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Incubation and egg candling

Article describing incubation and egg handling.

Whilst the majority of backyard flocks are bought in as point of lay pullets sourced from specialist breeders, markets and charitable organisations; a relatively small number of breeders hatch chicks annually for the domestic market.

As this is unregulated the exact numbers are difficult to estimate. In a backyard environment, natural incubation and maternal care is still the standard.

Natural Incubation:

  • The wild ancestors of chickens laid 8-12 eggs in a large clutch before starting the incubation process.
  • In contrast, domesticated chickens can easily incubate 12-16 eggs.
  • After producing 10-12 eggs, domesticated hens become strongly attached to a particular nesting box.
  • Hens readily share nest space with other laying hens during the process.
  • Some breeders use foster parents such as turkeys or ducks to incubate and hatch valuable eggs of highly prized strains with poor maternal instincts.
  • Live female incubation has a higher success rate (90%) than artificial incubators with automated egg rotators (80-90%) or hand rotation (50%).
  • A broody hen will pluck out breast feathering to produce a bald broody spot which is placed in close contact to the eggs and helps to transfer heat.
  • The hen remains on the nest covering the eggs with her own plumage, providing a warm humid environment and protecting the eggs from predators.

Artificial incubation:

  • An artificial incubator is more efficient than natural incubation during the winter months when domestic hens are less inclined to become broody.
  • More eggs can be hatched at one time.
  • For the first 15 days the environment is kept less humid at 45%.
  • Infertile eggs can be identified and removed at 10-12 days through the process of candling.
  • Water should be added to an incubator at 15-17 days and topped up regularly until 20 days have elapsed.
  • Once hatched the chicks should remain in the incubator until properly dried out and fluffed up.

Photo of chicks in a rearing cage with heat lamps Chicks in rearing cage, ©Brinsea Products Ltd

With industrial scale breeding worldwide having to meet the demand for both chicken meat and eggs, most birds alive today will have been hatched in a commercial incubator.

Commercial breeders run parent stock together; resultant eggs are collected three times weekly and stored in a hatchery for one week. The eggs are then transferred to an incubator, often referred to as a ‘setter unit’ in the commercial sector, where they remain for two weeks under strict temperature and humidity control.

The eggs are turned to mimic the movement of a parent bird, and at the end of two weeks the eggs are moved to a ‘hatcher unit’. At 21 days, when finally hatched, the chicks are sexed.

Chicks remain in a rearing unit up to the age of 16 weeks before being sent to laying units.

Information source: Steve Marriott, Hy-line

Hybrids are genetically modified on an ongoing basis to maximise meat and egg yield whilst maintaining or reducing costs and management resources.


The process of candling identifies eggs where no embryo is developing, and their removal allows for more efficient use of incubator space and minimises risk of infection.

The candling procedure involves projecting a light on the outside of the egg shining a light through the shell to show signs of growth inside the egg.

Photo showing the process of candling eggs to check embryo development Candling, ©The Incubator Shop

Photos showing candling photos during incubation to the point of hatch Embryo development as seen by candling, ©The Incubator Shop

Diagrams of chicken embryo development to the point of hatch Chicken embryo development ©The Incubator Shop

© University of Nottingham and the British Hen Welfare Trust
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Poultry Health

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