|(c) Margaret Gunning|
Two hormones affect the development of spermatozoa: FSH (follicle stimulating hormone) and LH (luteinizing hormone). FSH increases the development of spermatozoa, and LH increases the secretion of androgens from the testes.
Most production-line hens no longer sit on their eggs. This vital trait has been lost during the animal breeding, so the fertilized eggs must be incubated in an automated incubator. The incubation temperature is 37,6 - 38,6 C. Ventilation must allow constant supply of oxygen and removal of CO2. The developing fetus "breathes" since day 1. Air humidity must be 60-70 %, and the eggs must be turned to avoid the fetus from touching the egg shells. Before incubation most eggs are treated with gas. The gas kills 96 % of the bacteria covering the egg shell (dirty eggs can have 50 000 - 200 000 bacteria). If needed, the eggs can also be medicated by dipping them into a liquid medicine.
The fetal cells start dividing within three hours after the internal temperature of the egg has risen above 22 C. The development of a chick proceeds as follows:
- Day 1: a yolk sac is formed, providing nutrients for the embryo. The Embryo weighs 0,0002 g.
- Day 2: The fetal membranes are developed. The heart starts to beat and ears are formed.
- Day 3: Nostrils, feet and wings can be seen.
- Day 4: Tongue starts to form. The fetus weighs 0,05 g.
- Day 5: Genitalia starts to form, the gender of the fetus is developed
- Day 6: The beak starts to develop
- Day 8: The feathers start to develop. The fetus weighs 1,15 g.
- Day 10: The beak hardens
- Day 14: The fetus turns around into a hatching position, head towards the blunt end where it can breathe from the air bubble. The weigh is 9,74 g.
- Day 19: The yolk sac starts to retreat to the chick's abdominal cavity during day 19, and is completely assimilated by day 20.
- Day 21: The chick uses a sharp "tooth" on its beak to break the egg shell, and the bird hatches. The chick weighs over 30 grams.
Growth of chicks and young chickens
The sex of the chick can be determined during the first three days after hatching. Male chicks are deemed useless and destroyed, usually by crushing . Chicken sexing is done manually, and can be very painful for the bird.
Egg and meat chicken producers byu their animals in batches (flocks). Therefore the breeders must make sure that each bird in a flock grows evenly: 90 % of the birds should weigh +- 10 % of the eaverage weight of the flock. Chicks are weighed 2 or 3 times between 5 and 15 weeks of age to assure even growth. In practice a selected sample will be taken and weighed, since each flock may have tens of thousands of birds. Young birds are also vaccinated. The light/dark program and light intensity are very important for young animals. If they will be raised in a poultry house with roosts, the chicks should be allowed to roost already at a young age.