Incubation and hatching

Before you incubate eggs:

Preparation and patience are the keys to success with incubation. 

Get to know your incubator. I know that most first time hatches cannot wait to get their eggs in the incubator but to avoid problems it is imperative to run it for at least 24 hours at the correct temperature before you even consider adding eggs. 

Check your turning device before the start of each incubation cycle. Turning failures, depending on when they happen, are detrimental to results. It is as important to check and maintain manual egg turning devices to prevent a breakdown or damage to the eggs during incubation.

Site your incubator away from radiators, heaters, the sun and draughts. The best location will have a stable temperature and humidity like a spare room or garage.

Select the best eggs. Most producers set as many eggs as their breeders produce and this is not the best way to manage your flock. If incubator space is the limiting factor, it is more profitable to select the better quality eggs for incubating.

Select breeders with care. Bright eyes, red full combs and peak condition. I once had an old keeper tell me never to breed from a bird that had been ill or out of condition in the last 12 months. As he had been keeping chickens for more years than I have been alive it is advice I have followed.

Below: A trio of Wyandotte breeders.

Have the brooding area ready with spare light bulbs if that’s what you intent to use as a heat source. And make sure it all works. There is nothing worse than plugging an electric hen in and finding it does not work when you chicks are ready for the brooder.

Below: Have your incubator set up and running before you need it.

Preparation for incubation is very important. Eggs need to be carefully selected to make sure they are clean, free from cracks and blemishes and to make sure they are the best to preserve the breed standard.

For Barnevelders this means selecting the deep brown speckled eggs of good size. Avoid misshapen eggs or any with ridges. Large eggs are less likely to be fertile and seem to hatch badly and small eggs will produce small chicks which by definition will take longer to grow up.

When choosing hatching eggs there are a few things you should do: 

•    Select eggs from breeders that are mature and healthy. 

•    Compatible with their mates and producing a high percentage of fertile eggs.

•    Well fed with added greens and supplements if necessary.

•    Avoid large, small or misshapen eggs. Large eggs hatch poorly and small eggs produce small chicks.

•    Avoid eggs with cracked or thin shells. These eggs have difficulty retaining moisture needed for proper chick development. Penetration of disease organisms increases in cracked eggs.

Candling Eggs before Incubation:

You should candle your eggs before you set them. There are a few problems that can be avoided with a few minutes and a bright light.

Below: It is pointless to incubate an egg like this one below, it has no yolk.

An egg like this one is too porous. the shell is thin, uneven and has a flaky feel to it. The chick gets all of the calcium it need for it's skeleton from the shell so it will be deficient from the start. A weak shell will allow pathogens easy entry.

Below: Porous shells should be avoided.

If membranes have not formed correctly or eggs have been damaged in transit you get a detached air cell. You can see it moving around.

Below: Damaged membranes won't produce viable chicks even if fertile.

Candling before you incubate can show cracks and damage to the shell that is not visible to the naked eye.this egg below has a crack, is dirty and has water damage to the side.

Below: Damaged and dirty eggs are no good.

What should an egg look like under the candling lamp? Below is good example even though it was taken as clear from one of my clutches at 10 days. There is a yolk shadow and air cell where it should be and no obvious defect to the shell.

Below: A normal but infertile egg with the yolk shadow and air cell visible.

Ventilation during incubation:

Ventilation is very important during the incubation process. It often gets overlooked. While the embryo is developing, oxygen enters the egg through the shell and carbon dioxide escapes in the same manner.

As embryos grow open the air vents to meet increased embryonic oxygen demand. Take care to maintain humidity during the hatching period. Unobstructed ventilation holes, both above and below the eggs, are essential for proper air exchange.

As the chicks hatch, they need an increased supply of fresh oxygen. This is the main reason for the pip that appears around day 19 to 20. The chick will broach into the airspace and then push a hole in the shell to breathe.

What to use to clean the incubator.

Wash the bits you can with hot soapy water. Use your noggin and do not get the electrics or turning motor wet.

Vacuum the fluff or down out of the hard to reach places.

I use a baby-bottle sterilising liquid and a mild bleach solution. Use 10ml of bleach to one litre of warm water.

To wash eggs or not, that is the question?

Some people say not to clean eggs before incubation, others swear by it. I have had my fair share of failures and one exploding egg in an incubator will ruin your day. The smell and the mess have to be seen to be believed.

In the past I have had it put to me that mother nature does not clean her eggs before incubation and there is a protective layer around the eggs, called the cuticle or bloom that protects them by preventing bacteria from entering the egg through the pores of the shell.

Above: A clean nest policy means you will spend much less time cleaning eggs.

Nest box hygiene is very important. Chickens allowed to sleep in their nest boxes at night will soil them. Collect waterfowl eggs on several occasions during the morning from clean bedding.

I keep only clean eggs for hatching and do not wash dirty eggs or wipe eggs clean with a damp cloth. I find it saves time in the long run and simplifies the whole procedure.

