How Do You Tell the Difference Between Fertilized and Unfertilized Eggs: A Simple Guide

Have you ever wondered how to tell the difference between fertilized and unfertilized eggs? It can be a bit tricky, especially if you’re not an expert in the field of poultry. Luckily, with just a bit of knowledge and a keen eye, you can discern the difference in no time at all. Whether you’re a home cook looking to whip up some egg-centric recipes or a farmer trying to maximize your egg output, it’s important to be able to differentiate between fertilized and unfertilized eggs.

So, what’s the difference between fertilized and unfertilized eggs? Well, fertilized eggs contain an embryo that will eventually hatch into a chick if the egg is given the right conditions. Unfertilized eggs, on the other hand, are simply eggs that have been laid without the presence of sperm. While fertilized eggs are often sold as a delicacy in some parts of the world, most of us are content with our unfertilized eggs for cooking and eating purposes. The problem is, unless you know what to look for, it can be difficult to tell the difference between the two types of eggs without cracking them open.

The Anatomy of an Egg

Before discussing how to tell the difference between fertilized and unfertilized eggs, it is important to understand the anatomy of an egg. Eggs are composed of several layers:

  • Shell: The outermost layer of the egg, which is porous and allows oxygen and carbon dioxide to pass through.
  • Shell membranes: Two thin, translucent layers beneath the shell that protect the egg from bacteria.
  • Albumen: Also known as the egg white, this is the clear, thick fluid that forms around the yolk of the egg.
  • Chalaza: Two twisted, rope-like strands present in the egg white that anchor the yolk in place.
  • Yolk: The yellow, nutrient-rich center of the egg.
  • Germinal disc: A small, white spot on the surface of the yolk that indicates whether or not the egg has been fertilized.

Now that we understand the basic anatomy of an egg, we can move on to discussing how to tell the difference between fertilized and unfertilized eggs.

The Process of Fertilization in Eggs

When it comes to differentiating fertilized and unfertilized eggs, understanding the process of fertilization is crucial. Fertilization occurs when the sperm from a male animal joins with the egg from a female animal. This union creates an embryo, eventually leading to the development of a new life.

  • The process of fertilization typically occurs inside the female animal’s body, such as in the ovaries or oviducts (also known as fallopian tubes).
  • During mating, the male animal deposits his sperm inside the female animal’s reproductive tract.
  • The sperm then swims through the female’s reproductive tract towards the egg.
  • The sperm penetrates the egg, and the nuclei of the sperm and egg fuse together, forming a zygote.

After fertilization, the zygote begins to divide and form into an embryo. It then travels towards the uterus for implantation and further development.

It’s important to note that not all eggs are fertilized. In fact, many domesticated chicken eggs sold in supermarkets are unfertilized because they are laid by hens without the presence of a rooster.

Signs of fertilized eggs Signs of unfertilized eggs
Visible blood vessels inside the egg when candled No visible blood vessels when candled
The yolk appears cloudy or slightly misshapen The yolk appears round and intact
The egg feels slightly heavier The egg feels lighter

If you are unsure whether an egg is fertilized or not, candling is an effective method for determining the presence of a developing embryo. Candling refers to shining a bright light through the egg to visualize the contents inside. With a fertilized egg, you should be able to see blood vessels and the developing embryo inside the egg.

Understanding the process of fertilization and the signs that indicate a fertilized egg can help you make a more informed decision when purchasing or consuming eggs.

Factors Affecting Egg Fertility

When it comes to distinguishing fertilized and unfertilized eggs, one of the most important factors to consider is egg fertility. In simple terms, egg fertility is the ability of an egg to develop into an embryo after being fertilized by a sperm. Here are some of the factors that affect egg fertility:

  • Age of the Hen: A hen’s age has a significant impact on the fertility of her eggs. The younger the hen, the more fertile her eggs are likely to be. After a hen reaches 5 or 6 years of age, her fertility decreases significantly.
  • Diet: The diet of a hen can also influence the fertility of her eggs. Hens that are fed a well-balanced diet that includes the right amount of protein, vitamins, and minerals are more likely to lay fertile eggs.
  • Breeding: The breeding of hens also plays a role in egg fertility. Hens that are bred with roosters that have good fertility rates are more likely to lay fertile eggs.

Factors Affecting Egg Quality

Aside from egg fertility, there are other factors that can influence the quality of eggs. Here are some of them:

  • Storage: The way you store your eggs can affect their quality. Eggs should be stored in a cool and dry place, at an ideal temperature of 45-50°F.
  • Hygiene: The cleanliness of the hen’s environment is crucial to the quality of her eggs. Hens that are kept in dirty environments or are exposed to bacteria are more likely to lay low-quality eggs.
  • Stress: Hens that are under stress or exposed to stressful situations are more likely to lay poor-quality eggs. Stress can be caused by overcrowding, poor nutrition, or illness.

