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