you are anticipating the arrival of shipped eggs, you should have your
incubator plugged in at least two to three days in advance and be sure
that the temperature and humidity are correct and stable. It you
wait until the last minute to do this, you may get a surprise you don't
want. During incubation, closely follow the instructions that accompanied
your incubator. Most fowl require a temperature of 99.5 degrees Fahrenheit
and a relative humidity of 55% during the initial period of incubation.
During the last three days of incubation, the temperatures are generally
reduced by one degree and the relative humidity is increased to 65% relative.
Most incubators come with a chart showing the requirements for various
breeds of fowl.
Before the eggs arrive, be sure your thermometer is accurate by comparing it with a second or third thermometer. You may find it advantageous to purchase a battery operated digital readout thermometer/hydrometer. These are available from any Radio Shack store for about $24. They display humidity directly in Relative Humidity, and are much easier to use than trying to get a good wetbulb reading. Be sure your batteries are GOOD. When the batteries begin to weaken in these units, the humidity reading goes way off (this is from experience...) even though the temperature reading is still accurate.
If you receive eggs shipped in the mail, it's a good idea to unpack them as soon as they arrive to determine if there is any damage. After unpacking allow them to "settle" to room temperature for several hours before incubation. It is advisable to candle shipped eggs BEFORE incubation. If you use the packing methods described here, eggs should seldom arrive broken. However if the package was handled too roughly or dropped during shipping, the air sack in the large end of the egg may have been ruptured.
When candled, a ruptured air sack will appear as a floating air bubble inside the egg that always moves to the top as you rotate the egg. If this happens, the egg will almost surely NOT hatch. Inform the person you purchased the eggs from and he may be able to provide a replacement shipment at reduced cost. If the air sack has NOT been ruptured, it will remain stationary at the large end of the egg, and you will be able to detect the yolk as a dark mass roughly in the center of the egg that should remain fairly stationary. Candling will usually also show up any cracks in the shell that may not be detectable to the naked eye. Eggs with minor cracks should normally be discarded. If the egg is valuable and/or not easily replaceable, you could try using clear nail polish to seal the crack. These eggs may sometimes hatch, but as the egg is heated during incubation, the insides will expand and the egg may "ooze", fouling the air in the incubator. If you seal a crack in this manner, be sure to check it frequently during incubation to insure it isn't leaking.
After about 5 days of incubation, the eggs should again be candled to assess fertility and development. A very good low cost candling device is available (Cool-lite Candler, part number 9046) for about $8 from several suppliers including Cutler Pheasant Supply of Applegate, Michigan (810) 633-9450 email: email@example.com.
In the case of white eggs you should be able to detect a faint "weblike" structure of blood veins inside the egg and an overall more reddish tint than an infertile egg. Candling takes a little practice, but you will quickly become accustomed to it. With brown or thick shelled eggs such as guinea eggs, The vein structure may not be noticeable until day 6, 7 or 8. With any egg, you should be able to easily tell the difference by day 8-10 between an egg which has an embryo developing in it and one that does not.