Stage 1 (Fertilization)
The yolk is dropped from the ovary and fertilized by the male sperm. The fertilized yolk then travels down the egg canal and receives several coatings of albumen (egg white). The shell is then developed in the hen’s shell gland. This process takes approximately 20 hours; after which, the egg is laid.
Stage 2 (Days 1 and 2)
The egg is hatched and gradually cools. At this stage, embryonic growth slows and often stops. Many birds will develop a “clutch” of eggs that they wish to incubate.
The clutch size depends on a variance of factors including hereditary traits and environmental factors.
For artificial incubation, the breeder can actively choose the clutch size they wish to incubate. He or she may choose to store the eggs at room temperature (15-18°C) for up to 10 days in order to gather the required amount of eggs.
On the first day of incubation, embryonic growth begins again and the cells begin to divide and multiply rapidly. By the end of day one, the head, eyes, nervous system and circulatory system have begun to form. The heart is formed on day two and is functioning within 48 hours of incubation.
Stage 3 (Days 3 and 4)
On day three, the heart develops from its simple form to become a fully functioning, beating heart. Additional membranes are formed in this time. This creates the amniotic sack which the embryo will float in for the duration of incubation.
Within the amniotic sack; amniotic fluid, combined with correct egg turning, ensure the embryo orients itself correctly during hatching.
Although the heart is still positioned outside the body, by the end of day four, the legs and wing buds have begun to form.
Stage 4 (Days 5 – 10)
By the end of day six, the legs and wings are nearly complete. Feathers begin to appear at day eight, and by the end of day nine the embryo is beginning to look like a chick – the chicks heart is now in place within the body. By day ten, the bones are beginning to form.
Stage 5 (Days 11 – 21)
By day thirteen, the chick’s down feathers are fully formed and present on most of the chick’s body. The legs and wings are also complete with bones and muscle tissue. By day sixteen, the beak, leg scales and claws are very nearly complete. The remaining yolk then becomes a food source for the developing chick; this is used up by day nineteen.
At day nineteen, the chick is beginning to struggle to get enough oxygen to its blood; carbon dioxide levels in the chick’s blood begin to rise dramatically. A rise in the carbon dioxide level within the chick’s blood causes the chick’s neck to twitch; its beak is forced through the membrane sack into the air sack at the blunt end of the egg.
The beak then opens for the first time and the lungs inflate; fresh oxygenated blood is then circulated around the body. At this point in the incubation period, the chick is under significant stress; many chicks die at this stage of incubation because they are too weak or undernourished to deal with the stress they are under.
Stage 6 – Pipping (Day 20)
A day or so before hatching, the chick begins to “chirp”. Chirping is the sound made by the chick in an effort to communicate with its mother. The mother then naturally chirps back encouragement. In artificial incubation, some breeders enjoy chirping back to the chick to encourage it to hatch.
The chick continues to breathe from the air sack but soon begins to run out of air. This again begins to cause the chick’s neck to twitch involuntarily. At this stage the chick’s beak begins to penetrate the outer shell; this is known as “pipping”. The chick’s legs begin to move and twitch which causes the chick to move around inside the egg and the hole gets bigger. After an initial hole has been made, it is likely that the chick will pause (sometimes for up to 24 hours) to regain some strength and energy.
By the time pipping begins, egg turning should have ceased. This is very important as on day twenty, the chick gets itself into its ideal hatching position inside the egg; egg turning at this point would completely disorientate the chick and may result in injury or death.
Stage 7 – Hatching (Day 21)
On day 21, the chick will make a determined effort to chip off the top at the pointy end of the egg. The chick takes its first gasp of air as the top of the egg is released. It will usually rest for a while here, but will then go on to shake off the bottom half of the shell.
The hatching process takes time and the chick is visibly exhausted after its ordeal.
When the chick hatches it is likely to be wet, but all the yolk should be absorbed into the chick’s stomach. If there are any large pieces of yolk attached to the chick’s bottom that were not absorbed into its stomach, the chick has a hernia and unfortunately will not survive.
The newly hatched chicks will stagger clumsily around the incubator or nest stopping for frequent rests. Do not worry; it is often the case that some chicks appear very tired and unwell after they have first hatch. But after a short rest, chicks are very likely to spring back to life at the first sign of a stimulus.
Never turn off the incubator too early. Some eggs will naturally hatch later than others.
Leave the un-hatched eggs in the incubator for at least another 24 hours after the expected hatch day; you never know, they may just surprise you. Remember to resist the temptation to keep opening the incubator. Chicks are very sensitive to the cold and, by opening the incubator lid, valuable heat energy is lost. Chicks will happily remain in the incubator for 48 hours after hatching. They will not need any additional food and water during this time, as they will have enough food remaining in their bodies from their time inside the egg.