Incubation and Hatching: Critical Requirements for Setter and Hatcher Phases

A fertilized chicken egg carries everything it needs to develop into a healthy chick – but only if the conditions around it are precisely right. From the moment an egg enters an incubator, temperature, humidity, ventilation, and positioning work together to support one of the most complex biological processes in poultry production. Getting these conditions right across both phases of incubation – the setter and the hatcher – is the single most important factor in maximizing hatch rates and producing strong, viable chicks.

The two-phase incubation system 🔗

Commercial incubation of chicken eggs is split into two distinct phases managed in two separate machines: the setter and the hatcher. The total incubation period for chickens is 21 days. The setter handles the first 18 days, when the embryo develops from a cluster of cells into a fully formed chick. The hatcher takes over for the final three days, during which the chick completes its development, positions itself, and breaks out of the shell.

Each phase has its own environmental requirements. According to Tamil Nadu Agricultural University’s poultry expert system, the five core factors governing successful incubation are temperature, humidity, ventilation, egg position, and egg turning – all of which shift in importance or specification between the two phases.

The setter phase: days 1 to 18 🔗

The setter is where embryonic development takes place. During these 18 days, every major organ system forms – the heart begins beating around day 3, blood vessels spread across the yolk by day 6, and by day 18 the embryo has grown to fill most of the egg. Maintaining stable environmental conditions throughout this period is critical, as developing embryos can only tolerate very small fluctuations.

Temperature in the setter 🔗

Temperature is the most critical variable in incubation. Tamil Nadu Agricultural University notes that embryonic development only begins once temperature exceeds the “physiological zero” – around 24°C (75°F) for chicken eggs. Below this threshold, growth stops entirely.

The recommended setter temperature for chicken eggs ranges from 37.6°C to 37.9°C (99.5°F to 99.75°F). Hatching Time’s complete incubation guide confirms that temperatures above 38.3°C can harm embryos, and even brief exposure to temperatures above 39.4°C (103°F) can be fatal. Cooler temperatures slow development and delay hatching. The window is narrow, which is why reliable thermometers – ideally two independent ones – are essential in any setter.

Humidity in the setter 🔗

Humidity in the setter controls the rate of moisture evaporation from the egg. Backyard Poultry explains that eggshells are porous, and moisture naturally moves from the egg’s interior to the drier surrounding air. If humidity is too low, eggs lose excessive moisture and the resulting chicks are smaller and weaker. If humidity is too high, insufficient moisture evaporates, leaving too little air space inside the egg for the chick to breathe during hatching.

The standard recommendation for the setter phase is 55% relative humidity, though some sources cite a range of 55-60%. Farmer Boy’s hatchery guide suggests using a hygrometer to track this daily, and notes that humidity can be adjusted by modifying the size of water reservoirs or the level of ventilation inside the machine.

Egg positioning 🔗

How eggs are positioned in the setter matters more than many people realize. TNAU’s incubation resource explains that eggs should be placed with the broad end (air cell end) facing up. This allows the chick’s head to naturally orient toward the air cell, which is where it will pip (break through) to initiate breathing before hatching. When eggs are placed small-end up, research shows that roughly 60% of embryos will develop with the head near the wrong end – meaning the chick cannot reach the air cell when it needs to breathe, resulting in late-stage mortality.

Purina Animal Nutrition’s 21-day guide also recommends this broad-end-up orientation in setter trays, and confirms it is standard practice in both commercial and small-scale operations.

Egg turning in the setter 🔗

Regular turning is one of the most biologically significant actions in the setter phase. Without it, embryo mortality rises sharply – especially in the first week of incubation. The Poultry Site’s research review on egg turning explains that turning is not primarily about preventing yolk adhesion, as once thought – it is essential for the correct formation of extra-embryonic membranes, including the amnion and chorioallantoic membrane, which deliver oxygen and nutrients to the developing embryo.

Purina highlights the mechanical reason too: the yolk tends to float upward within the egg white. If the egg is not turned, the embryo can become pressed between the buoyant yolk and the shell, causing fatal damage. Turning rotates the yolk within the albumen, keeping the embryo safely positioned.

Poultry Performance Plus reports that in commercial setters, eggs are typically turned once every hour, with a minimum of once every four hours (six times per day). Turning less frequently than this impairs hatchability. A peer-reviewed study published in PubMed Central found that eggs turned 24 times per day achieved the highest hatchability rates, while reducing to 3 turns per day caused a nearly 20% drop in hatch of fertile eggs. Turning must continue through day 18, after which it stops when eggs are transferred to the hatcher.

The optimal turning angle is 45 degrees on either side of the egg’s long axis, and the direction should alternate – turning always in the same direction can wind up the chalaza (the membrane anchoring the yolk) and cause it to rupture.

The hatcher phase: days 18 to 21 🔗

On day 18, eggs are transferred from the setter to the hatcher. At this point, the chick is fully formed and begins the process of orienting itself for hatching. The hatcher provides a different set of environmental conditions tailored to support the chick’s transition from inside the egg to the outside world.

