Hatchability — the proportion of fertile eggs that produce a healthy, saleable day-old chick — is the hatchery's single scorecard metric. A commercial chicken hatchery should expect 85–90% on fertile eggs set, with top-tier operations reaching 92–95%. Values below 80% almost always indicate a specific, identifiable problem, not generic bad luck.

This article walks through the full incubation pipeline — egg handling, storage, setting, candling, hatching, chick processing — and the handful of variables that most reliably decide the outcome.

Before incubation — egg handling makes or breaks hatchability

Hatchability is already partly decided before the egg reaches the incubator. The decisions made on the breeder farm and during transport account for roughly 30% of hatchability variation.

Collect often

In temperate climates, collect eggs at least four times per day; in hot climates, six times. Every hour an egg spends in the nest is an hour of bacterial contamination, cooling and physical risk from other hens.

Select strictly

Only set eggs that are:

• Clean (reject anything with visible dirt or faecal matter — do not wash hatching eggs; washing drives bacteria through the shell).
• Normal in shape (reject misshapen, pointed-both-ends, excessively round).
• Within weight range for the breed (reject outliers — typically ±5g from breed standard).
• Free of cracks (candle every egg before setting, no exceptions).
• From hens of appropriate age (reject eggs from pullets younger than 24 weeks or hens older than 60 weeks for best hatchability).

Store properly

Hatching eggs are living organisms in suspended animation. Treat them accordingly:

• Store at 15–18°C and 75% relative humidity.
• Store pointed end down.
• Rotate trays once per day during storage (prevents yolk sticking to shell membrane).
• Set within 7 days of lay for best results; hatchability drops approximately 1% per day of storage beyond Day 7.

Setting day — the first 24 hours matter

Move eggs from cool storage to the incubator slowly. Sudden temperature change causes condensation on the shell ("sweating"), which drives microbes inside. Pre-warm eggs for 6 hours at 25°C before setting.

Load the incubator at a consistent time each setting day. This matters because the hatcher pull is counted exactly 21 days later; variable set times mean variable hatch windows and compromised chick quality.

Days 1–18 — the setter phase

Four parameters matter: temperature, humidity, turning and ventilation.

Temperature

Target 37.8°C (100°F) ± 0.1°C for a single-stage machine, or a programmed profile for multi-stage. Chicken embryos tolerate a very narrow range — a sustained excursion of 0.5°C will reduce hatchability by 5–10%.

Measure with a calibrated digital thermometer in two places inside the machine. Trust the readings, not the display, until you've verified they agree. Many hatcheries lose 2–3 points of hatchability every month to a lazy thermistor.

Humidity

Target 50–55% relative humidity during the setter phase. Humidity controls weight loss of the egg — chicken eggs should lose 11–13% of their initial weight by Day 18, through evaporation across the shell. Too little weight loss (low ventilation or high humidity): the chick drowns in retained fluid. Too much (low humidity): the chick sticks to the membrane and cannot pip.

Weigh a tray of eggs on Day 0, Day 7, Day 14, Day 18. Adjust humidity based on the weight-loss trajectory, not on gut feeling.

Turning

Chicken eggs must be turned at least every hour during Days 1–18. Modern setters turn automatically every 60 minutes through a 45° arc. Turning prevents the embryo from adhering to the shell membrane and ensures nutrient distribution in the yolk.

Stop turning on Day 18. By that point the chick is positioned for hatching, and continued turning disorients it.

Ventilation

Embryos need oxygen. CO₂ must stay below 0.5% and preferably below 0.3% in a properly ventilated setter. In high-altitude installations the oxygen target rises accordingly. If your incubator is airtight (older farm-type machines often are), you can lose 15% of hatchability to accumulated CO₂ alone.

Candling schedule

Candling means shining a strong light through the egg to see inside. Done well, it is a diagnostic X-ray; done poorly, it is a waste of time and a thermal shock to the embryo.

Day 7 candling

Look for a developing embryo with visible blood vessels. Remove clear eggs (infertile) and blood rings (early death). Expected clear + blood ring rate: 5–10% of fertile eggs set.

