If you plan to incubate your eggs, it’s essential to determine whether the eggs are fertilized or not. Many novice chicken keepers have learned that placing unfertilized eggs in an incubator leads to an unpleasant, stinky mess. Unfertilized or “bad eggs” create a gas buildup, leading to messy egg explosions. When this happens, not only do you need to clean up the mess, but you also put your healthy eggs at risk of contamination.

Contaminated eggs prevent embryo growth, turn bad and explode, potentially creating an unfortunate chain effect in your incubator. However, many poultry keepers have learned to avoid this scenario by “candling” eggs to determine whether an egg is fertilized or unfertilized. QC Supply provides handy candling tips to spot fertile eggs and how to keep track of embryo progress to avoid incubation disasters.

What is Candling?

The term candling comes from the old-school method of literally holding a candle up to the eggs to reveal the yolk inside. Today, bright lights are used to check to see if the yolk has developed veins, the tell-tale sign of embryo development.

Fertilized vs. Unfertilized Eggs

An unfertilized egg will show the yolk or be completely clear, while a fertilized egg will show veining on the yolk or further details depending on the level of embryo development.

How to Use Candling to Determine Egg Fertilization Follow these steps to determine whether eggs are fertile or infertile:

• Store New Eggs For a Week Eggs must be stored for a week at a temperature between 53° F-59° F before candling. During this week, you should turn the eggs once a day, 45° each turn. Without daily turning, the yolk can float, touch the membranes, and get stuck, so the embryo can’t grow.
• Initial Candling A week after the egg is laid, you can do the initial candling to see if the egg is fertile. Although some embryos can be visible by day 4, day 7 is the safest bet to get a good look at the embryo.
• How to Candle the Egg Candling should be done in a completely dark room using a very bright light, such as the Cool-Lite Tester. Place the light on the larger end of the egg and rotate it until you have the best view of the egg’s insides.
• Fertilized vs. Unfertilized Eggs Embryos have dark lines running through the yolk, which are the embryo’s blood vessels. In the center of the yolk, you should also see a dark shape or shadow, which is the embryo. The blood vessels support the embryo and indicate you have a fertile egg with normal embryo development. If the yolk appears solid or the egg looks clear, it is infertile and can be thrown away.
• Second Candling On day 14, you can check the eggs again to make sure the embryo is developing properly. At this stage, you can often make out the beginnings of the chick’s eyes, beak, and toes. If the embryo has died, the egg will form a blood ring as the veins move away from the embryo.

Tips When Checking Fertilized Egg vs. Unfertilized Egg

Use these tips to help increase the chances of embryo survival:

• Only do 2 Candlings: Removing the egg from incubation for a 3rd candling can reduce the chances of the embryo surviving. Unless you suspect the embryo has died, avoid candling after day 14.
• Be Careful: This goes without saying, but be very careful when handling the eggs as you can easily rupture the yolk.
• Morning Collection: If you are candling your own eggs, collect them in the morning. This protects the egg from dirt & prevents predators (including hens) from eating the egg.
• Toss Misshapen Eggs: Misshapen eggs are less likely to hatch & tend to have faulty shells.
• Choose Medium-Sized Eggs: Smaller eggs don’t have enough space as the yolks are disproportionate to the albumen and shell, while larger eggs often have twins, so neither embryo survives.
• Temperature: When you store the eggs prior to incubation, the recommended temperature is noticeably lower than the incubation temperature of 99.5°F. Instead of placing fertile eggs directly into incubation, bring them slowly to room temperature first.

Candling is an age-old method to determine whether eggs are fertilized or not. These steps and tips will help increase the odds of your eggs hatching and producing healthy chicks.
Interested in finding the best products for your eggs? See our selection of poultry products available from QC Supply.

If you need further assistance, give our staff a call at 888-433-5275. We offer a full line of Egg Incubators & Equipment, and other poultry equipment you may need after your eggs are hatched!

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