Washing removes the protective coating and exposes it to entry of bacteria. The washing and rubbing action can force pathogens through the pores of the shell.

I have tried both methods and have to admit that if done as per the instructions, cleaned and disinfected eggs are no different as far as hatch rate goes. Stick to what you know and prefer.

There are a few things to consider.

It is pointless cleaning and sterilising your eggs if you are then going to put them in an incubator that has not also had the same treatment. 

Remember incubators operate around 37.5 degrees Centigrade, the perfect temperature for bacteria to multiply.

Make sure your hands are clean, eggs without the bloom intact will become contaminated. If you handle the eggs with grubby fingers your reintroducing bacteria to the eggs.

Follow the instructions on the bottle. Sterilising agents are by their very nature strong chemicals and if the solution is too strong it could kill the embryo. If it is too weak it will not do it’s job. The shell gets very slippery when wet so be careful you don’t drop your eggs.

Do not put it down on a cardboard egg box to dry afterwards, use a clean plastic tray.

How to clean your eggs.

You need to have a basic understanding the role of the eggshell, it is one of nature’s great wonders. 

It stores calcium for the embryo to use for growth, conducts heat, allows water evaporation and also regulates respiration. It protects the internal contents of the egg against injury and contamination.

The eggshell has many pores which allow oxygen to enter the egg and carbon dioxide to exit. Eggs need to loose weight during incubation and water vapour also leaves the egg through the pores.

The cuticle, the outer layer of the eggshell is the first defence of an egg. It helps prevent water and contaminants from entering the pores.

Always keep the pointed end down. Pointing the blunt end down strains the membranes in the egg.

Dry cleaning using abrasives is an option for light soiled or eggs with a single mark on. You do run the risk of damage to the shell and blocking the pores. As with all cleaning methods it is time-consuming and weakens the cuticle. 

Dry cleaning does not work on eggs covered with faeces or the contents of broken eggs from the nest.

If you choose to use abrasives to clean the eggs remember to sanitise them from time to time in water with bleach and to allow them to dry before use.

Wet cleaning - Poor practices have given egg washing a bad name by creating more problems. 

Dirty eggs, covered with bacteria which will have trouble getting through the shell, so long as it remains dry. As soon as the shell is wet they pass through the shell. 

Clean soiled eggs using a brand egg wash solution such as Brinsea Incubation Disinfectant Concentrate. Follow the instructions on the bottle. Wash eggs in solution which is warmer than the egg otherwise dirty water will flow through the pores and contaminate the inside of the egg. If you cool the egg the contents shrink  causing a partial vacuum inside which tends to pull foreign matter into the egg. 

Wash eggs in a solution at 105°F / 41°C) and rinsed in another solution at the same temperature. Then set them in a clean dry rack and handled with clean hands.

Things to look out for when washing eggs:

If your washing solution is over 122°F / 50°C or immersed for too long can damage the embryo.

If the washing solution too cold, under 104°F / 40°C, it may pull some of the washing solution inside the egg damaging the embryo.

Do not make the mistake of over using the washing solution. Wash the cleanest eggs first leaving the dirty eggs for last. Change the solution rather than trying to add more disinfectant to an already dirty solution.

It is preferable to use washed hands to handle eggs.

The secrets to successful incubation are:

1. Clean and accurate equipment. I use a forced air incubator with both an electronic thermostat and a glass bulb thermometer to monitor temperature.

More than 1°C variation in temperature will badly effect a hatch and more than 2 or 3°C probably means nothing will hatch at all.  It has an automatic egg roller which can be put on a timer so it turns itself off on the correct day.

Hygiene is essential, clean eggs with no cracks to allow bacteria inside the egg and a clean incubator will improve hatch and survivability rates.

Clean , well chosen eggs with no cracks and good colour from healthy parents on a good diet. I would add that it is not a good idea to use small eggs from a pullet that is just coming into lay as they may have no yolk and small chicks will take longer to mature and grow. Very large eggs are not a good idea unless you are sure of the older hens fertility and have candled the egg to make sure it has only a single yolk.

Patience. A stable environment with the minimum of fluctuations in temperature and humidity is most likely to produce the best hatch rates. An electronic thermostat which can keep very accurate control of the temperature is a must, Adequate ventilation is important, the air inside the incubator should change gradually for fresh air.

The chicks inside the egg will still need to respire , oxygen passes through the porous shell and CO2 passed out. Make sure you leave the eggs and the incubator well alone during the first 10 days and resist the temptation to peek, the first 10 days is crucial and temperature fluctuations during this time are more likely to affect hatch rates. Eggs should be candled at day 10 and any clear eggs removed.

Don't forget to turn the egg roller on or to turn the eggs by hand and also to turn the roller of on day 18 or stop turning the eggs.

I add water at the correct temperature (38.1 °C) into the water tray to increase humidity for hatching. After temperature and hygiene, humidity is one of the biggest factors in hatch failure.

If the humidity is to high during the earlier stages of incubation the egg will not lose enough moisture and the chick will be to large to hatch successfully. If the humidity is to low the chick will be to dry to hatch easily.

