| ||The following can be used as a guide in determining whether eggs are fertile, infertile, or if early embryonic death has occurred. In using this guide remember that the descriptions and diagrams are of 'typical" infertile germinal discs, and fertile and early dead embryos. However, their appearance may vary from egg to egg, and may not look exactly as shown and described. It will take some practice and experience to become comfortable with distinguishing between infertile and fertile eggs. The following information is simply a guide.
The germinal disc is the area of the egg where sperm enter into the egg (Figure 1). This is the area of the egg which will form the embryo. The disc is 2-3 mm in diameter.
When the egg is not fertilized, the germinal disc is called a blastodisc (Figure 2). There are four main characteristics associated with an infertile germinal disc:
1. the germinal disc is a solid white spot on the yolk.
2. the germinal disc is not uniform. It is somewhat circular but has "jagged" or "ruffled" edges.
3. the disc is about 2-3 mm in diameter.
4. many vaculoes (bubbles or holes) may be found around the edge of the disc. Sometimes vaculoes are present inside the disc.
When the egg is fertilized, the germinal disc is called a blastoderm (Figure 3). There are four main characteristics associated with a fertile germinal disc:
1. the germinal disc is faint: Not a solid white spot. The germinal disc consists of a faint white ring which may have a solid white spot in the center of the ring.
2. the germinal disc is about 2-3 times larger (5 - 9mm) than the infertile germinal disc.
3. Usually, there are no vacuoles visible in the center of the ring. A few vacuoles may be present on the edge of the ring.
4. the edge of the germinal disc is very smooth and uniform. Ring is predominantly circular with no "jagged" edges
Early dead embryos
Early dead embryos (Figure 4) are similar in shape to the infertile germinal disk. The differences include:
1. the germinal disk is a mixture of solid and faint white areas.
2. the germ spot is approximately the same size as the blastoderm.
3. usually there are many vacuoles visible on the edges of the germinal disc and in the center of the germinal disc.
4. the germinal disc is not uniform. Has irregular edges and is usually not circular in shape.
The appearance of the germinal disc may vary from egg to egg. Eggs which are fertile may not have blastoderms which look exactly the same. The same holds true for the blastodiscs of infertile eggs.
G. M. Fasenko, University of Alberta
Poultry Research Centre News - Vol. 7 No. 1, May 1998