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From Egg To Chick:

Coloring Chick Embryos


Coloring embryos by injecting dye into eggs before they hatch has been practiced for a number of years. It is done to identify the young of certain hatches or groups. And it makes it easier to observe movements of wild birds (especially water fowl) after they leave the nests.

The process of coloring chicks by injecting dye into the eggs also provides an opportunity to study early feather growth. Juvenile plumage will replace the colored down in about two weeks. As this happens, the dyed background amid new growing feathers provides a constantly changing pattern.

While it is possible to inject eggs from about the 10th to 19th days of incubation, the period from the 11th to 14th days appears to be ideal. Only one treatment is necessary if the injection is done at this time. When injections are made after the 14th day the color usually remains localized because the embryo occupies most of the egg; so it may be necessary to inject the egg in more than one place.

Harmless vegetable dyes, such as food coloring dyes sold in grocery stores, work very satisfactorily. Most of these dyes are sold in concentrations of 2 percent and 3 percent solution and are suitable for direct injection into the egg. No further dilution or sterilization is necessary. Dyeing by injection of the egg will not affect the chick's health, appetite, or growth.

Different colors of dyes can be used. Red, green, and blue usually give the clearest and most distinct results. Yellow and orange vary only in intensity and do not give sharp differences. Different colors can be blended from the primary colors. Best results can be obtained by using naturally white chicks.

When you are ready to make the injections, remove the eggs from the incubator, candle them, and discard any infertile ones or those which contain dead embryos. Work with only as many eggs as you can complete in one-half hour or less. This will avoid excessive chilling. Wipe the small end of each egg with a 95 percent alcohol solution to sterilize the area where the shell will be punctured. Tincture of iodine (2 percent) or merthiolate can be used in place alcohol. Allow the eggs to dry.


Figure 11
Cross section of an 11-day old embryo showing the site of injection. (Fig. 11)

At a point about one-half inch from the small end of the egg (see Fig. 11 ), make a small hole in the shell with a sharp probe, such as a dissecting needle or large hypodermic needle. The hole should be just large enough for the hypodermic needle you use to inject the dye.

Inject about 0.2 to 0.5 cc of dye into the egg with a sterile hypodermic needle and syringe. Use a 22 to 27 gauge needle, 3/8 to 1 inch (.95 to 2.5 cm) long. The amount of dye injected will affect the degree of coloring somewhat. Release the dye gently and slowly (to prevent overflow) just beneath the inner shell membrane. To avoid injury to the embryo, be careful not to penetrate too deeply.

Close the hole in the shell with a drop of melted paraffin, fast-drying cement, collodion, or a piece of plastic tape cut from a Band Aid. Return the eggs to the incubator. If you handle the eggs carefully and use clean techniques, they should hatch in the normal time and rate for the conditions under which you incubate them.

If you wish to do additional reading on coloring embryos, a good reference is "A Method of Color Marking Young Waterfowl," by C. D. Evans, Journal of Wildlife Management, Volume 15, No. 1 (pages 101-103), 1951.



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