How to Tell if an Egg Is Fertilized
There are various occasions when you might need to know if an egg is fertilized. Generally speaking, they fall under two main categories. The first is if you have a bird or a reptile as a pet. In these cases, it is possible they will lay an egg at some point and you will want to know if it has been fertilized. The second is if you come across an egg in the wild. You might want to try to return a fertilized egg or even want to incubate them yourself.
Just because an animal lays an egg, does not mean it has been fertilized. In fact, the chances are pretty slim if you have a female animal with no males around. To be sure, AnimalWised explains how to tell if an egg is fertilized. We do this by using something known as the candling test for eggs.
Before performing the candling test
If you stumble across eggs in the wild, it is best to leave them alone. The parent may be close by gathering food and disturbing them can have seriously negative effects. For domestic animals, you will need to remove eggs form their housing. This is because they will rot over time and provide a hygiene hazard, in addition to providing a very unpleasant odor.
We should be aware of whether there are any males in the enclosure or that may have access to it. Although we should have all the information we can before adopting an animal, it can be difficult to tell the sex of some birds and reptiles. Laying an egg might be a surprise if you thought a female was a male. Only if the animal has access to a potential mate will the egg be fertilized.
Before performing the test, we must wait a few days until the eggs have incubated a little. In the case of chickens, we must wait about seven days. If we perform the test before a few days of incubation have passed, we won't be able to know the result with certainty. If we observe the hen isn't incubating the eggs, we can discard them. They will not be fertile without a male and even fertilized eggs won't hatch if they are not incubated properly.
Testing whether an egg is fertilized should not be done every day. Manipulating the eggs too much can harm their development and can even anger the mother. If she is scared, she may destroy her eggs rather than let them be eaten. The chance of this happening will depend on the animal species. Another problem is that testing them too much can interfere with the incubation by changing the temperature too much.
We explain more about the fertilization process of chickens with our article asking how often do hens lay eggs?
How to tell if a bird egg is fertilized
The candling test can be used to tell if a bird egg is fertilized. It involves shining a bright light on the egg so a strong bean passes through, allowing you to see what's inside the shell and verify its condition. To perform the candling test and determine the fertility of the eggs, you must be in a completely dark place. Turn off all the lights and even make sure no light is coming in through the windows.
To perform the candling test on eggs, you will simply need a suitable light source. A string flashlight is ideal, but you can even use a candle if the flame is strong and the environment is dark enough. There are even specialized egg scopes which use the same basic technology, but also hold the egg in place and make it easier overall.
If we use an egg scope, we'll just need to place the egg properly in the egg holder and secure the cover. You can then look into the viewfinder and switch it on. This will illuminate the egg in complete darkness and best let us see what is inside.
When using a flashlight, we'll need to wrap our fingers around the beam and hold the egg inside. We prevent the light from escaping between our fingers and focus all the light through the egg. In the case of bird eggs, we can focus the light from any point on the egg we want. We can rotate it to find the angle that best illuminates the interior.
When we have adequately illuminated the egg we will be able to observe for the following:
- Fertilization of the egg
- Cracks in the shell
- Stage of embryo development
- Signs of mortality
To tell if the bird egg is fertilized, we should look to see if we see a dark spot from which small veins emerge in the form of a spider web. These represent the center of the embryo and the developing blood vessels. This tells us that the egg is indeed fertilized and an embryo is developing inside the shell. If we're not sure, we can let the egg continue incubating and wait for the next test in a week to fully confirm fertility.
We might observe that the egg is uniform and there is an absence of spots and blood vessels. In this case, the egg is infertile. If this is the first test we've performed on an egg that looks like this, we can still leave it and wait for the next test to verify that there hasn't been any delayed development.
In the second test we perform, we may notice an egg that was developing the first time we examined it has stopped developing. This is due to various reasons, such as genetic problems, temperature changes, inadequate humidity or bacterial infection. In the first test we perform, we should note if we see any cracks in the eggshell, no matter how small. This will show that we need to be particularly careful and not presume it will hatch.
During this second examination, we may notice the appearance of a ring of blood with a distinct red circle. This is a very reliable indicator that the egg has stopped developing. Another way to indicate that the embryo is no longer developing is to see various blood spots, although this is sometimes difficult to distinguish from an early embryo. In these cases, we can let the egg continue incubating.
It would be a good idea to count the eggs and take notes on what is observed with each. This way we can compare the results in the next test we do and better monitor their development. We can keep the eggs out of the nest or incubator for a maximum of 20 or 30 minutes to ensure that the embryos' development has not been affected. Birds often leave the nest for a few brief minutes, but we must be very careful not to overstay our welcome to prevent them from stopping their incubation.
In addition to how often chickens lay eggs and how long they incubate, you may want to know how many eggs does a hen usually lay?
How to tell if a reptile egg is fertilized
The gestation period for reptiles is generally longer than that of birds. Therefore, we should wait between 15 and 21 days to perform the first candling test for reptile eggs.
Another very important difference is that reptiles are much more sensitive to temperature during incubation. We must carefully monitor the temperature and ensure the test site is at a similar temperature to the nest or incubator.
Depending on the size of the nest and the number of eggs present, the temperature may vary by a few degrees from one part to another. This is why the eggs will have different temperatures depending on whether they are on the surface or the bottom. These small temperature differences are one of the factors that determines the sex of the embryo.
It is vital for the development of a reptile embryo that the egg always be in the same position. When we handle a reptile egg, we must try to keep it in the same direction we found it, vertically or horizontally. Never turn a reptile egg over. To be sure, we can make a mark on the surface of the egg facing upwards with a special marker. We can perform the candling test with the egg in that position and place it back in the exact same place. If we don't do this and turn the egg over, the embryo can suffer various damages and even die. Its really worth taking our time and doing it slowly and well.
Learn more about reptile fertilization with our article asking do iguanas lay eggs?
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