Poultry farmers examine the eggs against the light to see which ones have been fertilized and will become chicks. The backlight examination can also reveal if there are problems with the development of the embryo or if development has stopped. This procedure requires that the egg is illuminated so as to reveal what is contained within it. This article explains how to proceed correctly.
Steps
Method 1 of 2: Understanding the Technique
Step 1. First of all you need to know why the backlight exam is performed
If you breed poultry you should monitor the development of the eggs to know their development, which is difficult but feasible thanks to this procedure. The examination consists in projecting a strong light on the surface of the egg, which must then be observed against the light to see its contents and establish the degree of development.
- In domestic farms you never get 100% fertile eggs that develop to the end. Some eggs are not fertilized from the start, while for others development stops during incubation.
- It is important to recognize and remove eggs that are not developing properly, so as to prevent them from rotting and breaking, contaminating other eggs with bacteria and unpleasant odors.
Step 2. Use the correct equipment
No complex or specific tools are needed, in fact this analysis in the past was carried out simply in the light of a candle. The most important thing is a fairly intense light source (the higher the intensity, the better the result), with an opening smaller than the diameter of the eggs to be analyzed. The examination should be performed in the dark, to better observe the inside of the eggs.
- Farm and livestock equipment dealers generally provide tools for this exam; it is usually a kind of battery-powered or fixed-power flashlight.
- You can also create your own dedicated instrument by inserting a 60 W bulb inside a jar on which you will have drilled a hole with a diameter of 2-3 cm. Alternatively, get a very bright pocket flashlight, and possibly cover the head with a cardboard with a hole of the diameter already specified.
- There are specific and more expensive machines to achieve the same result, equipped with a rotating support, curtains that block the external light, and the possibility of enlarging the view by means of lenses.
Step 3. Schedule the egg check
The first time you should examine the eggs before you even put them in hatching or in the incubator. Even if you don't see anything and can't tell the fertilized eggs from the ones that aren't, examining them at first gives you a good reference of what the eggs look like against the light, and can be used to compare the eggs you will examine later.
- It is also useful to check if the eggs have cracks or fissures that are not visible to the naked eye. Cracked eggs are more easily attacked by bacteria that can damage the embryo during development. If you find cracked eggs, do not eliminate them but keep them under control for the following days.
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Although some check the eggs daily during incubation, it is a good idea to wait up to seven days from the start of hatching for the first check, for at least two good reasons:
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Number one:
Eggs are sensitive to temperature changes, and moving them often outside the incubator could compromise their development, especially in the early stage.
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Number two:
In the first week the embryos develop little, and it would be very difficult to distinguish between the fertilized eggs and those that are not.
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- After examining the eggs on the seventh day, leave them in the incubator until day 14. At this point you will be able to verify if the eggs whose development was uncertain are fertilized or not, eventually eliminating them from hatching.
- After 16 or 17 days, you should avoid further examining the eggs, because in the period immediately before hatching it would be better not to move or turn them. Furthermore, at this stage of development the embryos have grown and show almost nothing on the backlit examination.
Method 2 of 2: Examining Backlit Eggs
Step 1. Hold the egg against the light source
Place the analysis space in a dark environment near the incubator. Take one egg at a time and hold it up close to the light source. Proceed like this:
- Bring the larger end (where air is contained) close to the lamp. Grab the egg with your thumb and forefinger, holding it by the narrow end. Tilt the egg on its side and rotate it until you have a correct view.
- As you do this, you should mark each egg with a number, and make a note of what you observe, so that you can compare the results of each test.
- Work quickly, but be very careful not to drop the egg. The eggs must be reintroduced into the incubator within 20 or at most 30 minutes, in order not to risk damage to the embryos. Even in nature, the hen moves away from hatching for frequent but short periods.
- Eggs with a dark or mottled shell are more difficult to analyze because less light shines through in these cases.
Step 2. Look for signs that the egg is developing an embryo
The telltale signs are as follows:
- There are visible traces of blood vessels that branch out from the center.
- With less intense light, you should distinguish between a more transparent part where the air sac is located, and a darker part where the embryo develops.
- With good technique and sufficient experience, you should be able to distinguish the dark outline of the embryo, placed in the center of the blood vessels. You should also be able to distinguish the eyes, which are the darkest spot on the embryo.
- If you're lucky, you might even watch the chick move!
Step 3. Look for signs that the egg is not developing
Some embryos stop developing for various reasons, including changes in temperature or humidity, pathology or other unfavorable conditions.
- The most obvious sign that an egg is not developing properly is the presence within a circle of blood. This circle is an obvious sign, clearly visible inside the shell, and is formed when the embryo has died and the blood vessels that supported it move away from the center, settling on the edges.
- Other signs include the formation of spots or streaks of blood inside the shell. These spots can be difficult to distinguish from healthy embryos in the first few days of development.
- If you are sure that the embryo has died (for example by observing the circle of blood described above), you can eliminate the egg immediately to prevent it from rotting and contaminating the other eggs contained in the incubator.
Step 4. Look for signs that the egg is unfertilized
If it has not been fertilized, the egg cannot develop an embryo. To identify these eggs do the following:
- The egg looks exactly the same as it did during the first check, when you placed it in the incubator.
- The inside of the shell appears transparent, with no signs of darker areas, blood vessels, or circles of blood.
Step 5. If unsure, leave the eggs where they are
If you believe that you have identified an unfertilized egg but are not completely sure, do not eliminate it immediately, to avoid throwing away eggs that can develop an embryo.
- Mark the uncertain eggs, and leave them in the incubator, to give them a second chance.
- Check again for uncertain eggs on day 14. If they still show no obvious signs of development, or if they have a circle of blood, you can discard them.
