Abstract But egg production in chicken, as

Abstract

The female reproductive system of the poultry
is comprised of unpaired ovary and oviduct. The ovary is dark brown to black in
colour with several ovarian follicles
concentrated on the ventral surface. The ovary is attached to the bodies of the
lumbar vertebrae by a thin ligamentous structure known as mesovarium. The
ventral surface of the ovary is covered by the developing follicles. In adult
birds, the left oviduct appeared as a long convoluted and highly vascular tube.
The infundibulum, the first portion of the oviduct is composed of a cranial funnel-shaped part and a caudal narrow tubular
part. The funnel-shaped part opened
towards the left ovary by a wide slit like structure. The magnum, the second
portion of the oviduct is the largest in size and diameter, and most convoluted
part in laying birds. The isthmus, the third region of the oviduct is a narrow
tube while the shell gland region which is the fourth portion is an expanded pouch-like structure where the eggshell is deposited. The vagina is a short
muscular s-shaped tube connecting the
uterus to the cloaca. The highly distensible nature of the vagina allows for the passage of hard-shelled egg during oviposition

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Keywords:
Poultry, female, reproductive system, anatomy, physiology

 

2.1
Introduction

It is important to
understand the anatomy and physiology of the reproductive system of female
chicken so that its reproductive activities can be well appreciated. In
domestic chickens, reproduction is sexual, and it takes both the male and
female gametes to unite in order for a new life form to be produced. But egg
production in chicken, as in various avian species, is not dependent on the availability of male sexual gamete. This means
that a female chicken can lay eggs without being mated by a male 1.

A matured female
chicken is referred to as “Hen”, while the growing young is commercially
referred to as “Pullet”. Like other birds, a chicken
lays an egg
which later hatches (if fertilized) to
bring forth offspring, unlike mammals
which give birth to young ones alive. One striking difference between mammals
and avian species with respect to reproductive physiology is the fact that
mammalian embryos develop inside the body of the female in special organs adaptive
to the function of maintaining the embryo till “term”, and have the potentials
to deliver the young ones alive 1, 2. In this situation, the offspring
obtains its nutrients requirement from the dam’s circulatory system till it
matures and is delivered. The avian differs from this, in that the embryo
develops outside the parent and its nutritional requirements during and shortly
after incubation is fixed in the eggs
prior to lay.

The
anatomy of the female reproductive system of a chicken is divided into two
distinct parts viz: the ovary (site of sex steroid synthesis, gametogenesis, and yolk formation) and the
oviduct (organ receiving the egg yolk during ovulation and successful
depositing the egg white, shell membrane and the shell) 1. In the majority of
the avian species including domestic chicken, only the left ovary and oviduct
are functional. The right ovary and its associated oviduct are initially
present in the embryo but regress during development to adult birds. This
characteristic of the single left avian
reproductive tract (ovary and oviduct) dates back to enantiornithine birds from
the early cretaceous
period 2.

 

2.2 The Ovary

The normal reproductive tract of matured hen consists of a left ovary appearing as a bunch of grape as reported by Gilbert 3 in chicken
(Figure 2.1), Vijayakumar et al. 4 in
emu (Dromaius novaehollandiae) and Rao 5 in domestic duck (Carina moschata).
The right ovary and oviduct are present in the embryonic stages, but these
tissues normally regress in most avian species. The ovary is dark brown to
black in colour with several ovarian
follicles concentrated on the ventral surface 6 and in the young bird; the
ovary is flat with inverted L shape. The left ovary is located in the anterior
body cavity left to kidney and adjacent to the adrenal gland and weighs about
300 mg in newly hatched chicks. The lengths of the ovary in laying and non laying birds were 28.63 cm and 18.02 cm,
respectively as reported by Vijayakumar
et al. 4 in the emu. The mean
weight of the left ovary in laying emu was 349.66 gm which decreased to 103.66
gm in the non-laying emu. The ovary is
attached to the abdominal wall by the mesovarium ligament in birds. A large body of follicles is found in the ovary
which later matured serially and the ovary receives its blood supply from the
ovarian artery, which arises from the left reno
lumbar artery or from the dorsal aorta 4, 7. The ovary consists of a highly vascularized
inner area (medulla) and an outer area
(cortex) which presents granular aspects as earlier as 5 weeks of age due to
the progressive development of follicles.
It grows rapidly between 16 and 20 weeks of age and its
weight increases from 5 to 60 g during this period and can reach up to 120 to
150 g in breeder hens fed ad libitum
8. The development of ovary in chicken starts at hatching, and it grows to
attain full development at the time of sexual maturity. Some thousands of eggs
are formed in the ovary at the time of hatching, but most eggs do not develop
to ovulatory size, thus, fewer eggs are laid by a hen in its live time
comparatively.

According
to Kaspers 10, a pre-ovulatory egg, otherwise called ovum, develops from a
single cell covered by a vitelline membrane to which egg yolk is added. About 2
to 3 weeks before the onset of lay, small (