Day 14 candling (optional)

Confirm continued development. Remove any eggs with no visible dark mass (mid-term death). Expected mid-term mortality: 1–3%.

Day 18 transfer candling

Move live eggs from the setter to the hatcher. Any egg still visibly clear or showing mid-term death is removed. This is also the moment to stop turning and begin the hatcher humidity ramp.

Days 18–21 — the hatcher phase

The hatcher is a separate chamber (or program) with different environmental settings. The chick is now completing its final preparations: positioning in the shell, drawing the yolk sac into the body cavity, breaking the inner membrane and finally pipping the shell.

Hatcher settings

• Temperature: 36.8–37.2°C (slightly below the setter — the embryos now produce their own heat).
• Humidity: ramp from 55% at transfer to 65–70% at pipping, up to 75% at mass hatch.
• Ventilation: increase significantly — CO₂ should stay below 0.5%.
• No turning.

Do not open the hatcher between transfer and pull. Every opening drops humidity, every drop in humidity means stuck chicks.

Day 21 — the pull

Pull chicks when the hatch window is 95% complete and most chicks are dry and fluffy. Pulling too early produces wet, weak chicks; pulling too late results in dehydration, excessive navel inflammation and reduced first-week livability.

The ideal hatch window is tight — 24 to 36 hours between the first chick hatching and the last. A hatch window longer than 48 hours indicates an uneven incubation profile (temperature variation across the setter or variable egg quality).

Chick quality — what to grade

Not every chick that hatches is saleable. Grade on these criteria at pull:

• Fluffy and dry (not sticky, not wet).
• Alert and active (not listless).
• Navel area closed, dry, no scab.
• Yolk sac fully absorbed.
• Legs straight, no curled toes.
• Eyes bright and clear.
• Beak straight, no cross-beak.
• Weight within breed standard (typically 36–42g for layers at hatch).

Grade A chicks ship or sell. Grade B chicks (minor issues such as slightly delayed navel closure) go to the farm's own replacement stock or to local buyers at a discount. Grade C and dead-in-shell are discarded.

Diagnosing a bad hatch

When hatchability falls below expected, the dead-in-shell pattern tells the story:

• Day 1–7 dead → old eggs, improper storage, rough handling, infection.
• Day 8–14 dead → genetics, nutrition of the breeder flock, mycotoxins in feed.
• Day 15–18 dead → low humidity, poor ventilation, position in machine.
• Pipped but not hatched (dead with beak through membrane) → humidity too low or too high at hatch, pipped shell too hard.
• Hatched but dead within 24h → excessive humidity at hatch, drowning, dehydration from delayed pull.

A monthly post-mortem of 50 unhatched eggs will tell you exactly where in the pipeline your losses are coming from.

Hygiene

Hatcheries are warm, humid, protein-rich environments. If they are not relentlessly cleaned, they become bacterial amplifiers. The non-negotiables:

• Fumigate hatchers between every batch (formalin + potassium permanganate, or equivalent).
• Wash and disinfect setter trays, hatcher baskets and chick boxes after every use.
• Clean the hatcher ductwork quarterly.
• Separate dirty and clean areas with hard physical barriers — the "fluff room" is where dust and down accumulate; it must never share airflow with the setter.
• Change shoes between zones. Shoes carry everything.

Record keeping for hatcheries

Every setting is a batch. Every batch gets:

• Egg source (farm, house, breeder flock age)
• Collection dates and conditions
• Storage duration and conditions
• Set date and operator
• Machine ID and position
• Humidity + temperature logs
• Candling results at each phase
• Transfer date and operator
• Pull date, Grade A count, Grade B count, culls, pipped-not-hatched

Analyse by source farm quarterly. The farm with chronically lower hatchability has a management or genetics issue — resolve it collaboratively, not punitively.

"A hatchery is not a magic black box. It is 10,000 small decisions, every one of which can be measured."

Closing thought

Hatchery work is unforgiving — every number is an outcome of a hundred prior decisions. The reward is also exceptional: when it works, you deliver thousands of lives into the world, every single week, and set the next cycle of poultry production in motion. Few agricultural activities are more satisfying.