Egg Fertility Chart

If you’re still having trouble distinguishing between fertilized and unfertilized eggs, you can refer to this egg fertility chart:

Type of Egg Appearance
Unfertilized White or pale yellow yolk
Fertilized Bullseye pattern on the yolk, which indicates the presence of a developing embryo

By considering all these factors, you can tell the difference between fertilized and unfertilized eggs with confidence.

Physical differences between fertilized and unfertilized eggs

In order to tell the difference between fertilized and unfertilized eggs, there are physical differences that can be observed. These include:

  • The appearance of the yolk: In a fertilized egg, the yolk will appear darker and slightly more defined than that of an unfertilized egg. This is because the fertilized egg contains an embryo that is developing.
  • The presence of a white spot: When viewing the yolk of a fertilized egg using a candling method (placing a bright light behind the egg), a small white spot may be visible. This is the developing embryo and is not present in an unfertilized egg.
  • The size of the egg: Fertilized eggs will usually be larger than unfertilized eggs, as they contain both the yolk and the developing embryo, which adds additional mass to the egg.

While these physical differences can be observed, it is important to note that they are not always completely reliable. For example, some unfertilized eggs may still have a slightly darker yolk or appear larger than usual due to natural variations within the laying hen’s reproductive system.

For more accurate determination of fertilization, it is recommended to use a reliable method such as candling or egg incubation, as these can provide more conclusive results.

Physical Differences Fertilized Egg Unfertilized Egg
Yolk Appearance Darker, more defined Lighter and less defined
Presence of white spot Visible Not visible
Size of egg Larger than an unfertilized egg Smaller than a fertilized egg

Overall, while physical differences can indicate whether an egg is fertilized or not, it is important to use reliable methods such as candling or egg incubation for more conclusive results.

The Importance of Identifying Fertilized Eggs in Farming

Knowing how to distinguish fertilized from unfertilized eggs is crucial in the farming industry. This is because fertilized eggs are the foundation of livestock reproduction, and it is essential for animal breeders to have a correct system for separating these eggs for various purposes.

  • Optimizing Production: By identifying the fertilized eggs, the farmer can isolate and appropriate them for incubation. On the other hand, unfertilized eggs are either sold for consumption or used as fertilizers for farming soil. Proper identification of fertilized eggs allows for optimized productivity and better planning in the farming process.
  • Preventing Inbreeding: Breeding animals with inbred genes can cause genetic disorders, leading to health issues and decreased fertility rates. Separating fertilized eggs ensures that there is no inbreeding among animals on the farm.
  • Ensuring Quality: Separating fertilized eggs from unfertilized eggs ensures that only quality products are sold or used. Fertilized eggs that may be underdeveloped, have cracks, or other issues, can be sorted out and discarded, while only good quality eggs will be used for incubation or sale.

Identifying Fertilized Eggs

There are several ways to identify fertilized eggs in farming:

  • Candling: Candling is the process of holding an egg to a bright light to see its internal contents. Fertilized eggs will have a visible embryo that may appear as a dark spot.
  • Incubation: Placing eggs in an incubator for a few days can help in categorizing fertilized eggs from unfertilized ones. Fertilized eggs will have developed embryos and will start showing signs of hatching.
  • Checking behavior: During the breeding season, the appearance of the rooster can signal the presence of fertilized eggs. If the rooster takes an interest in the eggs or is protecting them, the chances are high that some or all of them are fertilized.


Farmers must have a system in place to identify fertilized eggs in their livestock for maximum productivity and produce. By separating fertilized eggs from unfertilized ones, farmers can control inbreeding, ensure quality, and maximize profits.

Fertilized Eggs Unfertilized Eggs
Can be incubated for hatching Used as human food or fertilizer
Indicate continuation of animal breed Cannot reproduce
Require different handling process No further processing required

Knowing how to identify fertilized eggs is an essential part of efficient farming and livestock production. With proper identification, farmers can ensure that their livestock is healthy, breeding is regulated, and productivity is optimized.

Challenges in Detecting Fertilized Eggs Using Candling Method

The candling method is a commonly used method to detect whether an egg is fertilized or not. Candling involves using a bright light source to illuminate the egg, giving a clear view of the interior. However, even with this method, it can be challenging to determine whether the egg is fertilized or not due to the following reasons:

  • No outward physical signs: Unlike mammals, eggs do not have external genitalia or visible physical signs of fertilization. So, it is impossible to tell whether an egg is fertilized simply by looking at it from the outside.
  • Difficulty in observing early stage development: In the early stages of embryonic development, there is a negligible difference in appearance between fertilized and unfertilized eggs. It can be challenging to distinguish them apart until the embryos have developed beyond a certain point.
  • Inconsistent markers: Even if you are using a high-quality candling device, it can be tough to detect the subtle changes that happen in a fertilized egg. While some fertilized eggs may display an obvious, early development, others may not show any signs of fertilization until much later, if at all.