Here in the UK I have never added water to the first stage of incubation, only at day 19 to assist with the hatch. i have always had very good hatch rates using this method, if you have a lot of big fully formed chicks dead in shell then to high a humidity is probably the cause.

If humidity is too low  they will struggle to emerge from the egg and may end up with large bits of shell or membrane stuck to them. An egg needs to lose approximately 13% of its mass during the 21 days of incubation, this helps to form the air space in the egg and to provide enough room for the chick to manoeuvre inside the egg before hatching.

Mark your eggs.

• A simple 1 or 2 will be fine. Or a line and a cross or circle.
• If you are the forgetful sort write something like 'morning' and 'afternoon' so you know which side should be facing upwards at which point in the day. 
• Or you might remember to do it after every meal.
• Add a date and breed if you need to know that information.
• Use and ordinary pencil, permanent markers have solvents.
• You should always add a mark to your eggs even if you have an automatic egg turner, it enables you to see at a glance that it is working.

Storing fertile chicken eggs.

Think like your chicken - A wild chicken will lay an egg a day into her choice of nest.  Sometimes twelve or even more. I had an white Orpington hen incubate a nest of 17 and only 1 did not hatch.

That means that the first one was at least 17 days old When she started sitting.

To the hen, incubating one at a time makes no sense and as she can only lay one each day, her eggs may be 12 or more days old before she begins to incubate them.

Plan ahead and have a regular hatching schedule to avoid storage problems. 

Many times people attend to the incubation process but disregard the care of the eggs before they are set. Even before incubation starts the embryo is alive and needs proper care. You will get reduced hatchability if the eggs are not cared for. 

Collect eggs at least every day and three times a day in hot weather.

Store eggs in a cool and humid storage area. Ideal storage conditions are 45 - 55 degree F or 7 to 12 Centigrade. 

Do not store them in your refrigerator. It is too cold and the air is much too dry. They will lose moisture through the shell if they are small eggs like bantams or have thin or porous shells.

Make use of the correct size of storage containers so the eggs are not rattling around.

Store the eggs with the small end pointed downward even if it's only for a short time.  This makes sure the yolk stays suspended and this is the way they should be set in the incubator. If the more rounded end faces downwards for too long there's a danger that the air cell will become dislodged and the developing embryo will die.

Alter egg position at least once a day if not incubating on the day. Turn the eggs to a new position once daily until placing in the incubator. If you're storing your fertile eggs on there side in containers all you need to do is turn the whole box upside down. There is no need to turn them one at a time.  Make sure you mark the container so you know which side is which. You can keep them in a tray and tilt it backwards and forwards.

Remember when turning eggs:

If they are on their side turn them backwards then forwards, never turn the same way over and over.

Pointy end down, tilt backwards and forwards past the 45 Degree point.

The yolk contains fats and will try to float to the top of the egg where it will stick to the membranes and cause development faults and aborted embryo’s.

Experience and laboratory trials have shown that storing and incubating fertile eggs them the wrong way up will result in few, if any, hatching.

Eggs contaminated with oils from the skin or other sources suffer from reduced gaseous exchange. This means the embryo may struggle to breathe.

Take extra precautions when turning eggs during the first week of incubation. The developing embryos have delicate blood vessels that rupture when jarred.

A hen will keep her eggs lying sideways, I use this method and it works fine.

Hatch-ability holds up well to seven days, but declines afterwards. At 21 days there is no chance of a viable embryo. I have found posting reduces this time by at least half.

Natural incubation with hens:

The aim is to reproduce the way a hen will instinctively behave until she is ready to settle down and start incubating. Using a broody hen is by far the best way of raising chicks. the hens hold the perfect temperature and humidity and watching them turn eggs is fascinating.

The procedure for the selection of eggs is the same but setting is slightly different. it is unwise to set more than 10 or 12 eggs even under a large hen. The eggs should be set at night and carefully so as not to disturb the hen, under cover of complete darkness slip the eggs under the hen, she will adjust their position on her own.

Here are some pointers, learned from reading about chickens and watching how my own hens keep their eggs.

You can not force broodiness in a hen but you can provide the ideal conditions.

Find a quiet spot. Disturbed hens will leave the nest and broodies often do not mix with the rest of the flock. If they are blocking another hens favourite nest box there will be much squabbling.

You need to do nothing more than make sure she is fed and watered and gets of the nest for a few minutes a day to eat, drink and defecate. She will let you know when the hatch is imminent as she will rumble to the chicks in encouragement.

Below: Cat boxes make excellent broody nests. Easy to move and clean. 

This Double Laced Barnevelder is happy in her box.

She will need to feel secure in an dark nest box with one opening.

Some breeds are more broody than others, I have some Barnevelder cross Slkie bantams that would raise clutch after clutch regardless of the time of year. Put them in a brood pen with a nest of eggs and they settle in a day or so.

