Agriculture Reference
In-Depth Information
Nerve cells and muscle cells (after hatching) grow by cell enlargement. This same
process occurs in fat cells once birds reach puberty. Body fat acts as an energy reserve
and is the most variable of the body's components. Body fat varies greatly with breed,
sex, species, and age. It is strongly affected by nutrition.
Muscles are designed for producing movement by contraction. Since muscle is the
part of fowl that one is most concerned with when considering meat, it is the focus of
this discussion.
Muscles
There are three main types of muscle tissue: skeletal, cardiac, and smooth. Skeletal
muscles build up the body structure. Cardiac muscles make up the heart. Smooth
muscles are found in blood vessels and intestine. The function of muscle is primarily for
body movement, and in the process of movement, heat generation. Muscles also fill out
the shape of the body.
After puberty, most muscle growth is due to hypertrophy, which is why people who
raise their birds to make a nice tasty meal of fried chicken, roast goose, barbecued duck,
or roast turkey spend time making sure they are properly fed. The pectoral or breast
muscles are the largest in the bird and therefore garner the most attention as a food
source. This has become increasingly true with large-scale raisers. The modern broiler
chicken has huge breast muscles (see box on page 44 ) .
Other muscles of importance to meat raisers include the gastrocnemius muscle on
the back of the leg. This muscle is attached to the toes by the gastrocnemius tendon,
which, when relaxed, causes the toes to grasp a limb, thus allowing the bird to sleep on
a roost. It is also the muscle that makes up the tender, juicy “drumsticks.”
Two major types of skeletal muscle are also of importance: light and dark muscle.
Light muscle is so called because of low levels of myoglobin . Myoglobin is the oxygen-
holding molecule in the muscle. Muscles that are used more tend to accumulate more
myoglobin and thus are darker in color. The meat never gets very dark on modern broil-
er chickens because the birds get very little exercise and have very low levels of myo-
globin. An older breed or heritage-type chicken, turkey, duck, goose, pheasant, or quail
raised free range will have much darker “dark meat.” Certain breeds that are always on
the move will have extremely dark meat.
BONES GROAN ON RAPID GROWERS
Leg weakness — tibial dyschondroplasia — is a common problem with rapidly
growing strains of broiler chickens and commercial large-sized turkeys. It can arise
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