To overcome these challenges, it is essential to have a trained eye, patience, and an understanding of what to look for when candling eggs.

How to Tell if an Egg is Fertilized or Not

Although candling may seem like an easy task, it requires careful attention so as not to cause harm to the developing embryo. When candling, use a gentle light source, and follow these steps:

  • Choose a properly incubated egg: Ensure that your egg has been under the correct incubation temperature and humidity levels for at least a week before attempting to candle it.
  • Find the air cell: At the blunt end of the egg, identify the air cell, which is a small, empty compartment between the inner and outer membranes and the shell.
  • Candle in a dark room: At this point, move to a dark room and place a flashlight at the broad end of the egg. The beam should pass through the air cell and then through the yolk and egg white onto the inner membrane.
  • Observe the egg: Check for signs of growth, such as the formation of tiny blood vessels within the yolk or a cloudy white ring surrounding the air cell. If you observe these signs, it is likely that the egg is fertilized.
  • Keep a record: Keeping a record of the developmental changes you observe in your candled eggs can help you learn how to differentiate between fertilized and unfertilized eggs.

Candling During the First Few Days

The first few days of development are the most challenging to detect using the candling method. The embryo is still in the process of dividing, and there are no visible signs of fertilization at this stage. However, with experience, you may begin to see a slight shadow or outline of the developing embryo or a small accumulation of cells within the yolk.

Day of Incubation Visible Sign of Fertilization
1 to 3 No visible sign of fertilization
4 to 5 Formation of blood vessels*
6 to 8 Embryo development begins (visible movement)**
9 to 12 Embryo growth continues (visible heartbeat)**
13 to 18 Embryo features become more evident**
19 to 21 Chick begins to position itself for hatching*
21 Hatching begins*

*Visible changes in the egg that will confirm it is fertilized, but not a clear indicator of the embryo’s viability.

**Clear indication of the embryo’s viability.

The candling method is a tricky process, and it may take a while to develop the skills necessary to distinguish between fertilized and unfertilized eggs. However, once you master this skill, it can be an exciting experience to track the development of chicks from eggs.

Ethical considerations when dealing with fertilized eggs

When dealing with fertilized eggs, there are ethical considerations that need to be taken into account. These considerations are important because they involve the potential for life and the well-being of living beings. Here are some key ethical considerations to keep in mind:

  • Respect for life: Fertilized eggs have the potential to develop into living beings, so it’s important to respect the life that they represent. This means treating them with care and making decisions that prioritize their well-being.
  • Choice and autonomy: Individuals and couples who use in vitro fertilization (IVF) to conceive have the right to make choices about their reproductive health. This includes deciding what to do with fertilized eggs that are not used in the conception process. It’s important to respect their autonomy and choices regarding the use of these eggs.
  • Quality of life: When considering the use of fertilized eggs, it’s important to think about the quality of life that the resulting offspring could have. This means taking into account genetic factors and potential health issues that may arise. It’s important to make decisions that prioritize the well-being of any potential offspring.

These ethical considerations can be complex and require careful thought and consideration. It’s important to remember that the decisions made regarding fertilized eggs have real-life consequences and should not be taken lightly.

How do you tell the difference between fertilized and unfertilized eggs?

1. Can you eat fertilized eggs?

Yes, fertilized eggs are safe to eat. The only difference is that there might be a small white spot on the yolk, which is the embryo. However, if the egg is older than a week, the embryo will not develop and the egg will look exactly like an unfertilized egg.

2. What does a fertilized egg look like?

A fertilized egg will have a small white spot on the yolk, which is the embryo. The spot might be hard to see, especially in brown eggs. However, if you crack the egg open and look closely at the yolk, you will see the spot.

3. Can you hatch a fertilized egg?

Yes, you can hatch a fertilized egg if you have a broody hen or an incubator. However, not all fertilized eggs will hatch. You need to make sure that the egg is kept at the right temperature and humidity for the embryo to develop.

4. How long does it take for an egg to be fertilized?

It takes about 24 to 30 hours for an egg to be fertilized after it is laid. After that, it takes about 21 days for the embryo to fully develop and hatch. During this time, you can tell if the egg is fertilized by candling it, which means shining a light through the egg to see the embryo.

5. How do you prevent eggs from being fertilized?

If you have hens, you can prevent eggs from being fertilized by keeping the rooster away from them. If you buy eggs from the store, they are already unfertilized because they were not exposed to a rooster.

Closing Words

Thank you for reading our article on how to tell the difference between fertilized and unfertilized eggs. We hope this has been helpful to you. If you have any further questions or comments, please feel free to reach out to us. Don’t forget to come back later for more useful tips and information!