Do not use a dirty nest box and dust it well with diatomaceous earth before the bird sets on her eggs. One of the most critical issues for hatching is to make sure the eggs don't become contaminated with bacteria.  By choice a hen will use a quiet, clean place to set her clutch.

Use the same rigorous selection and storage procedures for eggs as you would do if you were using an incubator.

She knows instinctively that she has to prevent the embryo sticking to the membrane inside the shell and will turn her eggs into the centre of the nest. 

Let her do her thing. It is rare than hens are crap mothers although it does happen.

Make sure she has feed and water and leaves the nest for 20 to 30 minutes a day. I do this in the early evening when my other birds have roosted so it is quieter and undisturbed.

It is relatively easy to tell a broody hen, they have a very different behaviour to laying hens. They sit very flat on the nest and will defend the nest with violent pecking and a low rumbling growling noise or a sort of open beaked squeaky hiss.

It also seems to cause some disruption to the rest of the flock, as the birds tend to have a favourite nest and don't like to find another bird sat on their spot. The other hens also seem to pick on broodies. You will need to watch your fingers around a broody hen, they are much more bold than an average chicken and will peck which can hurt.

We have 1 hen that is almost permanently broody, we found her trying to brood 3 golf balls in a flower pot. Such hens are very useful as she will raise brood after brood during the year. They do require some special care as they can neglect their own needs whilst sitting on eggs and being sat on eggs for 21 days can make them susceptible to parasites.

The artificial Incubator.

At its most basic it is a box with an artificial warm and humid environment. You can buy one or make your own and they come at virtually every price point.

The size and type of incubator you select depends on your needs and future plans. Many different models are available and each  one is different and has a different duty cycle. I have used a great many over the years and some are much better than others.

Below: Brinsea Octagons have stood the test of time. 

The brinsea method is to turn the whole device on a cradle whereas some others have plastic or metal egg rollers and some have rollers which slowly turn the eggs. All these methods work just fine and your choice will be a matter of personal preference.

For continuous settings a separate incubator and hatcher unit is a good idea.  If all eggs are at the same stage of incubation use a single unit as both incubator and hatcher. 

Locate the incubator and hatcher units indoors to protect them from weather and climate fluctuations. 

Choose a room has a good ventilation system to supply plenty of fresh air. Keeping the units indoors makes it easier to maintain uniform temperature and humidity. 

There are two types of incubators available, forced-air and still-air incubators. 

Below: This is one of my four Chicktec incubators, it has run continuously for 6 years.

Forced-air incubators have fans that provide internal air circulation. The capacity of these units may be very large. The temperature is lower at 100 °F or 37.78 °C

The still-air incubators tend to be smaller without fans for air circulation. Air is exchanged by the rise and escape of warm, stale air and the entry of cooler fresh air near the base of the incubator. The recommended temperature is 101 °F or 38.3 °C and careful setting ensures this is maintained at the level of the egg centres.

The five incubation temperature zones:

Research carried out by scientists identified five temperature zones. They are defined by the effect on the developing embryo. 

You cannot effect the gender bias of your hatch by adjusting the temperature. I have run into this so many times it is giving me a headache. the Sex of a chick is fixed at the fertilisation of the egg cell. Hens are more likely to survive high temperature than Cockerels. If there was any benefit in incubating at a different temperature the commercial hatcheries would be doing it.

Zone of heat injury: 

At continuous temperatures above 40.5°C (104.9°F) no embryos will hatch. Short periods of high temperature are not lethal. Embryos up to 6 days are particularly susceptible, older embryos are more tolerant.
 
Zone of hatching:

Within this range there is the possibility of eggs hatching. The best is 37.8 °C or 100.4°F. Above this temperature hatches will be reduced and the number of unhealthy and deformed chicks will increase.

Continuous temperatures within this range but below 100°F slow development and increase mortality. It is evident that early embryos are more susceptible to continuous low temperatures than older embryos.

Zone of disproportionate development: 

Eggs kept above 27°C (80.6°F) will start to develop but some parts of the embryo will develop faster than others and some organs may not develop at all. Below 35°C (95°F) no embryo is likely to survive to hatch. The heart is much enlarged and the head development more advanced than the trunk and limbs.

The temperature at the lower end of this range is sometimes referred to as Physiological zero. This is the threshold temperature for embryonic development. Unfortunately different organs appear to have different thresholds resulting in an unviable embryo.

Zone of suspended development: 

Below 27°C (80°F) no embryonic development takes place. Before incubation store eggs in this temperature range around 7 to 10 °C/44 to 50°F). 

Zone of cold injury: 

Below -2°C/28.4°F ice crystals will start to form in the egg splitting membranes and damaging internal structures. Eggs may lie for some considerable time in temperatures close to freezing without suffering damage.

Incubating Conditions

Maintain a still-air incubator at 101 °F to compensate for the temperature layering within the incubator.  Obtain the proper temperature reading by setting the bulb of the thermometer to the same height as the centre line of the eggs. Incorrect readings will result if you allow the thermometer's bulb to touch the eggs or incubator . 

