Mia Patel
Unlike most female animals, which have two functioning ovaries, the chicken usually has only one. The female chicken reproductive system is made up of the ovary and the oviduct. The ovary is a cluster of sacs attached to the hen's back about midway between the neck and the tail. In almost all species of birds, including poultry, only the left ovary and oviduct are functional. The right ovary stops developing when the female chick hatches, but the left one continues to mature.
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What You'll Learn
The left ovary is the functional one
In almost all species of birds, including poultry, only the left ovary and oviduct are functional. The female chicken embryo has two ovaries, but only the left one develops and matures to produce eggs. The right ovary typically regresses during development and is non-functional in adult birds.
The ovary is a cluster of sacs attached to the hen's back, roughly midway between the neck and the tail. It is fully formed when the chicken hatches and contains several thousand tiny ova, each within its own follicle. As the hen matures, these ova develop into yolks, a few at a time. The ovary can be observed to have two well-differentiated regions: the cortex and the medulla.
The yolk is completely formed in the ovary. When a yolk is fully developed, its follicle ruptures, releasing it from the ovary and into the infundibulum, the entrance of the oviduct. The infundibulum is the first part of the oviduct, a tube-like organ lying along the backbone between the ovary and the tail. It is funnel-shaped and collects the yolk after its release from the follicle. The yolk remains in the infundibulum for around 15 minutes, during which time fertilisation takes place if the hen has mated.
The oviduct is divided into five major sections, each with a different function: the infundibulum, magnum, isthmus, shell gland, and vagina. All of the other parts of the egg are added to the yolk as it passes through the oviduct. The chalazae, albumen, shell membranes, and shell are formed around the yolk to make a complete egg, which is then laid. This entire cycle usually takes a little over 24 hours.
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The right ovary stops developing
In almost all species of birds, including poultry, only the left ovary and oviduct are functional. The right ovary stops developing during a female chick's early development. Although the female embryo has two ovaries, only the left one matures. The right ovary typically regresses during development and is non-functional in the adult bird.
The right ovary's regression is a natural part of a chicken's growth. It is a process that begins early in a female chick's life and is necessary for the proper functioning of the bird's reproductive system. This process is known as atresia, which is the normal physiological process of tissue regression.
The left ovary is the only functional ovary in chickens, and it is responsible for producing eggs. The ovary is a cluster of sacs attached to the hen's back about midway between the neck and the tail. It is fully formed when the chicken hatches and contains several thousand tiny ova, each within its own follicle. As the hen matures, these ova develop into yolks.
The yolk is completely formed in the ovary. When the yolk is fully developed, its follicle ruptures, releasing it from the ovary and into the infundibulum, the entrance of the oviduct. The oviduct is a tube-like organ that lies along the backbone between the ovary and the tail. It is divided into five major sections, each with a specific function in egg production.
While the right ovary does not develop in chickens, there have been rare cases where the left ovary has been damaged, and the right ovary has developed to replace it. This showcases the potential for the right ovary to become functional if necessary.
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The ovary and oviduct
The female chicken reproductive system is made up of two parts: the ovary and the oviduct. In almost all species of birds, including poultry, only the left ovary and oviduct are functional. Although the female embryo has two ovaries, only the left one develops. The right one typically regresses during development and is non-functional in the adult bird.
The ovary is a cluster of sacs attached to the hen's back about midway between the neck and the tail. It is fully formed when the chicken hatches and contains several thousand tiny ova, each ovum within its own follicle. As the female reaches maturity, these ova develop a few at a time into yolks. As the ovum develops and gets larger, a clear line called the stigma line appears. This is where the yolk is released. On the surface of every egg yolk, there is a tiny, whitish spot called the blastodisc. This contains a single female cell.
The oviduct is a tube-like organ lying along the backbone between the ovary and the tail. In a mature hen, it is approximately 25 to 27 inches long. The yolk is completely formed in the ovary. When a yolk is fully developed, its follicle ruptures, releasing it from the ovary. It then enters the infundibulum, the entrance of the oviduct. The infundibulum is the first part of the oviduct and is 3 to 4 inches long. It engulfs the ovum released from the ovary. The yolk remains in the infundibulum for 15 to 17 minutes. Fertilization, if it occurs, takes place here. The remaining parts of the egg are added to the yolk as it passes through the oviduct. The chalazae, albumen, shell membranes, and shell are formed around the yolk to make the complete egg, which is then laid. This cycle usually requires a little more than 24 hours.
