did not change the duration of shell formation. These results suggest that the duration of shell formation is under the control of hormonal factors and that the larger follicles of the ovary, may be involved in its control.