SHELL EGG INTRODUCTION AND INSPECTION EQUIPMENT
Section I. FORMATION OF THE EGG
a. The Defense Personnel Support Center purchased over 100 million dozen
shell eggs each year during the height of our participation in the Vietnam War. Who
was responsible to assure that the government received its dollar's worth of nutrition?
That responsibility was with the United States (US) Army Veterinary Service.
Shell eggs are probably the only item of subsistence on which you, the veterinary
food inspection specialist, must make a grade determination at destination. Shell eggs,
like anyother item of subsistence, cannot be graded until the factors that contribute to
the gradingsystem are known and understood. The terms used to describe an egg are
not necessarilyWebster, rather, they are the language of the trade, and you must know
those of and understand them so that you can properly grade eggs.
b. You must know about eggs, egg quality, and grading procedures. Such
knowledge of the "what" and "how" of the job, together with good judgment, practice,
and guidance from experienced supervisors, will enable you to acquire the necessary
skills to determine the proper classification of shell eggs according to official standards
of quality. To begin with, we will provide some background information on the
formation, structure, and composition of an egg so that you will be better able to
determine the classification of eggs.
The reproductive system of a hen consists of the ovary and the oviduct (see
a. Ovary. The right ovary is not functional. The left ovary, located directly
beneath the backbone opposite the last two ribs, secretes a hormone that aids in
balancing the body's glandular system, stores egg yolks, and regulates their release.
When a hen is hatched, the ovary contains its lifetime complement of yolk cells--3600
to 4000. Each mature yolk is composed of the germ spot (germinal disc), a fatty
substance known as yolk, and the yolk membrane, called the vitelline membrane.
When a hen reaches sexual maturity, the yolks begin to mature one at a time. During
this maturation process, a large amount of fatty substance is deposited in the sac
formed by the vitelline membrane (see figures 1-2 and 1-3). When the yolk is mature,
the sac ruptures and allows the yolk to escape. This rupture usually occurs along an
avascular zone known as the stigma, which has practically no blood vessels or nerves
(the remainder of the capsule has an abundant supply). The release of the yolk, called
ovulation, occurs again about 30 minutes after a finished egg has been laid. During the
laying "clutch" of a high-producing hen, ovulation can occur as often as every 22 hours.