The oviduct consists of five distinct parts or sections, each with different functions. These sections are the infundibulum (or funnel), magnum, isthmus, shell gland, and vagina. The infundibulum collects the yolk after its release from the follicle and directs it into the oviduct. This section has very thin walls and is 6-9 centimetres long. Fertilisation of the ovum by the male sperm occurs here. The magnum is approximately 40 centimetres long and secretes more than 40% of the albumen. The isthmus is about 12 centimetres long and secretes some albumen and the shell membranes. The shell gland is also about 12 centimetres long and secretes about 40% of the albumen and the egg’s shell. Lastly, the vagina is about 12 centimetres long and secretes the egg’s outer cuticle and possibly the shell pigment.
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Oviduct's five distinct parts
In chickens, the female reproductive system is made up of two parts: the ovary and the oviduct. In almost all bird species, including poultry, only the left ovary and oviduct are functional. The right ovary typically regresses during development and is non-functional in adult birds.
The oviduct is a tube-like organ that lies along the backbone between the ovary and the tail. It is a twisted tube that is about 25 to 27 inches long when fully developed and is divided into five major sections: the infundibulum, magnum, isthmus, shell gland, and vagina.
The infundibulum is the first part of the oviduct and is about 3 to 4 inches long. It is a funnel-shaped opening near the ovary that catches the egg and facilitates the entry of the ovum into the oviduct. The yolk stays in the infundibulum for about 15 to 17 minutes, and fertilization, if it occurs, takes place here. The infundibulum is attached to the body wall and is closely associated with the left abdominal air sac.
The magnum is the second part of the oviduct. It is in this tubular section that a thin and dense layer of albumin is added to surround the yolk. Some species have a sperm host gland in this area to store sperm for later fertilization.
The isthmus is the third part of the oviduct. It is a narrow, rounded, and firm muscular part of the tube that connects the magnum to the shell gland. The isthmus contains a large number of secretory cells and is responsible for transporting the fertilized ovum (embryo) to the shell gland.
The shell gland is the fourth part of the oviduct. It is in this part of the oviduct that the chalazae, albumen, shell membranes, and shell are formed around the yolk to make a complete egg.
The vagina is the fifth and final part of the oviduct. It is through the vagina that the fully formed egg is laid.
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The process of ovulation
In chickens, only the left ovary is functional. The right ovary stops developing during the embryonic phase or when the female chick hatches. The left ovary is a cluster of sacs attached to the hen's back about midway between the neck and the tail. It is fully formed when the chicken hatches and contains several thousand tiny ova, each ovum within its own follicle.
Ovulation is the process in which the yolk (ripe ovum or oocyte) is released from its follicle in the ovary and is received into the oviduct through its infundibulum. The oviduct is a twisted tube that is 25 to 27 inches long when fully developed and is divided into five major sections. These sections are the infundibulum, magnum, isthmus, shell gland, and vagina. The first part of the oviduct, the infundibulum (or funnel) is 3 to 4 inches long and engulfs the ovum released from the ovary. The released yolk stays in place, and the muscular infundibulum moves to surround it. The yolk remains in the infundibulum for 15 to 17 minutes. Fertilization, if it is going to occur, takes place in the infundibulum.
After the infundibulum, the ovum moves further along the oviduct via the magnum. The magnum is the longest part of the oviduct. Most of the albumen formation takes place in the magnum, and this process lasts about 3 to 4 hours. The chalazae and albumen form around the yolk mass as it is propelled in a rotating motion by rhythmic peristalsis, resulting in the characteristic structure of the chalazae. The chalazae are made up of protein fibres that connect the yolk with the shell membrane, ensuring the central position of the yolk. The albumen is not homogeneous, with different areas having different viscosities. After the magnus, the egg mass arrives in the Isthmus, where both the inner and outer shell membranes are formed.
The total time a hen’s body takes to transform a yolk into a fully developed egg and lay that egg is about 25 to 26 hours. Typically, about 30 to 75 minutes after a hen lays an egg, the ovary releases the next ovum. However, the female chicken reproductive system is sensitive to light exposure, especially the number of hours of light in a day. In chicken hens, ovulation usually occurs under normal daylight conditions and almost never after 3:00 p.m.
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Frequently asked questions
The left ovary and oviduct are functional, while the right ovary and oviduct are dormant.
While the female chicken embryo has two ovaries, only the left one develops further. The right ovary typically regresses during development and becomes non-functional in the adult bird.
The ovary is where ova (yolks) develop. When an ovum matures, it is released from the ovary into the oviduct, which is known as ovulation.
The oviduct is a tube-like organ that lies along the backbone between the ovary and the tail. It is divided into five major sections, each with a specific function, that completes the egg formation process.
The ovulation period of a hen is about 24 to 26 hours, and she will typically lay an egg each day for about six or seven days. This group of eggs is known as a clutch.
