No. J3 (August) Japanese issue

Review

(Vol.41:p.J142-J150)

Physiology of Egg-laying in the Guineafowl (Numida meleagris)

Hiroshi Ogawa

Department of Animal Science, Tokyo University of Agriculture, 1737 Funako, Atsugi-shi, Kanagawa 243-0034, Japan

Following are characteristics of the egg and the physiological mechanisms of egg-laying in the guineafowl :
1. The guineafowl egg is smaller and more spherical than the chicken (White Leghorn) egg, and the eggshell is heavier, thicker, and stronger. The guineafowl egg has a higher concentration of magnesium and smaller amount of albumen than the chicken egg.
2. The rapid growth phase is almost identical to that in the chicken, whereas there are cases where more than two follicles begin to enter the rapid growth phase in a day.
3. The ratio of the length of the magnum to the whole length of the oviduct is smaller in the guineafowl than in the chicken. Guineafowl showed a smaller weight increase of the oviduct in response to estrogen injection at 4 to 5weeks of age than in the chicken.
4. Estrogen receptors are present in the oviduct magnum and the maximum binding capacity (Bmax) is greater in the albumen secretion period for both the guineafowl and the chicken.  Bmax is lower in the guineafowl than in the chicken.
5. The mean interval between oviposition is estimated to be 24hours 22minutes with ovulation occurring less than 15minutes after oviposition. The difference in oviducal term of the ovum after ovulation is not large between the guineafowl and the chicken.
6. Plasma concentrations of calcium, phosphorus and magnesium at various times between ovipositions show a gradual decrease before oviposition. The ratio of inorganic calcium, phosphorus and magnesium to total calcium, phosphorus and magnesium is higher in the guineafowl than in the chicken, respectively.
7. Receptors for paratholmon or calcitonin present in the membrane fraction of the shell gland endometrium, the equilibrium dissociation constant, and the maximum binding capacity all change during eggshell formation.
8. Enlargement during the early period of eggshell formation is smaller, and larger amounts of minerals are deposited on the shell membrane in the guineafowl than in the chicken.
9. Histological conditions of the mucosal folds in the magnum and the uterus are different between the guineafowl and the chicken.
10. The effect of photoperiod on the onset of egg-laying is greater in the guineafowl than in the chicken. Oviposition occurs over a longer period of the day in the guineafowl than in the chicken.

(Japanese Journal of Poultry Science, 41 : J142-J150, 2004)

Key words : guineafowl, chicken, physiology, egg-laying, egg formation