Egg Incubation Guide Part 3 Monitoring and Candling During Incubation

Introduction
Egg incubation is not just about setting the right temperature and waiting—it’s a process of precision, care, and daily attention. From monitoring temperature and humidity to turning eggs and candling for embryo development, every step matters. In this guide, we’ll walk you through daily checks, key candling stages, and how to prepare for successful hatching.
Daily Monitoring and Record Keeping
Stable environmental conditions are essential for embryo health. For chicken eggs, maintain a temperature between 37.5°C–37.8°C (99.5°F–100°F) in forced air incubators, or 38.6°C (101.5°F) measured at egg top level in still air incubators.
Humidity should be managed in phases:
- Days 1-17: 45-55% relative humidity
- Days 18-21 (lockdown): 65-75% relative humidity
It's recommended to check both temperature and humidity 2 to 4 times daily—in the morning, afternoon, evening, and before bedtime. Temperature fluctuations of more than 1°C (2°F) can significantly affect hatch rates.
When refilling water, use warm water to avoid chilling the eggs. The water tray's surface area also affects humidity levels, so adjust it as incubation progresses.
If you're using an automatic egg turner, check daily that it's functioning correctly. For manual turning, rotate the eggs gently 4 to 6 times a day, at an angle between 90° and 180°. Remember to stop all turning during the last 3 days of incubation (lockdown period).
Proper ventilation is also critical. Keep the incubator's vent holes open as instructed in the user manual, and increase airflow slightly in the later stages to meet the embryo's growing oxygen needs. Place your incubator in a well-ventilated room, away from direct drafts or temperature fluctuations.
�� To ensure consistency, maintain a daily log that includes temperature and humidity readings, turning activity, water refills, and any unusual events like power outages or device malfunctions.
�� New to incubation? Start with our Pre-Incubation Preparation Guide.
Candling: Checking Embryo Development
Candling helps you assess whether your eggs are fertile and progressing properly. Using a bright light or egg candler, you can view the embryo's development through the shell in a dark room. Candling also allows you to identify infertile or dead eggs that should be removed to avoid contamination.
��What You Need:A strong flashlight or egg candler and a dark room setup.
⚠️Safety Note: Always handle eggs gently and candle quickly to avoid heat loss or shock. Keep candling sessions brief (30 seconds per egg maximum) and work in a warm room.
Here are the three recommended candling stages for chicken eggs:
Day 5–7 (First Candling):Fertile eggs show web-like blood vessels spreading from a central point and a visible dark eye spot. Infertile eggs remain clear. Dead embryos may show blood rings (thin red circles) or blood streaks without organized development.
Day 10–13 (Second Candling, Optional):Most of the egg appears dark due to embryo growth. The air cell is clearly defined, and you may see slight movement inside. Blood vessels may be less visible due to the embryo's size filling more of the egg.
Day 17 (Final Candling Before Lockdown):The egg looks almost entirely dark, with only the air cell visible at the blunt end. A sloped or wavy edge of the air cell usually signals active development and proper chick positioning. After this stage, stop turning and move the eggs to the hatching tray.
✏️ Use a pencil to mark and remove any infertile or dead eggs at each candling stage.
Success rates:Expect 70-85% fertility in eggs from healthy breeding flocks. Remove any eggs showing no development, irregular blood patterns, or foul odors.
Adjusting Humidity Before Hatching
The final 3 days of incubation (lockdown) require a different environment. During this time, increasing humidity helps prevent the inner membrane from drying out and trapping the chick inside the shell.
�� Target Humidity Range: Raise the relative humidity to 65–75%.
To boost humidity, add moist, sterilized sponges or cloths to increase surface area inside the incubator. Ensure these materials do not touch the eggs. Always use warm water when refilling to avoid sudden temperature drops.
�� Avoid spraying water directly onto the eggs. Over-humidifying can cause oxygen reduction or mold growth, so keep ventilation balanced even in lockdown.
�� Need more help with environmental settings? Visit our full Incubation Guide Series.
�� Conclusion: Consistency Leads to Success
Embryos may develop silently, but they require precise conditions every day. By following consistent monitoring practices, candling at the right times, and adjusting humidity during the lockdown phase, you significantly increase the chances of a successful hatch.
�� Looking for an incubator with built-in controls? See our chicken egg incubator selection or browse the full poultry incubator collection including models for ducks, geese, turkeys, and quail.
�� Ready for the big day? Continue reading Part 4: Hatch Day and Late-Stage Management to learn how to support your chicks as they emerge.