Page 550 - Anatomy and Physiology of Farm Animals, 8th Edition

Poultry / 535

For fertilization to occur, spermatozoa
shell. The oviduct terminates in a slit‐like must reach the egg before it enters the
aperture in the urodeum, next to the open-
VetBooks.ir ing of the ureter (Fig. 30‐11). tubular segment of the infundibulum
where the first albumen layer will be
secreted to surround the egg. Spermatozoa
Egg Formation and Oviposition may be temporarily stored in the infundib-
ulum so that they can be readily available
The number of eggs laid consecutively by for the relatively short period that fertili-
wild birds during any period of egg laying is zation is possible. In the domestic hen,
termed a clutch. The number of eggs per the egg is in the infundibulum for about
clutch for a wild bird is considered to be 15 minutes. Spermatozoa are also stored in
related to the ability of the species to incu- specialized tubules in the uterovaginal
bate the eggs and raise the hatchlings and is region for longer periods. In the domestic
therefore dependent on the strain of the hen, spermatozoa remain viable for 7 to 14
species, age of the female, and phase of the days when stored here. Spermatozoa are
laying cycle. The time period between released from this site in association with
clutches for wild birds may extend to oviposition of each egg and migrate to the
months or years. Under typical manage- infundibulum to be available to fertilize the
ment practices for flocks of domestic chick- next egg. Ovulation of the next egg occurs
ens used for egg production, eggs do not about 30 to 45 minutes after oviposition of
remain with hens after the eggs are laid. the previous egg.
However, hens typically lay a number of Albumen (egg white) secretion around
eggs consecutively for several days and then the yolk begins in the infundibulum, but
interrupt laying for at least 1 day. Some refer the majority is secreted by the magnum.
to this pattern as a sequence of eggs, rather Albumen primarily consists of water, pro-
than a clutch. During a 12‐month laying tein, and minerals and is a source of these
period, hens may produce more than 300 nutrients for the developing embryo. Some
eggs by laying multiple sequences (clutches). of the proteins also have antimicrobial
The time period between ovulation and properties and protect against microor-
oviposition (expulsion of the egg) for the ganisms. The chalazae are two twisted,
domestic hen is about 24 to 26 hours. fiberlike structures that extend from
Ovulation of the next egg occurs after opposite sides of the yolk to each end of
oviposition of the preceding egg, so only the egg (Fig. 30‐12). These are formed from
one egg is in the oviduct at a time. As in fibers in the inner layers of the albumen
mammals, ovulation is preceded by a sud- when the yolk rotates as it passes through
den, rapid rise in LH, and this hormone the oviduct.
surge is believed to be responsible for The eggshell consists of four layers that
changes in the mature follicle about to be were applied to the outer surface of the
released from the ovary. Four to six hours albumen. From inner to outer, the layers
prior to the ovulation, plasma progester- are: (1) shell membranes; (2) mammillary
one and LH levels peak at the highest levels cores; (3) matrix; and (4) cuticle. The
seen in a laying cycle. The source of the combination of the mammillary cores and
progesterone appears to be the largest and matrix has also been termed the testa. The
most mature ovarian follicle. Unlike mam- innermost shell membranes permit the
mals, there is no corpus luteum formed on exchange of gases and water, but these
an ovary at the site of an ovulated follicle. membranes are not permeable to albumen.
Progesterone receptors are found in vari- As eggs age, the inner and outer shell
ous sites throughout the oviduct, where membranes tend to separate at the large
progesterone may promote secretions and end of the egg, and an air cell is formed
muscular contractions for egg develop- (Fig. 30‐12). The size of an air cell
ment and transport, respectively. increases as an egg continues to age.