Eggs can fail to hatch for a variety of reasons: infertility, environmental conditions like weather or chemical use, or physical damage to the eggshell.
Hatchability will decrease if eggs are handled poorly or get too hot or too cold in transit. Fertile eggs must be collected carefully and stored properly until they are incubated. Keeping the eggs at proper storage temperatures keeps the embryo from starting and stopping development, which increases embryo mortality.
Poor results in hatching are commonly caused by the improper control of temperature or humidity. When the temperature or humidity is too high or too low for a long period of time, the normal growth and development of the embryo is affected.
If there are still unhatched eggs at day 21, don't despair. It is possible that timing or temperature went slightly awry, so give the eggs until Day 23. Candle any unhatched eggs to see if they are still alive before discarding them. Keep in mind that when hatching eggs, you will likely end up with roosters.
If the humidity is allowed to decrease after the chick pips the shell, the membranes within the shell can dry-out and stick to the chick. This prevents the chick from turning inside the shell and stops the hatching process. The chick eventually dies.
The average length of time between pipping and chick hatching is between twelve and eighteen hours - in some cases longer. Again - don't worry. Let nature take its course.
It is reasonable to expect a chick to hatch within 12-24 hours of pipping. Egg #1 certainly wasted no time at all from pip to hatch, breaking free in less than 12 hours.
The longest incubation was recorded in the case of an egg of the mallee fowl (Leipoa ocellata), Australia, which took 90 days to hatch, compared with its normal 62 days.
“First, for the Day 22 and no hatching chicks situation, it certainly does no harm to leave the eggs alone for another day,” he says. “They possibly could hatch, although it's fairly unusual for eggs to hatch and produce healthy chicks after Day 23.
Bigger eggs need more total incubation time, as at the same egg shell temperature the embryo will grow at more or less the same rate, but as there are more grams of egg and grams of final chick, it will take longer to hatch.
The process of removing dead eggs while incubation is called 'Candling'. It involves shining a bright flashlight through the egg in a dark room. Upon close inspection, you'll see veins running through the egg in case it's alive.
And remember, all of this is based upon the assumption that these farmers have roosters around. Hens lay eggs with our without a rooster present. Without a rooster to fertilize the egg, it will never become a chick.
Below about 27°C (80°F) no embryonic development takes place. Prior to incubation, eggs must be stored in this temperature range, ideally around 15°C/59°F. Below this threshold ice crystals will start to form in the egg and permanently damage may be done to internal structures meaning the egg cannot hatch.
Chicken eggs should hatch 21 days after they first start in an incubator. (Remember that your eggs have already been incubated for 14 days before you receive them!) Other bird species have different incubation times. For instance, duck eggs take 28 days to hatch; goose eggs take 30 days.
Various things will influence hatch times: the age of the eggs, the health of the mother hen, fluctuations in the incubator temperature... Sometimes chicks hatch a little before 21 days, sometimes it can be several days after. Don't give up on your chicks until 26 days have passed since they were set.
While I can expect to hear cheeping from within the eggs at any time now, it is most commonly heard around day 20. Chicks can hatch earlier or later than day 21 depending on whether temperatures were off a little bit one way or the other (too cool and they'll hatch later, too warm and they'll hatch earlier).
A hatchability of 80 percent (of eggs set) from natural incubation is normal, but a range of 75 to 80 percent is considered satisfactory.
If you use an egg from a young pullet that is too small in size, the chick may not have enough room to grow and develop properly. It may not hatch, or if it does hatch, the chick could be weak. So, when it comes to choosing eggs to use for hatching, you always want to use eggs that are regular in size.
Several interrelationships are apparent between egg weight, chick weight, chick growth and other parameters. The hatchability of intermediate size eggs is better than that of very large or very small eggs.
Some novice poultry keepers get nervous after seeing a pip hole and no progress. Don't panic, BE PATIENT! You can harm the chick if you interfere with the natural process and start to pick at the shell. The time between a pip hole and final hatching can easily be 12 to 24 hours.
It's likely that the chick will just hatch a little later. I have had chicks hatch as late as day 26, so don't despair. And do not be tempted to "help" the chick out of the egg. Nature will take its course, and trying to remove the shell before the chick is ready is more likely to kill it.
Sometimes eggs found outside the nest are viable and sometimes she continues to sit on rotten eggs until the bitter end. I wish I had a nickel for every rotten egg I have discovered in the nest after a hen has left it to care for her brood.