Chickens lay a series of eggs, one a day, each one getting slightly later than the last, until it gets to late in the day, when they stop for a break. If a sufficient number of eggs are left in the nest, the hen may go broody and start to sit on them! If a cockerel has fertilised the eggs, the embryo doesn’t start to form until the eggs are warmed by the broody – fertilised eggs stay viable for a week or so – hence the hen laying a clutch and the brooding on them to incubate them.

The yolk is formed first in the ovary days before the egg is laid – when it is released occasionally a spot of blood is stuck to it. As it travels down the oviduct the egg white is added on. Further down the shell membrane is deposited and finally the shell is formed mostly from calcium carbonate over a period of about 20 hours. Brown eggs have their pigment added towards the end – it can be rubbed of with sandpaper or cleaned off with vinegar! Other colours may be added depending on the bred. Finaly the protective bloom coating is added to “seal” the porous egg from bacteria.

Chickens have one exit hole for urine and poops, called the “vent”. They do not have a bladder because their urine is not a fluid. It’s the white bit of their poo and is called “urates”. The cloaca is where the intestine, ureterus and oviduct come together into a common chamber. This is obviously pretty dirty, although eggs come out clean when laid.


The hen turns part of the cloaca and the last segment of the oviduct inside out, “like a glove.” The egg emerges far outside, at the end of the bulge and so doesn’t go anywhere near the “pooey” bit (cloacca). The emerging egg keeps the bowels shut, so the egg can’t get contaminated. That is why eggs are always clean when they are laid. They get dirty because the hen stomps around and makes a mess, before you get there!

Egg Bound

A hen is “egg bound” when she fails to lay her egg. This is a common condition, and may result from inflammation
of the oviduct, a malformed or double yolker egg, or a too large egg in a young pullet.
Some of the symptoms are…

• The bird seems very restless
• She will drink little and eat little
• She will tend to stand all hunched up
• She visits the nest regularly in an attempt to lay her egg
• Her oviduct may end up protrude due to excessive pushing by her to eject the egg; internal haemorrhage or exhaustion may occur and the fowl may die
• She may smell badly
• Her vent will look quite red and protrude
• She may have faecal matter that has built up behind the egg, if you see white liquid that will be her urates trying to pass.