Features of eggshell formation in guinea fowl: kinetics of shell deposition, uterine protein secretion and uterine histology

1. Rate of calcium carbonate deposition, duration of eggshell formation, or ganic composition of the uterine fluid, morphology of the egg shells and hi stochemistry of the uterus were studied in guinea fowl to analyse the origi n of such thick, strong egg shells. 2. The egg shell was linearly deposited from 6.4 h to 21.8 h after the ovip osition of the precious egg. The rate of egg shell deposition was similar t o that in laying hens. However, the duration of linear shell deposition was increased by 2.1 h relative to that in hens. This explained the increased egg shell weight observed in the guinea fowl. 3. Intervals between oviposition of intra-clutch eggs were 24 h throughout the laying period. Ovulation occurred just after oviposition of the previou s egg in the guinea fowl, as previously observed in hens but the duration o f egg white protein deposition, of plumping and of initiation of shell mine ralisation were all 1.5 h shorter than in domestic hen. 4. Uterine fluid can only be collected during the growth and terminal phase of shell formation. The electrophoretic profiles of the uterine fluid diff ered between phases and were somewhat different front those previously obse rved in the hen. Ovalbumin and ovocleidin-17 were both present in the uteri ne fluid and also in egg shell extract. Ovocleidin-17 was predominant durin g the growth phase. 5. The histology of the uterus differed slightly in guinea fowl compared to hens. Ovocleidin and ovalbumin are both secreted by the tubular glands. 6. Examination of radial ultrathin sections of eggshell showed, above the m ammillary layer, intricate interlacing of adjacent exospherite in guinea fo wl in contrast to the continuous columnar microstructure in hens. 7. The kinetics of egg shell deposition largely explains the increased egg shell weight of guinea fowl. The organic matrix proteins may be associated with the contrast between the structural organisation of the guinea fowl eg g shell and that of the hen egg shell.