Egg

An egg is the organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an ovum. Most arthropods, vertebrates, and mollusks lay eggs, although some do not, such as scorpions and most mammals.

Reptile eggs, bird eggs, and monotreme eggs are laid out of water, and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a favorable temperature range (warm) while the embryo grows. When the embryo is adequately developed it hatches, i.e. breaks out of the egg's shell. Some embryos have a temporary egg tooth with which to crack, pip, or break the eggshell or covering.

The largest recorded egg is from a whaleshark, and was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size; whale shark eggs normally hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird, though the extinct elephant bird and some dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). The eggs laid by some reptiles and most fish can be even smaller, and those of insects and other invertebrates can be much smaller still.

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Poultry farming

Poultry farming is the raising of domesticated birds such as chickens, ducks, turkeys and geese for the purpose of farming meat or eggs for food. Poultry are farmed in great numbers with chickens being the most numerous. More than 50 billion chickens are raised annually as a source of food, for both their meat and their eggs. Chickens raised for eggs are usually called layers while chickens raised for meat are often called broilers. In the US, the national organization overseeing poultry production is the Food and Drug Administration (FDA). In the UK, the national organization is the Department for Environment, Food and Rural Affairs (Defra).

Intensive and alternative poultry farming

According to the World Watch Institute, 74 percent of the world's poultry meat, and 68 percent of eggs are produced in ways that are described as 'intensive'. One alternative to intensive poultry farming is free-range farming using lower stocking densities. Poultry producers routinely use nationally approved medications, such as antibiotics, in feed or drinking water, to treat disease or to prevent disease outbreaks. Some FDA-approved medications are also approved for improved feed utilization.

List of chicken breeds

There are hundreds of chicken breeds in existence.Domesticated for thousands of years, distinguishable breeds of chicken have been present since the combined factors of geographical isolation and selection for desired characteristics created regional types with distinct physical and behavioral traits passed on to their offspring.

The physical traits used to distinguish chicken breeds are size, plumage color, comb type, skin color, number of toes, amount of feathering, egg color, and place of origin. They are also roughly divided by primary use, whether for eggs, meat, or ornamental purposes, and with some considered to be dual-purpose.

In the 21st century, chickens are frequently bred according to predetermined breed standards set down by governing organizations. The first of such standards was the British Poultry Standard, which is still in publication today. Other standards include the Standard of Perfection, the Australian Poultry Standard, and the standard of the American Bantam Association, which deals exclusively with bantam fowl. Only some of the known breeds are included in these publications, and only those breeds are eligible to be shown competitively. There are additionally a few hybrid strains which are common in the poultry world, especially in large poultry farms. These types are first generation crosses of true breeds. Hybrids do not reliably pass on their features to their offspring, but are highly valued for their producing abilities.

Chicken

The chicken (Gallus gallus domesticus) is a domesticated fowl, a subspecies of the red junglefowl. As one of the most common and widespread domestic animals, with a population of more than 19 billion in 2011, there are more chickens in the world than any other species of bird or domestic animal. Humans keep chickens primarily as a source of food, consuming both their meat and their eggs.

Genetic studies have pointed to multiple maternal origins in Southeast-, East-, and South Asia, but with the clade found in the Americas, Europe, the Middle East and Africa originating in the Indian subcontinent. From India, the domesticated chicken was imported to Lydia in western Asia Minor, and to Greece by the fifth century BC. Fowl had been known in Egypt since the mid-15th century BC, with the "bird that gives birth every day" having come to Egypt from the land between Syria and Shinar, Babylonia, according to the annals of Thutmose III.

Terminology

In the UK and Ireland adult male chickens over the age of one year are primarily known as cocks, whereas in America, Australia and Canada they are more commonly called roosters. Males less than a year old are cockerels.Castrated roosters are called capons (surgical and chemical castration are now illegal in some parts of the world). Females over a year old are known as hens and younger females as pullets although in the egg-laying industry, a pullet becomes a hen when she begins to lay eggs at 16 to 20 weeks of age. In Australia and New Zealand (also sometimes in Britain), there is a generic term chook /ˈtʃʊk/ to describe all ages and both sexes. The young are called chicks and the meat is called chicken.