Oviducts and Salpingitis

Reading Time: 5 minutes

Chickens are the original egg assembly factories. Inside those fluffy bodies are conveyer belts where eggs are “built” through assembly-line techniques. 

A hen doesn’t need to mate to lay eggs, but the eggs will be infertile. The hen’s reproductive system consists of the ovary (where the yolk develops) and the oviduct (where the egg is built). The oviduct is a twisted tube-like organ about 26 inches long. It’s divided into five major sections: the infundibulum, magnum, isthmus, shell gland (uterus), and vagina. 

A baby hen’s ovary contains all the ova it will ever have. As the chick matures, hormones (and light) stimulate the ovary to begin converting ova to yolks. Interestingly, hens have two ovaries, but only one works. The right ovary stops developing and becomes dormant when the female chick hatches, but the left one continues to mature. In certain cases where the left ovary is damaged, the right ovary can replace it. 

Near the junction of the hen’s uterus (shell gland) and vagina are deep glands that can store sperm. In most birds, sperm remains viable at body temperature for 10 to 14 days. When a hen lays an egg, sperm is squeezed out of these sperm host glands into the oviduct, then migrates up the tube to fertilize a yolk. 

A mated hen won’t lay fertile eggs until seven to 10 days after mating, since it takes that long for the sperm to reach the oviduct. However, after that waiting period — even if she doesn’t mate again — she will lay fertile eggs for about two weeks from that one mating. To lay a continuous supply of fertile eggs, a hen will need exposure to a rooster on a regular basis. 

The Conveyer Belt 

So how does a hen’s oviduct work? 

About 15 minutes after an egg is laid, the hen ovulates and releases a yolk. This is captured by a funnel-like portion of the oviduct called the infundibulum where fertilization (if it occurred) takes place. If an egg has a double yolk, it means two yolks were released from the ovary at the same time. 

At this point, different sections of the oviduct supply various elements of the egg as it moves along the conveyer belt. 

Step one: The yolks pass through a portion of the oviduct called the magnum, where the albumen (white) is deposited around the yolk. This is the longest section of the oviduct at about 13 inches. As the albumen forms, the yolk rotates and twists the albuminous fibers to form the chalazae, which are ropey strands of egg white that anchors the yolk in place. This first step takes about three hours. 

Step two: In the portion of the oviduct called the isthmus, the inner and outer shell membranes are formed, and water and minerals are added. At this point, the egg has reached its full size and shape but has no hard shell. During formation, the egg moves through the oviduct small end first. This second step takes about 75 minutes. 

Step three: The egg now passes to the uterus portion of the oviduct where the egg acquires its shell and shell color. The shell consists mostly of calcium carbonate. This third step takes about 19 to 21 hours. 

Step four: The egg pauses for a few minutes in the muscular vagina where the bloom (or cuticle) is added and the egg is rotated so it’s laid large-end first. The hen then pushes the egg through the cloaca and vent in the final step call oviposition. 

Egg Anomalies 

Given the sophistication of this conveyer-belt process, it’s hardly surprising when occasional anomalies occur. 

Small eggs. These are the beginner eggs laid by young hens whose reproductive systems are just coming “online.” It takes a while for their bodies to get the hang of things. 

Shell-less eggs. Encased in nothing but the inner membranes, shell-less eggs are soft and floppy. While healthy hens will lay an occasional shell-less egg under even the best circumstances, shell-less eggs can be caused by youth (young pullets whose reproductive system is still maturing), old age (when the reproductive systems slow down), nighttime disturbance such as predators (which can interrupt the internal egg-forming process), too much salinity (such as watering your birds with soft water), or a defective shell gland (a fairly rare situation). 

Blood-stained eggs. As any mother can tell you, it takes a lot of oomph to push something large out of one’s body. Especially for young hens, the vent takes time to stretch enough to accommodate eggs, so some blood isn’t unusual. 

Wrinkled or rough eggs. A slightly wrinkled shell, called “body check” eggs, is sometimes the result of a hen’s body trying to repair some internal damage, such as a tiny crack. Other times it can result from stress, such as after a nighttime disturbance. Once in a while, an egg has rough patches or pimples on it. Roughness can sometimes be caused by too much calcium in a hen’s diet, which can happen during a dietary transition period (say, spending more time indoors due to winter). Extra calcium spots can also be laid down on a shell in the hen’s reproductive tract if she’s not getting enough water in her diet, so make sure the ladies have ice-free water during winter. 

Strangely pigmented eggs. Pigmentation is added to the shell in the uterus (or shell gland). The default color for all eggs is white. The different colored eggs found among different breeds depend on which pigments, and in what order, are applied to the shell. 

Misshapen eggs. Sometimes eggs are flattened on one side, or long and skinny, or pimpled, or bumpy, or spotted, or numerous other variations. Remember the conveyor belt. Sometimes a mistimed second egg bumps into the first egg still moving down the oviduct, causing a flat shell. Sometimes an egg stays too long in the shell gland, causing a flat side and wrinkles. Unless the hen appears unhealthy, misshapen eggs are perfectly fine to eat and just add character to your flock. 

Lash eggs 

Once in a great while, a hen will lay a horrible concoction called a “lash” egg (more accurately termed a “caseous exudate”). These are not true eggs, but instead are the result of a bacterial or viral infection that causes the hen’s oviduct to become inflamed, a condition called “salpingitis.” The hen’s immune system tries to wall off the infection with a cheese-like waxy pus mass which may or may not contain components of a regular egg (yolk, white, eggshell). It often contains tissue from the oviduct wall or blood. 

A lash egg is a very serious condition and is often fatal. Salpingitis is the most common cause of death in laying hens, and death usually happens within six months. Even if a hen recovers, she may never be able to lay eggs again. 

The conditions causing lash egg are not necessarily infectious between birds but can affect more than one bird in a flock due to similar conditions such as obesity or poor nutrition. Vaccinated chicks often prevent this condition later in life. Antibiotics can be useful, but since the symptoms often do not appear until after a hen is afflicted, their usefulness may be limited. It might be best to put the hen out of her misery and make sure the rest of the flock has clean conditions and proper nutrition. 

Back to Normal 

Fortunately, 99% of the time your ladies will lay fine eggs, or eggs with character. Gathering eggs and enjoying their fresh flavor is one of the nicest aspects of a homestead. 

Originally published in the Backyard Poultry Special Subscriber 2020 issue — Comb to Tail Health — and regularly vetted for accuracy.