Check your thermometer. Is it accurate? An error of one degree for 21 days can interfere with embryonic growth. Check the accuracy by placing the bulb next to the bulb of a medical or laboratory thermometer. Place both in a beaker of warm water and compare the readings. A split or gaped mercury column will not give an accurate reading so get a new one.

1. Stable temperature - 100°F / 37.7°C for forced air or 101°F / 37.9°C for still air machines.
2. Stable humidity – Ideally 55% for incubation and 65% for hatching. Stability is more important than actual levels.
3. Ventilation – You must have a steady flow of air or they will suffocate.

Do yourself a real favour and do not buy a digital temperature probe. Buy a quality glass medical or laboratory thermometer.

The importance of turning eggs

In broody hens the brood patch provides heat from one direction and the eggs at the side of the patch are cooler than those in the middle of the nest. The hen turns and moves the eggs in the nest achieving uniform egg temperature.

Egg turning prevents adhesion of the embryo to the inner shell membranes and stimulates the rate of development of the area vasculosa. This is the membrane which grows around the yolk and is rich in blood vessels. The area vasculosa is important for sub-embryonic fluid formation and for yolk uptake later in incubation.

It allows for circulation and transfer of albumen proteins into the amniotic fluid and supports the growth of the chorio-allantois, the blood vessels right under the shell, which maximise oxygen absorption and allow calcium transfer.

Embryos in unturned eggs grow at a lower rate compared to embryos in eggs turned each hour over 90°.

Egg turning facilitates movements of the embryo into the normal hatching position and reduces the incidence of malpositions in unhatched embryos.

The most critical period for turning hatching eggs is during the first week of incubation. Absence of turning between 0 and 2 days increased early mortality versus 3 to 8 days which increased late mortality.

The effect of not turning during the first half of incubation is only seen during the second half of incubation, but by then it is too late to take corrective actions.

Turning failures during the second half of incubation will generally have less dramatic effects, although the growth rate of the embryo can be affected, depending on the moment and duration of the turning failure.

The angle through which the eggs turn is important. Hatch of fertile eggs was better in eggs turned over an angle of 45° either side of the short axis of the egg, as compared to turning of 30° and 15°. Hatched chicks from eggs turned 45° weighed more and had less dry matter in the residual yolk. (Cutchin et al, 2007)

Points to note:

•    Make sure that turning does not produce shocks or jolts, as this affects hatch-ability and chick quality.
•    If necessary, check and adjust the turning angle: 45 to 50° is optimal.
•    It is advisable not turning for the first 12 hours. Eggs are best left for this period to come to temperature and to restore their internal balance.
•    Turning is not necessary after 15 days of incubation but should continue until day 17. After this eggs should be in a horizontal position for hatching for stability and increased air flow.

Manual turning the eggs in your incubator:

If you do not have an automatic turner you should turn your eggs about 3-5 times per day from the second day onward. You should not turn your egg after Day 17 which is two - three days before the chick will hatch. This will give the chick time to position itself for hatching.

If you have marked your egg with an X on one side you can tell if you have turned your egg or not. 

Remove the lid of the incubator for the shortest time you can. Do not rush and make sure you turn the egg without jarring them. 

The temperature and humidity of the incubator will drop but it will soon recover its temperature. This is another good reason to leave well alone after day 17, hatching requires stable humidity.

An unfertilised egg will lose heat quicker while a fertilised egg will not. This is how a hen know which eggs to throw out of the nest.

When you turn the eggs by hand, wash your hands to avoid transferring bacteria and oil onto the surface of the egg.

Humidity is relative

Why have I left the discussion on humidity until now. I know I am going to cause a stir with this but it is actually less important than most people make out.

It is much more important that the humidity level is stable in the incubator rather than it’s actual reading.

graph of humidity % during incubation

There is much confusion about the measurement of humidity. Accurate measurement is as difficult. The readings are less accurate as humidity tends to either extreme and more accurate around 50%. My experience is that novice and seasoned poultry keepers make a lot of mistakes around humidity.

Do yourself a solid favour and avoid electronic humidity readers. get a good quality analogue one.

Correct humidity prevents unnecessary loss of egg moisture. Too low and the chicks will hatch small and weak.
The converse is also true, the egg needs to lose enough moisture to enable the hatch. Too high and it will not lose enough mass to hatch.

Relative humidity in the incubator between setting and three days before hatching should remain at or close to 55%. When hatching the humidity increases to 65% relative humidity or more.

I will say it again – Stable humidity is more important then the actual reading. In my experience the humidity is low in ventilated incubators.

The water pan area should be equal to at least half the floor surface area and split for control. 

Increased ventilation during the last few days of incubation and hatching may need the addition of another pan of water or a wet sponge. Maintain humidity by increasing the exposed water surface area not by cutting ventilation. 

An excellent method to determine correct humidity is to candle the eggs at various stages of incubation. 

This is the normal size of the air cell after 7, 14, and 18 days of incubation for a chicken egg. 

