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In developmental biology, the Hamburger–Hamilton stages (HH) are a series of 46 chronological stages in chick development, starting from laying of the egg and ending with a newly hatched chick. It is named for its creators, Viktor Hamburger and Howard L. Hamilton.
Figure 1. Feathering types in ten-day-old chicks.Left: Fast normal-feathering chick. Right: Delayed-feathering chick carrying sex-linked K gene. Delayed-feathering in chickens is a genetically determined delay in the first weeks of feather growing, which occurs normally among the chicks of many chicken breeds and no longer manifests itself once the chicken completes adult plumage.
In the first week of a broiler's life, it can grow up to 300 percent of its body size. A nine-week-old broiler averages over 9 pounds (4 kg) in body weight. At nine weeks, a hen will average around 7 pounds (3.2 kg) and a rooster will weigh around 12 pounds (5.5 kg), having a nine-pound (4 kg) average. Broilers are not raised in cages.
Mass production of chicken meat is a global industry and at that time, only two or three breeding companies supplied around 90% of the world's breeder-broilers. The total number of meat chickens produced in the world was nearly 47 billion in 2004; of these, approximately 19% were produced in the US, 15% in China, 13% in the EU25 and 11% in Brazil.
As is the case with chickens, various breeds have been developed, selected for egg-laying ability, fast growth, and a well-covered carcase. The most common commercial breed in the United Kingdom and the United States is the Pekin duck , which can lay 200 eggs a year and can reach a weight of 3.5 kg (7 lb 11 oz) in 44 days. [ 34 ]
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The coalescence of the neural folds occurs first in the region of the hind brain, and from there extends forward and backward; toward the end of the third week, the front opening (anterior neuropore) of the tube finally closes at the anterior end of the future brain, and forms a recess that is in contact, for a time, with the overlying ectoderm ...
The most distinctive feature of the Cochin is the excessive plumage that covers leg and foot. The skin beneath the feathers is yellow. In the United Kingdom the recognised colour varieties, for large fowl only, are black, blue, buff, cuckoo, partridge and grouse, and white; [3]: 90–93 Cochin bantams are not recognised by the Poultry Club of Great Britain.