Agriculture Reference
In-Depth Information
The skeleton of the bird is compact, lightweight, and very sturdy. The
vertebrae
(spinal column bones) of the neck are strong and flexible, but the mid-region (
thoracic
)
vertebrae and
lumbar
vertebrae in the lower back are fused to make a strong structural
support for flying birds. The
sternum
(breastbone) has the flight muscles attached to it
and protects the vital organs.
Proper skeletal development is crucial if muscle development is to occur.
Tibial dy-
schondroplasia
(leg weakness) is a periodic problem with rapidly growing strains of
broiler chickens, ducks, and large broad-breasted turkeys. The condition infrequently
arises in other breeds (see box,
page 46
). This leg weakness occurs when there is an
abnormally large number of
chondrocytes
(cartilage cells) and a dearth of
osteocytes
(bone cells) due to a surge in growth hormone. The bones grow without proper miner-
alization and
vascularization,
which is the development of fully functioning blood ves-
sels and structure, making them soft and incapable of supporting the animal's weight.
Modern broiler chickens and large broad-breasted turkeys have very soft bones.
Many times you can bite all the way through the bone, as it is extremely soft and pliable.
You could break a tooth, however, if you tried to bite through the leg bone of a tradition-
al or heritage chicken, turkey, duck, or goose butchered at sixteen weeks. These breeds
have completely different growth patterns and genetic makeup.
Female poultry have a specialized type of bone tissue called
medullary bone
, which
is used as a storage area for calcium for egg formation. Levels of parathyroid hormone,
calcitonin, vitamin D, and estrogen affect medullary bone. This bone is formed about
10 days prior to the formation of the first egg and accounts for about a 10 percent in-
crease in skeletal weight. This bone formation occurs only in laying hens, not in males
or immature females. Medullary bone is not a single bone, but a part of the bones found
in many parts of the body: the tibia, femur, pubic bone, sternum, ribs, ulna, toes, and
scapula. The marrow cavity of medullary bone is filled with fine interlacing needle-like
spicules
of bone to provide a ready supply of calcium for the shell of the egg.
FEATHERING FACT
Let's say you receive your first assortment of chicks in the mail and notice some are
beginning to get their feathers and others look funny and nearly bare. Should you be
concerned? Not at all. Genetics determine the rate at which a bird grows feathers.
Some birds feather slowly, some more rapidly.
Slow feathering is a
dominant trait,
meaning that it will express itself if present
in the genetic makeup of a bird, and is
sex-linked,
meaning the trait is carried on the
sex chromosomes. Fast feathering is desirable on broilers and laying hens. In rapidly