Adjust humidity after candling  and weighing. The egg's weight must decrease by 12% during incubation for good hatches.

The embryos are moving into hatching position and need no turning. Keep the incubator closed during hatching to maintain proper temperature and humidity. The air vents should be open full during the latter stages of hatching.

What if the electricity goes off during incubation?

Cooling is a natural process as most birds will get off the nest at least once a day and leave the eggs unheated for a significant time. It is a surprising fact that although eggs must have very stable temperatures to incubate successfully.

I have had several power cuts during incubation and can say that if you are quick you can get away with outages as long as 8 hours. With the help of a hot water bottle and a few layers of bubble wrap it is easy to keep the eggs from chilling.

Unnoticed power cuts limit you to about 5 hours. It depends on the stage you have reached.

A proper response depends on several factors, some of which include the temperature of the room in which the incubator is located, the number of eggs in the machine, and whether the eggs are in the early or late stage of incubation. 

Lots of eggs in an advanced stage in a well insulated machine will stay warm quite a while. Eggs produce their own heat with cell respiration.

If power loss occurs when the eggs are near hatching, incubator temperature is less critical, but severe chilling will cause mortalities. It is preferable to limit heat loss by keeping the incubator shut and raising the temperature of the room if possible. The metabolic heat from the embryos will keep them warm for quite a long time.
 
Avoid subjecting the eggs to  high temperature, above 103 F at any time. Incubator thermometer readings will not be the same as embryo temperatures when cooling or heating occurs. The eggs will lag behind the air temperature. For example, cooling hen eggs by taking them out of the incubator into a room at 20°C/68°F for 30-40 minutes is likely to cool the internal egg temperature by only 3 - 5°C (7 - 10°F). Eggs smaller or larger than hens eggs will react quicker or slower.

Trouble Shooting Failures

Novice and experienced poultry producer alike will encounter problems when incubating. The causes of failures can be diagnosed.

A forced air incubator that is too warm tends to produce early hatches.

One that runs cooler tends to produce late hatches. In both cases the total chicks hatched will be reduced.

Day 0 to 21. What's going on behind the shell?

Images and video of the stages of incubation of the chicken egg.

The egg is a unique method of reproduction, it provides all the nutrients and protects the embryo to allow it to develop. It is also a self contained study package being easy to get hold of and reliable in producing results.

The ovum from the hen and the semen from the males are produced by a cell division process called Meiosis where each end up with half of the chromosomes needed to produce and offspring.

Above: Successful incubation starts with clean eggs from suitable parents.

During incubation, the embryo develops in a predictable manner with specific events occurring at specific times.

To develop, the embryo must have a way to receive nutrients from the egg. The embryo develops extra-embryonic membranes for this function. The extra-embryonic membranes are the yolk sac, the amnion, and the chorio-allantoic membrane.

The yolk sac is a membrane that spreads over the yolk and transports food from the yolk to the embryo. The amnion is a fluid-filled sac that covers the embryo and protects it from physical shocks and injury.

The chorio-allantoic membrane has four functions:

1. It is a respiratory organ that provides oxygen to the embryo.
2. It is a storage area for the waste products the embryo produces.
3. It provides food from the albumen to the embryo.
4. It brings calcium from the egg shell to the embryo.

The development of an embryo is a fragile process that is easy to disturb.

A list of common incubation problems and their causes is below - link - You can prevent many of these problems by maintaining proper temperature, humidity, ventilation, and by regular egg turning.

Day 0 – Why have I included day zero? Well 4.5 % of the development of the embryo in a chicken happens before it is even laid. After fertilisation, the embryo begins to grow by cell division (Mitosis) . By the time the egg is laid, the initial single cell has developed into 4,000 to 6,000 cells and looks like a small doughnut.

Once laid the embryo will remain at rest for a viable period, up to 14 days in chickens.
Physiological zero is 68°F/20°C. Below this all development ceases. The ideal incubation temperature of the chicken is 99°F-100°F (37°C-38°C). If the temperature of the egg goes above physiological zero, embryonic development can occur. Above physiological zero but below optimal incubation temperatures will result in weaker embryos and higher mortality. Parts form at different rates and result in some odd deformities at hatching or autopsy time.

Day 1 – Under the right condition you can see the development of the embryo 24 hours after setting. It is a large circle with a dot in the middle and is more of a shadow than real definition. It is a larger version of what you see on an unincubated egg.

Above: Day 1 and you can make out a dot and a circle show as a shadow.

The Blastoderm appears as doughnut shaped ring.  Area pellucid and area opaca.

An infertile germinal disc appears as an undefined mass. Alimentary tract appears after eighteen hours and the central brain crease an hour or two later.The head, brain and nervous system as well as the vertebral column appear before 24 hours is up. Blood islands appear and the beginning of formation of eyes.

Day 2 –  By day 2 there is blood visible in tiny vessels and it is beginning to look like a spider. The limb buds are beginning to form.

