Answers to Commonly Asked Embryology Questions

1. Can two chicks hatch from one egg?

Yes. It is a rare occurrence. When two chicks hatch from the same egg, the egg usually has two yolks. Usually, one embryo out competes the other and only one chick survives to hatch. Many time both embryos die before hatch.

We have no knowledge of Siamese twin chicks ever being hatched. The development of twin chicks from a single-yolked egg.

2. What is a double-yolked egg?

It is an egg which has two yolks in it. Both yolks were ovulated (released) at or about the same time and enclosed in the same shell. Many eggs with double yolks occur when young adult female chickens first start producing eggs. Their egg-forming organs are not adjusted or not yet synchronized, so two yolks are released together. Shortly after egg production starts, the chickens' bodies adjust, and for the most part, they then lay eggs with only one yolk. But, there are some chickens which inherit the characteristic to lay double-yolked eggs and usually continue to do so throughout their life.

3. If a female chicken is hatched with about 4,000 ova and lays only 240 to 250 eggs a year, what happens to the remainder of the ova?

Depending on the state of health and condition of the chicken they can: (1) continue to exist in the hen's body ready to form a yolk, or (2) they can be absorbed by the hen's body.

4. Can I hatch the eggs I buy at the store?

No, the eggs in grocery stores are infertile and will not hatch unless they come from a special farm that niche markets fertilized eggs.

The male does not need to be present for the hen to lay eggs.

5. If I find a bird egg, such as a robin's egg, can I hatch it?

It is possible, but you should not because young birds, like the robin, require the skilled care of its parents to survive. People cannot provide the same kind of care, and the baby bird will most likely die from starvation, cold, or mismanagement. They need to be fed crop milk hourly for weeks.

It is also illegal in many states to collect wild bird eggs.

6. If a mother hen sits on a fertile egg, will it always hatch? If not, what does she do with it?

Not all fertile eggs will hatch, even when incubated either by a broody hen or in an incubator. Under some conditions they will contain weak or defective embryos. Hatchability is influenced by (1) age of eggs at setting; (2) conditions under which they were hold before incubation; (3) parent stock, including its breeding potential, health and diet; and (4) conditions while the eggs are being incubated. So, the fact that a hen is doing the incubating does not guarantee that a fertile egg will hatch. If an egg or eggs do not hatch, the hen eventually leaves them and the nest. She leaves because the hormone that caused her to go broody is no longer secreted, so she stops setting on the eggs. In a way, it could be said that nature has told her to quit.

7. How long can the mother hen be off the nest during the day? What will happen if she stays off too long?

A setting hen can be off the nest 15 to 20 minutes or a little longer at one time without harming the embryos, unless the weather is extremely cold. If she remains off too long, the embryo will be chilled. Then, some of the chicks may be weakened, and some of the embryos will die and not hatch.

8. If an embryo dies during incubation, does it feel pain?

In most cases, no. The embryo just goes to sleep. In the case of severe jolting, extreme heat or cold, and similar causes of death, the embryo might experience some discomfort depending on the stage of development.

9. Why does the eye get so big and why does it grow so fast?

We do not have the exact answer to this. However, it is possible that both size of the eye and speed of its growth could be at least partially due to the eye being so very complex and so important. Thus, considerable time is needed to completely form and develop it. Also, organs that involve the development from multiple cell layers take longer to form.

10. Can you open the shell for the chick?

Yes but it is not recommended. There is usually a good reason why the chick can not hatch by itself. The chick is usually weak, deformed or has other physical problems. If you aid the chick in hatching it may be painful to the chick and the chick usually will die.

The youth can come to understand the chick not hatching naturally. However, if you help (not matter how good the intention) the results will be viewed as your fault.

11. Can we hold the chicks as soon as they hatch?

Before the chicks are handled, the hatched should be completed, and the chicks should be allowed to dry completely and fluff up.

12. How can you tell if the chick is male or female?

Unless you know the strain of birds are sex linked, meaning the males and females are different colors or different feathering rates, you can not tell them apart without special training. Trained chick sexers can tell the difference by examining the chick's internal organs with a magnifying devise. Vent sexing requires you to know that strains expression of folds since a chicken has no organ.

If they are have sex linked feather trait you can tell the difference by (1) different fluff color or (2) observing the difference in the length of the chick's primary wing feathers at one day of age.

13. Can I take the chick home?

No. You should not take the chicks home unless your family or some relatives live on a farm and have the proper equipment and buildings and the knowledge to care for them appropriately.

14. How long after the chick hatched does it become an adult?

Chickens will become sexually mature in about five months. Quail can become mature in as little as six weeks.

15. How long do chickens live?

Broilers reach market age in six to eight weeks. On most commercial egg farms, laying hens have completed their usefulness when they are 18 to 20 months old. Records show that when chickens are allowed to live out their lives naturally, many of them will live in the range of six to ten years, and some claims have been made of some chickens living as long as 22 years.

Written by: Phillip J. Clauer, Senior Extension Associate, Poultry Science Department, Penn State, 2002