Temperature in the hatcher 🔗

The hatcher operates at a slightly lower temperature than the setter: typically 36.1°C to 36.7°C (97°F to 98°F), though some sources cite 98.5°F (36.9°C) as the standard. TNAU lists the hatcher optimum at 98.5°F. The reason for this reduction is that hatching chicks themselves generate metabolic heat as they exert energy breaking through the shell, so the machine temperature is reduced to prevent overheating.

Research by Petersime, a leading incubation equipment manufacturer, has confirmed that even small deviations from the optimal eggshell temperature during the hatcher phase – as little as ±0.8°C – can measurably affect both hatchability and chick quality. Early hatches tend to signal that the temperature is running too high; late hatches point to temperatures being too low.

Humidity in the hatcher 🔗

Humidity increases significantly in the hatcher. The recommended level rises to 65%, with some sources recommending up to 70-75%. TNAU recommends a range of 65-75% for the hatching period, noting that higher humidity prevents chick dehydration. This is especially important because as chicks pip and begin breathing, their respiratory membranes must remain moist. Backyard Poultry explains that if these membranes dry out and adhere to the chick’s body, the chick can become physically stuck inside the shell and unable to complete hatching.

Monitoring humidity becomes more complex in the hatcher because newly hatched chicks, broken shell fragments, and fluff can create localized variations within the chamber. Good ventilation design helps maintain even humidity distribution throughout.

No turning in the hatcher 🔗

Once eggs are moved to the hatcher, turning stops entirely. By day 18, the chick has completed its developmental positioning and needs to remain undisturbed to orient its head toward the air cell and begin the pipping process. Purina confirms that eggs should be placed horizontally (on their sides) in hatcher baskets at this stage, allowing the chick to rotate freely within the egg as it “zips” around the shell before pushing out.

Ventilation in the hatcher 🔗

Ventilation requirements increase during the hatcher phase because newly pipping chicks begin breathing air directly for the first time. TNAU’s expert system notes that carbon dioxide levels in the incubator should not exceed 0.4%, and that fresh air circulation must be sufficient to supply oxygen to hatching chicks without creating cold drafts. The hatcher room itself is kept sealed from the setter room during hatching to prevent cross-contamination from chick fluff and debris.

What happens when conditions are wrong 🔗

The relationship between environmental conditions and hatch outcomes is well established. Hatching Time’s guide summarizes the most common failure patterns: early hatches suggest the temperature has been running too high; late or slow hatches indicate temperatures were too low. Sticky or difficult hatches – where chicks struggle to leave the shell – typically point to humidity problems, either too low during the setter phase (causing membranes to dry out) or too low in the hatcher. Malpositioned embryos, where the chick’s head is at the wrong end of the egg at hatch time, are often linked to insufficient egg turning during the first week of incubation.

Under optimal conditions across both phases, commercial hatcheries can consistently achieve hatch rates of 85-90% or higher from fertile eggs. Even small, consistent deviations from recommended parameters – a degree too warm, humidity a few percentage points off – can bring those figures down significantly over time.

Summary of setter and hatcher requirements 🔗

To keep the critical specifications in one place: the setter maintains 37.6-37.9°C with 55% relative humidity, eggs broad-end up, and turning every 1-4 hours from day 1 through day 18. The hatcher operates at 36.1-36.7°C with 65-75% relative humidity, eggs laid horizontally, and no turning. Both phases require adequate fresh air ventilation, with CO₂ kept below 0.4%. These aren’t arbitrary numbers – they reflect the precise biological requirements of a developing embryo at each stage of its 21-day journey.

Consistent record-keeping, calibrated thermometers and hygrometers, and reliable turning mechanisms are not optional extras in a hatchery – they are the foundation of predictable, high-quality hatch outcomes.

What do you think? If a hatchery operator notices that chicks are consistently hatching one to two days late, which environmental parameter would you investigate first – and how would you go about diagnosing whether the issue lies in the setter phase, the hatcher phase, or both? And given how critical the first week of incubation is for embryo membrane development, how much do you think the frequency of egg turning is underappreciated compared to temperature and humidity in standard hatchery management?

References

1. https://agritech.tnau.ac.in/expert_system/poultry/Incubation%20and%20Hatching.html
2. https://hatchingtime.com/blogs/home/temperature-for-hatching-chicken-eggs
3. https://backyardpoultry.iamcountryside.com/eggs-meat/incubator-temperature-humidity-chicken-eggs/
4. https://farmerboyag.com/blog/maintaining-ideal-temperature-humidity-in-chicken-hatcheries/
5. https://www.purinamills.com/chicken-feed/education/detail/hatching-eggs-at-home-a-21-day-guide-for-baby-chicks
6. https://www.thepoultrysite.com/articles/the-biology-behind-egg-turning
7. https://poultryperformanceplus.com/information-database/incubation/170-turning-during-incubation
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC7598115/
9. https://www.petersime.com/expertise/the-effect-of-hot-and-cold-hatcher-temperature-profiles-on-hatchability-and-chick-quality