Not all chicken eggs will hatch, as the journey from a laid egg to a live chick is complex and depends on biological processes and environmental conditions. Even with optimal care, a certain percentage of eggs may not develop or hatch successfully. Understanding these reasons can shed light on avian reproduction and incubation practices.
The Role of Fertilization
For a chicken egg to hatch, it must be fertilized by a rooster. Hens lay eggs regularly regardless of a rooster’s presence; these “table eggs” are unfertilized and cannot develop into a chick. Fertilization occurs internally within the hen’s reproductive tract, shortly after the yolk is released and before the albumen and shell are formed. Roosters transfer sperm during mating, and hens can store sperm for up to several weeks, allowing subsequent eggs to be fertilized.
An unfertilized egg’s yolk has a small, dense white spot called a blastodisc. In contrast, a fertilized egg, even before incubation, displays a bullseye-like pattern on the yolk, known as a blastoderm, indicating cell division has begun. Without genetic material from both parents, an egg lacks the fundamental components for embryonic development, rendering it incapable of hatching.
Essential Incubation Conditions
Once an egg is fertilized, external environmental factors become paramount for successful embryonic development. The temperature during incubation is particularly important, with an optimal range for chicken eggs typically between 37.2°C and 37.8°C (99°F to 100°F). Deviations outside this narrow range, whether too high or too low, can hinder metabolic activities, cause deformities, or result in embryonic death, significantly reducing hatch rates.
Humidity levels inside the incubator are another critical factor, influencing the egg’s moisture loss. For chicken eggs, a relative humidity of 45-55% is generally recommended for most of the incubation period. This humidity helps ensure the egg loses the correct amount of water, allowing the air sac to form and enlarge. During the final three days before hatching, increasing the humidity to 55-75% can help soften the shell membranes, making it easier for the chick to emerge.
Regular turning of the eggs is also necessary to mimic a broody hen’s natural behavior and prevent the developing embryo from sticking to the shell membrane. Turning ensures even distribution of heat and nutrients, supporting the proper growth of extra-embryonic membranes. Eggs should typically be turned a minimum of three to five times daily, especially during the first week. This turning is usually discontinued around day 18, allowing the chick to orient itself for hatching.
Factors Affecting Embryonic Development
Even with proper incubation conditions, internal issues within the egg or embryo can prevent hatching. Genetic viability plays a role, as some embryos may carry lethal genetic defects that cause them to cease development. The nutritional status of the laying hen directly impacts egg quality; deficiencies in the hen’s diet can result in eggs lacking sufficient nutrients for healthy embryonic development. Embryonic diseases or infections can also lead to early death, sometimes indicated by bacterial growth. Physical damage to the egg, such as hairline cracks, can be detrimental. Even minor cracks can compromise the egg’s protective barriers, leading to excessive moisture loss and allowing harmful bacteria to enter, often resulting in embryonic mortality.
Identifying Eggs Unlikely to Hatch
To identify eggs unlikely to hatch, candling is commonly used, which involves shining a bright light through the eggshell in a darkened room. This allows for observation of the internal contents without breaking the shell. Candling is often performed around day 7 of incubation, where a fertile and developing egg typically shows a small dark spot (the embryo) and a network of fine red blood vessels. By day 14, a healthy embryo appears much larger and fills most of the egg, making it difficult to see through.
Infertile eggs, sometimes referred to as “yolkers,” appear clear when candled, showing no signs of an embryo or blood vessels. Eggs where the embryo began to develop but then died, known as “quitters,” might show a distinct blood ring or cloudy contents. Removing these non-viable eggs from the incubator is important, as they can spoil, potentially rupture, and contaminate other developing eggs with bacteria, safeguarding the remaining healthy embryos.