Incubation and Embryology - University of Illinois

Incubation and Embryology Questions and Answers

The following is a list of questions and answers frequently discussed in the incubation-embryology short course. They are arranged by major subject headings.

Poultry Industry and Production Questions | Breeds of Chickens | Egg Grading and Candling | Incubation | Embryology

Poultry Industry and Production Questions

1. Why do brown shelled eggs cost more than white shelled eggs?

Brown shelled eggs cost more because the chickens that produce these eggs eat more feed and production costs are more.

2. Why are brown shelled eggs bigger than white shelled eggs?

Brown shelled eggs are bigger than white shelled eggs because they are produced from a dual purpose breed (eggs - meat) that is larger in size (6-7 lbs.) than a Leghorn breed that is smaller in size (3-4 lbs).

3. Does the time of the year affect the fertility rate?

Extreme cold (winter) or extreme heat (summer) can lower fertility rate dramatically.

4. How many females can one male service?

One male egg producing chicken (Leghorn) can service 10 - 15 females. One male dual purpose chicken (Rhode Island Red) can service 6-8 females.

5. What is the average life of the male chicken?

A male chicken would live on the average of 3-5 years.

6. How large are female chickens?

A female White Leghorn is about 4 lbs. and a female Rhode Island Red is about 6-7 lbs.

7. How can you tell a hen from a rooster?

Difficult to tell at hatch unless they are feathersexed (female primary feathers are longer at 3-4 days of age). In adults, males are larger with longer wattles and larger combs.

8. Do you need sunlight to formulate hard shells on eggs?

No. An adequate source of calcium in the diet is needed.

9. Do chicken houses need to be heated?

No. Usually chickens in large commercial houses provide their own heat.

10. How much light is needed in the chicken house?

Only enough light is needed to read a newspaper at arms length (about 1 foot candle).

11. When does production begin?

At sexual maturity. This is about 17-18 weeks of age for the female hen.

12. What factors affect egg production?

Many factors affect egg production. The most important are diet (nutrition), temperature, humidity, length of artificial light (14 hours of constant light is recommended), and other nutritional and environmental factors.

13. How long does it take to raise a fryer?

About 42-49 days; six to seven weeks to market weight of 4.5 lbs.

14. What is a blood spot?

A blood spot occurs from a broken blood vessel across the stigma line on the yolk follicle when the yolk is released into the reproductive tract.

15. What is a meat spot?

A meat spot occurs when a part of the oviduct peels off when the egg is formed.

16. Is there one kind of egg carton that is better than another?

A styrofoam carton is preferred to a paper carton because it protects the eggs better.

17. How long does it take to put the shell on the egg?

It takes about 20-22 hours for the shell to be deposited around the yolk and albumen. This occurs in the uterus or shell gland.

18. What is salmonella?

Salmonella is a bacteria that can form on the outside of the shell when an egg or its contents become contaminated. It can cause food poisoning if eggs are not properly handled and cooked.

19. What are the critical issues related to salmonella?

Eggs and other food should be properly handled and cooked. Salmonella poisoning is not a problem if food products are properly prepared.

20. How often are eggs infected with salmonella?

It has been shown that possibly one egg in one million eggs produced may have some salmonella growing inside an intact egg.

21. What is the proper way to cook an egg?

Eggs can be cooked in many different ways. Thoroughly cooked eggs include: eggs cooked until the whites and yolks are not runny, hard-cooked eggs, baked eggs, and other egg-rich foods cooked to an internal temperature of at least 106 degrees F.

22. Do brown eggs have more cholesterol than white eggs?

Brown and white shelled eggs have the same amount of cholesterol (200-210 mg per egg).

23. How many eggs does a chicken lay per year?

250-270 eggs per year.

24. What causes a double yolk egg?

The release (ovulation) of two yolks from the ovary simultaneously. It is abnormal and does not occur very often, but will occur in a hen's egg production cycle.

25. Is the shell hard or soft when laid?

The egg is hard when laid by the hen.

26. How is the egg fertilized?

When the rooster inseminates the hen, the male sperm swim up the reproductive tract and localize in sperm host glands in the infundibulum. When a yolk is released one sperm penetrates the germmal disc and fertilization has begun.

27. When do the chicks need water?

Immediately. The chicks need to drink water when they are transferred to the brooder box.

28. When do they need food?

The chick needs food probably the first day, but can survive for up to 3 days after hatching.

29. What are hackle feathers?

Hackle feathers are neck feathers on a chicken. A rooster has long pointed ones, and the female has short rounded ones.

