FORMATION OF THE YOLK
a. The yolk (see figure. 1-2) consists of the latebra, germinal disc, concentric
rings of yolk material and the vitelline membrane (a colorless membrane) that surrounds
and contains the yolk. The yolk constitutes approximately 31 percent of the total weight
of the egg.
b. The yolk grows by the gradual addition of the yolk fluid. Fat-soluble dyes are
transferred rapidly from the digestive tract to the bloodstream and then to the yolk.
Occasionally, what appears to be concentric layers of alternate dark- and light-colored
yolk fluid may be observed. However, modern feeding and production practices have
c. When the yolk is mature, the sac ruptures and allows the yolk to escape.
Each mature yolk is composed of a germ spot or germinal disc, a fatty substance known
as yolk, and the yolk membrane we call vitelline membrane and which surrounds the
d. The formation of an egg begins with ovulation, which is the release of the
matured yolk (ovum) from the ovary. Each developing yolk is enclosed in a sac
(vitelline membrane) in which blood vessels are distributed for the purpose of carrying
yolk-building substances to the developing yolk. One particular area of the yolk sac is
free of blood vessels and it is normally in this area, the stigma or suture line, that
ovulation or release of the mature yolk takes place (see figure 1-1). However, the
rupture of the yolk sac and release of the yolk sometimes occur at other than the stigma
with the result that one or more blood vessels are ruptured. This causes blood spots to
occur on the yolk or the white to become bloody.
e. Occasionally, reddish brown, brown, tan, or white spots commonly known as
"meat spots" may be found in the egg. These meat spots may be either blood spots
that have changed in color caused by chemical action or tissue sloughed off from the
reproductive organs of the hen.
FORMATION OF THE WHITE
a. The white (see figures 1-2 and 1-3) consists of several layers of albumen that
together constitute about 58 percent of the weight of the egg.
(1) The chalaziferous layer immediately surrounds the yolk and is
continuous with the chalazae (pronounced kay-lay-za). This is a very firm but very thin
layer of albumen. It makes up three percent of the total albumen.
(2) The inner, thin layer surrounds the chalaziferous layer and comprises
about 21 percent of the white.