Incubation Humidity For a Successful Hatch

Controlling incubation humidity for a successful hatch ensures that moisture evaporates from poultry eggs at just the right rate. Humidity is a measure of the amount of moisture in the air. At a given temperature, the drier the air, the more rapidly the air absorbs moisture. The more moisture the air already holds, the less additional moisture it can absorb.

Applying this concept to incubation, the drier the air in the incubator, the more rapidly moisture will evaporate from the eggs through their shells. The moister the incubator’s air, the more slowly moisture will evaporate from the eggs. Incorrect humidity can cause embryos to die in the shell or result in abnormal chicks.

Humidity Too Low

When humidity is too low, embryos in the early stage of incubation may adhere to the shell membrane and die. Those that continue to grow may remain small and too weak to pip. They may pip and not hatch, or may crack the shell all the way around but be unable to free themselves from a dried-out membrane. If a chick manages to struggle free, or you help it out, it may have a twisted neck or crooked feet, or be unable to stand.

Low humidity tends to be a problem with a small incubator that has an inadequate water container. It also occurs in a large incubator that is not filled to capacity. And it can happen in any incubator that must be frequently opened to turn the eggs manually.

A sudden drop in humidity during a hatch may mean the water pan is coated with chick fluff. All that fluff prevents evaporation, causing humidity to plummet.

Humidity Too High

When incubation humidity is too high, embryos grow too large inside the shell to move into hatching position. If they do manage to break into the air cell, it won’t provide sufficient oxygen, and the term embryo may suffocate or be too weak to break out of the shell. Those that do hatch will be large, soft, and sluggish.

Excessive incubation humidity is usually caused by inadequate ventilation or high ambient humidity. An accumulation of moisture on the incubator’s observation window during the hatch is an obvious sign of excess humidity.

Proper Humidity

The necessary humidity for a successful hatch is not steady from start to finish, but is higher during the hatch than during the rest of incubation. In nature the first chicks to hatch contribute to humidity under the hen, thus assisting the later, and typically weaker, chicks to get free of their shells.

Adequate humidity during the hatch prevents the shell membranes from drying out and sticking to the emerging embryos, a condition that effectively puts them into a straitjacket and prevents them from getting out of the shell. Some of the factors affecting humidity adjustment include these:

• Egg size — smaller eggs, like bantam and guinea, need more humidity
• Egg type — waterfowl eggs need more humidity than land fowl eggs
• Shell porosity — porous shells, produced as summer progresses, require higher humidity
• Shell thickness — thin shells produced by aging hens require higher humidity
• Number of eggs — an incubator not filled to capacity needs higher humidity
• Elevation — high altitudes are drier, requiring higher incubation humidity

Monitoring Humidity

The time-honored way to monitor humidity is to candle the eggs to examine the changing air-cell size. Eggs that take 21 days to hatch are typically candled on days 7, 14, and 18. Eggs that take 28 days or longer to hatch are candled on days 7, 14, 21, and 26. If air cells are proportionately larger than those shown in the sketch, increase humidity; if they’re smaller, decrease humidity.

A chick breaks into the air cell before it breaks out of the shell, so examining the shape of the shell after hatch can give you an important clue about the humidity level. A chick should occupy approximately two-thirds of the shell, with the air cell taking up the remaining third. Humidity is correct when the bottom part of the shell is approximately twice as large as the cap. If the cap is much smaller than half, humidity is too high; if it’s much larger than half, humidity is too low.

Adjusting Humidity

Here in Tennessee, our weather conditions can change from one day to the next — cool and dry one day, hot and humid the next. Adjusting incubation humidity can be tricky in a room that is not climate controlled.

My counter-top incubators are small enough to keep in the air-conditioned house. The larger cabinet-size models take up too much space to keep in the house. They are operated in a clean room at the barn, making humidity control more difficult.

The best way to adjust humidity is to let the incubator do it for you. With an R-Com incubator, for instance, you simply set the required humidity level and the computerized incubator handles the rest.

An incubator with a digital readout, such as those made by GQF, shows the current humidity level. But it’s up to you to make any necessary adjustments.

Each incubator is a little bit different, as is each incubation situation insofar as type and number of eggs hatched and conditions where the incubator is located. By using the details in your incubator’s operating manual as a starting point, then fine-tuning as you gain experience, you can learn to adjust incubation humidity just right for a successful hatch.