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1. What happens when a chicken hatches?
2. This is what you already know. An egg is a single cell.
An egg has 1 set of chromosomes. (1n)
After the rooster goes into the henhouse. . .
The eggs have 2 sets of chromosomes (2n)
The egg is now called a zygote.
3. Some vocabulary The word EGG is a generic word with different meanings.
We always think of an unfertilized chicken egg,
Sometimes it is fertilized (a zygote), but we still call it an egg.
It can also mean an immature cell, without a shell, called an oocyte
4. Egg development It takes a hen about 25 hours to make an egg.
A hen only has her left ovary and it has about 4000 oocytes, each enclosed in a tiny sac. . .
When a sac ruptures, an oocyte enters the oviduct funnel
5. The funnel is connected to the oviduct.
The oviduct is an 80cm long tube
That is divided into 5 parts.
The next slide names the parts, tells how much time the egg spends in each, and what happens in each part.
6. Oviduct parts
7. Laying an egg.
8. A little different Chickens, as well as other birds, have a common opening for reproduction and the removal of stools and urine.
This opening is called the "vent"
They do not have a bladder because their urine is not a fluid. It is a white paste, called urates, that you can observe surrounding the droppings.
9. Cloaca The intestine, ureters and oviduct come together into a common chamber called the cloaca.
This is a dirty place, whereas the egg is always clean and almost sterile when laid.
10. Laying an egg. The hen turns part of the cloaca and the last segment of the oviduct inside out, "like a glove.
The red membrane sticks way outside of these organs.
11. Red membrane
12. Clean eggs The egg emerges far outside, at the end of the bulge.
It cannot contact the walls of the cloaca and get contaminated by stools or urine.
The intestine and inner part of the cloaca are kept shut by the emerging egg, and their contents cannot leave when the hen strains to deliver the egg.
13. Dirty eggs Eggs are always clean as they are laid.
However, sometimes a hen, stomping around the nest with dirty feet, will get the egg dirty anyway.
Sometimes chickens get pretty angry. See video next slide
14. Sometimes chickens get pretty angry.
15. OK to eat Its ok to eat dirty eggs, but they cant be cleaned off for hatching.
16. Stages in embryo development
17. Before the egg is laid Fertilization.
Cleavage (Zygote divides).
Cells segregate into groups of specialized function (nerves, blood vessels, etc.)
The embryo nearly stops growing between laying and incubation
18. Day 1 - last 7 hours 18 hours: The alimentary tract appears.
19 hours: The brain begins to form.
20 hours: Somites appear.
21 hours: The nervous system begins to form.
22 hours: The head begins to form.
23 hours: Blood starts to form.
24 hours: The eyes begin to form.
19. Day 2 - major events 25 hours: The heart begins to form.
33 hours: The ears begin to form.
42 hours: The heart starts to beat.
20. Day 3 - major events The head begins to turn onto its left side.
The tongue begins to form.
The amnion completely surrounds the embryo.
The tail appears.
Wing and leg buds are visible.
Soon other organs such as the liver, kidneys, and lungs will appear.
21. Day 4 - major events The somites extend to the tip of the tail.
The toes begin to form.
The allantois is visible.
Label this drawing
22. Day 5 - major events The reproductive organs begin to form.
The bones of the legs begin to form.
The crop begins to form.
23. Day 6 - major events The beak becomes visible.
The wing bends at the elbow.
The allantois fuses with the chorion.
The ribs begin to appear.
The gizzard begins to form.
The intestines begin to loop.
24. Day 7 - major events A row of feather germ cells appears on the tail.
The sclera of the eye begins to form.
Feather papillae appear on the thigh.
The leg bends at the knee.
25. Day 8 - major events Three rows of feather germs are visible on the tail.
The nictitating membranes (inner eye lids) begins to form.
The egg tooth begins to form.
The bone marrow cavity of the femur begins to form.
26. Day 9 - major events Upper eye lids begin to cover the eyes.
The knee caps begin to form.
27. Day 10 - major events Claws begin to form.
The comb is visible.
Flight feathers appear.
Feather tracts appear over the sternum.
Lower eyelids develop.
28. Day 11 - major events The toe claws begin to curve downward.
The bottom of the feet become padded.
Feather germs on the back and tail appear as long, tapering cones.
The beak begins to harden.
The comb appears serrated.
The embryo begins to draw calcium from the eggshell for its growing bones.
29. Day 12 - major events Scales appear on the lower legs.
The embryo continues to grow and move.
The ribs begin to turn to bone.
30. Day 13 - major events Fingers of the wings are covered with feather papillae.
The left and right collar bones fuse to form the wishbone.
31. Day 14 - major events The embryo turns its head toward the blunt end of the egg.
The skull has begun to ossify.
32. Day 15 - major events The scales, claws, and beak are becoming firm
33. Day 16 - major events The embryo turns its beak toward the air cell.
The chorion lines most of the inside surface of the egg shell.
34. Days 17-21 - major events Day 17: The beak turns towards the air cell.
Day 18-19: The beak breaks through the inner shell membrane.
Day 18-19: The lungs begin to function.
Day 19: The yolk sac begins to enter the body cavity.
Day 20: The lungs are using the air cell for breathing completely.
Day 20: The embryo occupies all of the egg except air cell.
Day 21: The neck begins to spasm.
Day 21: The egg tooth pips through the shell.
Day 21: Exhausted and wet - but alive - the chick has hatched!
35. Video of hatching chick
36. Candling an egg http://shilala.homestead.com/candling.html
37. More candling
38. Still more candling
39. Embryos From your questions, you already know the following has happened before the egg is even laid:
The egg is fertilized.
The zygote divides and begins to grow.
The cells segregate into groups of specialized function.
So, at the end of the 1st day, it is really Day 2
Sort of like you were . . . .
How old were you on your 1st day?
1 day and 9 months.
40. Drawings and photos The following slides show drawings and photos at various stages.
41. Day 5
42. Day 7
43. Day 10
44. Day 15
45. Day 20
46. 24 hour embryo
47. 33 hour embryo
48. 48 hour embryo
49. 72 hour embryo
50. Link to many pictures of embryos http://www.swarthmore.edu/NatSci/sgilber1/DB_lab/Chick/chick_stage.html
Link to cross-section pictures
http://nte-serveur.univ-lyon1.fr/nte/embryon/www.uoguelph.ca/zoology/devobio/24hrchck/24ck12.htm
Select best egg for incubating game.
51. Links Incubation instructions
http://www.ext.vt.edu/pubs/poultry/factsheets/8.html#L1
Link to mating http://www.users.on.net/~greggles/reproduce.html
Everything chicken http://www.angelfire.com/oh/ZebraDirectory/chickinfo.html
52. END
53. Amnion One of the membranes that surrounds the chick embryo
Bag of waters surrounds embryo.
What breaks before a human baby is born.
54. Somites Look like bones in the embryo.
Actually develop into
SKIN
MUSCLES
VERTEBRATE
55. Allantois A lung in chicks
Part of umbilical cord in mammals
56. Chorion
57. Feather papillae Early
Late develop into feathers