30. What are saddle feathers?

Saddle feathers are feathers toward the tail end of the chicken. A rooster has long pointed ones, and the female has short rounded ones.

31. Can you tell the sex of the chicken from the feathers alone?

Yes, if the breed is feathersexed. The female chicks' primary feathers will be longer than the males. It is difficult to tell the sex of a newly hatched chick if the breed does not have the feathersexed characteristic.

32. Is there a pecking order?

Yes, within a group of chickens from two to hundreds they establish a pecking order of dominance.

Breeds of Chickens

33. Why are brown shelled eggs bigger than white shelled eggs?

Brown shelled eggs are bigger than white shelled eggs because they are produced from a dual purpose breed (egg-meat) that is larger in size (6-7 lbs.) than a Leghorn breed that is smaller in size (3-4 lbs).

34. How do you know what color shell the eggs will have?

The earlobes of the chicken dictate the color of the shell (white ear lobes = white eggs; red earlobes = brown eggs).

35. What kind of chicken lays green eggs?

An Aracona chicken lays green shelled eggs.

Egg Grading and Candling

36. What is the weight of jumbo, extra large, large, medium, small and pee wee eggs?

Jumbo - 30 ounces per dozen
Extra Large - 27 ounces per dozen
Large - 24 ounces per dozen
Medium - 21 ounces per dozen
Small - 18 ounces per dozen
Pee Wee - 15 ounces per dozen

37. What are the egg grades?

Egg grades are:

  • AA - shell-clean, air cell-1/8" or less in depth, white-clear and firm;
  • A-shell-clean, air cell 3/16" in depth, white-clear; and
  • B-shell-clean to slightly stained, air cell over 3/16" deep, white-weaker and watery.

38. What is a leaker?

A leaker is a broken egg where the contents leak out of the shell.

39. What is candling?

Candling is shining a bright light near the egg to determine the egg quality and also embryonic development.

40. When should the eggs be candled?

Eggs can be candled anytime after about Day 5 of incubation through Day 17.

41. How many eggs should be candled at a time?

Out of 2 dozen eggs in the incubator, probably no more than 5-7 eggs should be candled at one setting.

42. How long should the eggs be out of the incubator?

No more than 5 to 10 minutes at a time.


43. What is the best temperature for storing eggs?

Egg should be stored between 55 and 60 degrees F.

44. How much humidity is needed? Enough humidity is needed to maintain a wet bulb temperature of about 85 to 87 degrees F (50-55 percent relative humidity). This is normally attained if water channels in incubator are kept full.

45. How do you disinfect the incubator?

Disinfect incubator with 10 percent bleach solution, then wash with warm soapy water and rinse thoroughly.

46. Does when the egg was laid affect the hatch date?

No. If fertile eggs are stored properly (55-60 degrees F) then hatch date for the chicken will be about 21 days following the time they are placed in the incubator.

47. When should the incubator be prepared for the eggs?

About one week before starting the incubation process.

48. Where should the eggs be stored, if they cannot be set right away?

If they cannot be put in an incubator right away, then they should be kept in a cool room at a temperature of 55-60 degrees F.

49. What is the longest eggs should be held before incubating?

No more than seven days.

50. What is the correct temperature for incubating fertile eggs in a still air incubator?

Optimum temperature is 100.5 degrees F.

51. What is the temperature range that is acceptable during incubation?

Temperature range is 99 -103 degrees F.

52. What is the lowest temperature?

Lowest temperature should be 99 degrees F.

53. What is the highest temperature?

Highest temperature should be 103 degrees F. Never keep at 103 degrees F for more than than a few hours.

54. How do you check the accuracy of the incubator thermometer?

Accuracy of an incubator thermometer can be checked by placing a medical thermometer and an incubator thermometer in a pan of 100 degree F water, or take a good thermometer from the science storeroom and place it next to the incubator thermometer in the incubator at 100 degree F.

55. When should the plugs be removed from the incubator?

Remove plugs (air holes) from the top of the incubator when you see the chicks start to hatch.

56. What are the factors for success?

Successful hatches can be obtained by:

  • Securing fertile eggs
  • Maintaining the correct temperature
  • Maintaining correct humidity levels
  • Increasing ventilation when chicks hatch
  • Turning the eggs properly

57. What should be used to mark the eggs?

A lead pencil only.

58. Do I need to take the eggs home for the weekends?

Yes, it is encouraged to take eggs home on the first two weekends to turn the eggs and regulate temperature.

