The domestic chicken (Gallus gallus domesticus) descends from the wild Southeast Asian species Gallus gallus, also known as the red junglefowl. Domestication dates back approximately 8,000 years, first in China and India, before spreading to the Middle East, Europe, and the rest of the world. Modern laying breeds are the result of intensive genetic selection, started in the 20th century, to maximize egg production.
ensuring good health and adequate longevity. It differs significantly from that of meat breeds (broiler chickens).
Adult laying hens generally weigh between 1.5 kg and 2.2 kg. Their plumage is usually dense and smooth, often brown, white, or reddish in color, depending on the strain. It provides important thermal insulation, as chickens are sensitive to cold and heat stress.
Sexual maturity is reached between 16 and 20 weeks, depending on the strain and farming conditions. Egg laying is triggered by increasing photoperiod, requiring at least 14 to 16 hours of light per day.
Hens lay between 280 and 320 eggs per year, depending on the strain and conditions. The cycle for producing a single egg lasts about 24 to 26 hours and takes place only in the left oviduct. The laying period typically lasts between 72 and 80 weeks, after which production declines. Hens can lay eggs even without a rooster, but the eggs will be unfertilized.
Chickens are highly hierarchical animals. Pecking is a natural behavior in poultry, used to explore, interact, and establish social relationships. However, when excessive or aggressive, it can lead to injury, stress, or even death.
Pecking is closely tied to chickens’ social structure. These animals naturally live in organized hierarchies called pecking orders. Each individual knows its rank, which regulates access to food, water, perches, and nesting areas. In unstable groups, dominance conflicts can cause excessive pecking.
The reproduction of laying hens can be natural or artificial, although in the industry, it is primarily managed through artificial insemination or controlled breeding with selected roosters.
Hens from high-laying strains usually do not brood, due to the loss of maternal instinct. Fertilization is internal, and the rooster’s sperm is stored in sperm storage tubules, allowing for multiple fertilized eggs after a single mating.
Eggs intended for hatching are incubated artificially at 37.5 °C with controlled humidity for 21 days.
In farming, nutrition plays a key role in productivity and the health of laying hens. During chick growth, a high-protein diet (18–20%) is essential. During the laying phase, a high intake of calcium is necessary for shell formation. A laying hen drinks between 200 and 300 ml of water per day, more during hot weather.
In natural settings, chickens are primarily omnivorous. Their varied diet includes seeds, plants, small invertebrates, and insects. They voluntarily ingest grit to help grind food in the gizzard, a muscular organ essential for mechanical digestion.