Above: Day 2 of incubation and the ring clearly defined and blood beginning to show

Day 3 – The yolk begin to spread out and the membranes stretch out. The yolk begins to look like a half empty sack. this has the advantage of increasing its surface area. The heartbeat is visible. Vascular system well developed.

Below: Day 3 and development is clear to see.

Left side of embryo on yolk. Wings and allantois form. Amnion surrounds embryo and leg and wing buds begin as swellings.

Day 4 – Movement can be seen from day 4 with the right shell and a bright enough light. The embryo itself is about the size of half a peanut. The limb buds have formed and the eyes are becoming pigmented. Increase in size of brain and heart. Limb buds approximately as long as they are wide. Legs longer.

On thing static pictures do not show is how much movement happens within the egg. And how important turning the eggs is to keep the membranes from sticking.

Day 5 – The beak is becoming visible and the embryo almost looks like a small chick. The limbs are now identifiable  and the black dot is the eye. limb buds longer than wide. Allantois breaks through amnion.

Above: Day 5 in the incubator and blood vessels have spread over most of the membrane surfaces.

Day 6 – On day 6 of incubation the blood vessels have spread well around the egg and the embryo looks like a eye dot. It is the eye that shows as the black dot and the embryo looks like a large baked bean. The egg tooth is visible on the tip of the beak. Voluntary movement begins.

Above: Day 6 and the eye dot is more defined.

Day 7 – The surface area of the yolk sac has increased to its fullest extent. Most nutrients are absorbed from the albumen but also from the yolk and shell. Gaseous exchange requires a large surface area. The comb begins to show.

Day 8 – As the chick grows the veins become a bit washed out. and the shadows begin to get larger. The feather follicles show and down pins are visible. Feet and wings well developed, down formations starts, nictitating membrane starting to cover eye.

Day 9 – Mouth opening appears. large egg tooth, eyelids extend toward beak and start to overgrow eyeball.

Above: Day 9 of incubation and the embryo is clearly visible.

Day 10 – The beak begins to harden. Comb appears as a prominent ridge.

Above: Day 10 and regular movement can be seen.

Day 11 – Tail feather begin to appear . Proportions of head and body changing.

Above: Day 11. The body begins to catch up with the outsized head.

Day 12 – Toes and limbs fully formed. Chick continues to grow.

Above: Day 12.

Day 13 – Leg scales and claws visible. Embryo almost completely formed.

Day 14 – Eyelids and eyes have formed including the nictitating membrane or third eyelid. Embryo turns toward the blunt end of the egg.

Above: Day 14 and the embryo is beginning to fill the space. you can also see the air sac getting bigger.

Day 15 – By day 15 of incubation the development is more or less complete. the yolk almost surrounds the chick completely. The down is complete and the extremities formed . Small intestines taken into the abdomen. increased size and down.

Day 16 – As the chick grows the yolk absorbs into the chick in preparation for hatching.

Day 17 – There is only a little free space left in the egg, as seen near the air space. The embryo rotates to final hatching position with the head under the right wing pointing toward the air cell. Amniotic fluid absorbed.

Day 18 -- By day 18, the embryo has developed into a chick and will take up most of the space in the egg. The chick is preparing to hatch. You can do a few things to best help the chick prepare:

Stop egg-turning at day 18 with the larger end of the egg facing up or the egg laying flat as it would do in the nest. At this point, the chick will position itself for hatching inside the egg.

Day 19 –. Absorption of allantoic fluid completed, yolk sac about half enclosed by body.

Day 20 -- The yolk finished absorption into the chick. This is what makes it possible for hatchlings to be able to survive without food or water for several days.  

Yolk sac completely drawn into body cavity and umbilicus closing over; inner shell membrane pierced, piping begins, embryo breaks (internal pipping) into air cell and breathing begins; allantois ceases to function and starts to dry up.

Above: Air cell from the chicks side. It gets bigger as the egg loses water during incubation.

The egg tooth on the beak is poised to start pushing through the shell and, apart from the air cell, the embryo is completely filling the egg. The shape of the egg makes it strong from the outside but easy to get out of

The egg tooth starts to penetrate the membrane, the lungs are working and breathe in that all-important air from the air cell.
It's at this point that you may start to see a hole in the shell as the chick begins to break through with its egg tooth - which will fall of a couple of days after hatching.

Day 21 – This is for the most part is hatch day and you should be going from pip to chick. If you have got your temperatures and timing correct the bulk of the chicks should hatch within the next 24 hours. Some chicks hold on and don't hatch exactly on time and seem to spend ages wiggling their beak in the pip hole. Do not worry about this and best not to interfere and try to open the shell.   Doing so before the yolk is completely absorbed will kill the embryo and result in a guilty mess in the incubator.

The blood from the vessels inside the eggshell withdraws into the chick and the final hatch begins when this is complete.
If all is going to plan, the chick now begins to breakthrough.  It uses its wing as a guide and its legs to push it and works in a circular pattern to create a hole. This process is called unzipping and results in the eggs splitting into two.

