The poultry industry breeds chickens destined for both commercial egg and meat production. Geneticists design special breeding programs to select birds with the best characteristics for egg or meat production. This selection process (called genetic selection or genetics) allows the industry to select strains of birds which are produced very efficiently in intensive housing systems. There are two main types of commercial chicken breeds: layers and meat (broiler) chickens.
The hen releases a yolk with the egg cell in it from her ovary where it moves into the oviduct (egg production tube). When a cockerel and a hen are mated, the sperm cells from the cockerel fertilise the egg cell at the top of the oviduct (fertilisation is the joining of the female egg cell with the male sperm). The fertilised egg yolk then takes 23-26 hours to pass down the oviduct, during which time layers of egg white (albumen) are laid down. Two layers of egg membranes are then overlaid, and finally the egg shell. If an egg is not fertilised, it still goes through the same process in the oviduct but it will not develop into a chick.
Although the surface of the egg is covered with bacteria, it has its own protective mechanisms in place to prevent the bacteria spoiling the eggs. These are:
Most eggs are laid in the morning. Eggs are collected as soon as possible after laying and placed in a cool room to help preserve their internal quality. Fertile eggs can be stored for up to 7 days at about 12-15oC without loss of hatchability. Because of the danger of bacteria on egg shells going to the hatchery, all fertile eggs are fumigated on the farm or as soon as they arrive at the hatchery. Fumigation with the gas formaldehyde kills surface bacteria without damaging the fertilized ovum inside the egg.
The hatchery is a special building with controlled ventilation. It contains machines for holding and incubating large numbers of eggs. The hatchery is designed with hygiene in mind and is laid out so that there is little chance of any contaminating organisms travelling back from hatched chicks to eggs brought in later.
The first stage lasts for 18 days and is called setting. The eggs are placed on special trays which can be tilted through 90 degrees, from side to side. The temperature and humidity of the air in the setter is controlled so that conditions inside each egg are suitable for the growth and development of the chick.
On the 18th day, eggs are transferred to a different tray, which cannot be tilted, and placed in another machine called a hatcher. Eggs are transferred to hatchers so that hatching chicks do not contaminate other batches of eggs being incubated. The hatchers can then be thoroughly cleaned after every hatch. By the end of the 21st day all chicks have hatched and are ready to be removed from the machine. They are taken to a special room and removed from the hatcher tray. They are then placed in chick boxes (usually 100 to a box) ready for delivery to a farm.
Sexing allows separation of male and females chicks. This can be done by:
Layer chicks are always sexed, as the females are kept while the males are killed. Breeders are usually sexed, as only one sex of each breeder strain is kept. Meat chickens are normally left unsexed, as both sexes are usually reared together.
Some vaccines can be administered in the hatchery. Beak trimming is sometimes carried out and in some breeds, the comb of the cockerels is trimmed (called dubbing). These procedures may seem cruel but they are carried out to prevent further injury later in life. Beak trimming is done to prevent pecking other birds, or cannibalism. Dubbing is done to prevent injuries to the comb which can result from fighting.
The baby chick must be kept warm as it does not have the ability to maintain a constant body temperature. The chicks are transported in chick boxes which are designed to conserve heat while allowing air movement. The room where chicks are held in the hatchery and the truck which delivers them to the farm are also designed to keep the chicks both warm and ventilated. There is enough food and water in the yolk to keep the chick alive for about three days, but best results are obtained if they can eat and drink as soon as possible. When placed on the farm, they must be kept warm and have feed and water available at all times.