59. How do I transport the incubated eggs from school to home and back?

Carefully. Put the eggs in a styrofoam egg carton and wrap the carton in a blanket; or leave eggs in the incubator and place a blanket over them so they won't roll around.

60. Where should the eggs be placed in the car when taking them home?

Place the eggs on the front floor on the passenger side and turn on the heat.

61. What is the normal hatch time for a fertile incubated egg?

Normal hatch time for chicken eggs is 21 days.

62. What will delay the hatch?

Too low of an average temperature will delay the hatch.

63. Why are the chicks sometimes very wet and mushy?

Chicks are wet and mushy if too much humidity is in the incubator. To lower humidity at the end do not place more than one sponge in bottom of incubator.

64. How can I be sure that I have enough humidity?

If the proper water level is maintained in the bottom of the incubator the correct humidity should be maintained.

65. How can I tell if I have too much humidity?

If there is a lot of condensation on the inside of the incubator windows, then there is probably too much moisture in it. This is usually not a big problem.

66. How long should I leave the eggs in the incubator if they do not hatch on the twenty-first day?

Leave the unhatched eggs until the 23rd or 24th day.

67. What causes deformed legs?

Deformed legs are caused by poor nutrition of the hen. Other factors are disease, contamination and improper temperature.

  68. How do I add water?

Add warm water (100 degrees F) with a squeeze bottle, or meat baster; do not get eggs wet.

69. How do I count the days?

Count the days of incubation from the first day the eggs are placed in the incubator. If placed in the a.m. that day would be Day 1; if placed in the p.m. that day would be Day 0, the next day would be Day 1.

70. When do I stop turning the eggs?

Stop turning the eggs on Day 18.

71. When should I put the crinoline on the wire grate?

Put the crinoline (cheese cloth) on the wire grate of the incubator after Day 17 or on Day 18.

72. How can I add additional humidity?

Add additional humidity on Day 18 by placing 2-3 wet sponges on the bottom of the incubator.

73. What should I do if the chicks do not fluff up?

If chicks do not fluff up remove sponges from the incubator and water from the channels.

74. What is the brooder box?

A brooder box is a temporary home for baby chicks up to one week of age. It contains 2-3 inches of litter, a feeder, and water. It also includes a heat source suspended above the box.

75. How do I make a brooder box?

Take a cardboard box (2' x 3' x 1') and place items mentioned in answer 74.

76. What should be used in the bottom of the brooder box?

Use soft pine-wood shavings, untreated cat litter, sand, rice hulls, or ground corn cobs, but not newspaper.

77. Do the teachers need to teach the chicks to drink and eat?

Yes, it would be a good idea to dip the baby chick's beak in the feed and water so they know where it is.

78. Should you help a chick out of the shell?

No, if the chick can not come out of the shell on its own then it is a weak chick and probably would not survive.

79. Where should the thermometer be placed in the incubator?

On the wire grate away from the heat source and in the center of the incubator.

80. What is the function of the air cell?

The air cell function is to provide the chick with air when it first starts to break open the shell.

81. What is the critical period in hatching?

The first 3-5 days and Days 18 and 19. When the embryo is forming early on and when it gets in position to hatch.

82. How often should the eggs be turned?

Eggs should be turned at least three times a day.

83. What happens if the eggs are not turned?

If eggs are not turned, the embryo will die about Day 11.

84. What causes the embryo to develop fully, but not pip the shell or hatch?

Too low or too high temperature, to too low or too high humidity.

85. Do you need to do anything to prevent the chicks from drowning?

Place marbles or rock in the water pan in the brooder box to keep chicks from drowning.

86. Why do chicks stick to the shell?

Too low humidity during incubation.

87. What causes the navel to be sore?

Too high temperature during incubation, excessive humidity near the end of incubation, or infected embryo early in incubation.

88. What should you do if the chicks pick at one another?

Separate them from each other in the brooder box, or construct another brooder box and separate the chicks.

89. Can chicks be marked?


90. How do you color embryos?

To color embryos you inject a colored dye about .2 to .5 milliliters into the egg with a hypodermic needle near the bottom of the egg.


91. How do you preserve embryos? Using formalin or glycerine and ethyl alcohol?

Embryos can be successfully preserved by storing them in an alcohol solution (3-4 drops of glycerine on embryo), then immerse in 70 percent alcohol (14 parts of 95 percent ethyl alcohol to 5 parts of water).

92. What is the correct procedure for breaking out an embryo?

Break open the shell on the large end of the egg, then pour out the liquid contents and carefully drop the embryo on a pie tin.

93. How long does it take to pip the shell completely?

Two to four hours.

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