It's a tiring process and there will be a lot of rest periods before it finally hatches.  The average length of time between pipping and chick hatching is between twelve and eighteen hours - in some cases longer. It needs to spend a lot of time catching its breath and working its little lungs to build its strength.

Dark shelled eggs:

Dark shelled eggs (Marans, Barnevelders or Welsummers) are much harder to see through even with a very bright light. You need the best light source you can get but it should not be to hot as you do not want to injure the chick.

Candle the eggs in a dark room or cardboard box to stand a chance of seeing inside the shell. The best you are likely to see is shadows and you will have to wait longer until the embryo has developed further and can be more easily seen. 

Hatching

The Hatching process starts about day 19 when the chicks break through the internal membrane into the airspace inside the shell. It is at this point you can hear the chick peeping inside the shell if you listen carefully. Within a few hours a small triangular hole will appear, generally in the upper part of the shell.

This is made by a small tooth on the upper end point of the chicks beak and is so the chick can breathe properly. This is called pipping and results in a little triangle of shell popping up generally on the upper half of the egg. The chick may well spend as much as 36 hours like this before beginning to break out of it's shell.

When the hatching itself begins the blood begins to withdraw from the membrane inside the shell and the chick gradually begins to force its way out of the shell by enlarging the pipping hole into a crack.

With a few final pushes it will break the shell in half and flop out. The chicks are unable to stand properly to start of with and seem to drift in and out of sleep for a few hours. They will dry out and brighten up quite quickly and become very active in about 8 hours.

Below: A hatching egg in the process of unzipping.

Below: A newly hatched chick. They should be left in the incubator until they are dry and fluffy.

They question of weather or not to help at a hatch is a very difficult one. As a rule I tend not to help at a hatch. If the chick was not ready and you try to remove the shell, it may bleed to death or you may damage the chick.

If the chick is struggling you can give some gentle assistance, Gently move the shell to add some pressure to the two halves to see if they give easily to release the chick.

If a blood spot appears then leave well alone. It is quite common for some membrane to stick to the chick and this can prevent it hatching properly or weaken it considerably.

To deal with this you will need some warm water and a cotton bud, just moisten the spot where the membrane has stuck, leave for a few seconds and then use the cotton bud to loosen the membrane.

Drying and transferring to the brooder.

How long the chick should stay in the incubator is a matter of personal judgement. I leave mine a full 24 hours after hatching. I also do not help chicks to hatch.

These chicks that hatched at the same time were more than happy to rest and sleep. 

There is enough resources in the yolk to sustain a chick for 72 hours at least so do not worry, a night in the incubator will not do them any harm.

So resist the temptation to open the incubator too soon.  The chicks will be fine in there for 72 hours

When chicks emerge they stumble around the incubator not able to keep control of their legs. They knock into other eggs which have not yet finished hatching. There is evidence that hatchlings encourage the rest to hatch, in particular with their peeping.

When they first hatch they are wet and there are periods of deep sleep where consciousness seems to come and go. You must leave them until they are up and about and dry. Pipping, unzipping and hatching takes an enormous amount of energy.

When is it safe to open the lid of the egg incubator to move the chicks?

Your eggs should all pip within 24 hours of each other and at most a hatch should not take more than 36 hours. If it does not then your settings are wrong or the eggs have not been chosen correctly. It is safe to open up when you are sure that no more chicks are hatching. opening the incubator at that point will cause humidity to drop immediately which can dry out the membrane of any chicks who have begun to pip.

Part of the selection process involves choosing eggs that hatch at the same time. The hens do it. They leave eggs in the nest ensuring the 21 day cycle through to the next generation. Allowing late hatches will leave you with a strain of chickens were the eggs hatch at 23 days.

Chicks can chill fast. Move to a brooder that is at temperature. 

A dried out membrane means the chick will not emerge without help.  The membrane becomes very leathery and stiff rather than pliable and the chick will not be able to break through it. When the membranes are moist and pliable the chick is able to tear them.

At best this means you will have to assist it in hatching.  At worst it will mean that the chick will die in the egg. This shrink wrapping of chicks can happen fast. Taking the lid off the incubator is enough.

Incubation and hatching Frequently Asked Questions FAQ's :

What about food and water for the hatch-lings?

Chicks are fine without either for up to 72 hours. This is how hatcheries are able to ship day old chicks.  The yolk, absorbed during the last phase of incubation, will nourish the chick for all that time.

Do not add food and water to the incubator. Have it ready in the brooder.

What about a chick who can not seem to get dry?

As chicks hatch the humidity in the incubator rises and those that have already hatched find it difficult to dry off. 

There is no choice, the chick will be warm in the incubator and will dry off. Be patient.

What if I have to open the incubator?

Deal with it according to each individual situation.  I open the incubator from one side enough to get my hand in. Remove the chick and at the same time add kitchen paper soaked in warm water into the incubator.  This raises the humidity level again for the unhatched chicks. Decide for yourself.