Download Disorders of the Skeletal System Skeletal disorders cause lameness

Disorders of the Skeletal System
Skeletal disorders cause lameness from biomechanical
dysfunction and result in poor growth, culled birds, increased
mortality (caused by starvation and dehydration), and carcass
condemnation and downgrading. Production characteristics
of modern poultry lines (eg, body weight in broiler chickens,
egg production in laying hens) place high demands on the
skeletal system, and inadequacies in nutrition or husbandry
will often result in skeletal diseases. Skeletal disorders may
be primarily infectious or noninfectious; both may be seen
concurrently within a flock. Before postmortem examination,
flocks should be assessed; live, lame birds should be
examined, and an opinion as to general flock health, litter
quality, and management should be formed. Serum samples
may be collected for viral and mycoplasmal serology.
Noninfectious Skeletal Disorders
Rotational (Torsional) and Angular (Valgus/ Varus) Deformity :
These deformities often are seen as distinct flock problems.
Bones all exhibit some degree or combination of lateral,
medial, anterior, or posterior bend. They also show some
torsion (rotation) about their long axis. The most common
abnormalities are valgus deformity of the intertarsal joint and
excessive external rotation of the tibiotarsus. Valgus/varus
deformity is associated with rapid growth and little exercise.
The incidence can be reduced by slowing growth rate at an
early age by feed restriction or lighting programs. It may also
be due to chondrodystrophy due to B vitamin or trace mineral
deficiencies. Rotated tibia has been a major problem in
turkeys and a minor problem in Leghorns and guinea fowl.
The cause is poorly understood but has been associated with
early rickets. Poor mineralization of the bone, as in rickets,
increases the ease of deformation of the bone and therefore
the incidence and severity of deformities. Rickets may be
associated with nutritional deficiencies, enteric disease, or
malabsorption .
Spondylopathies :
Vertebral deformities and/or displacements (spondylopathies)
are common in thoracic vertabrae, particularly the fifth or free
thoracic vertabrae. Spondylolisthesis is the most common
deformity, but incidence is low in most flocks of broiler
chickens. It causes posterior paralysis due to spinal cord
compression .
Dyschondroplasia :
Dyschondroplastic lesions are masses of avascular cartilage
extending from the growth plate into the metaphysis and are
attributed to the failure of chondrocytes to differentiate. This
results in a focal thickening of the growth plate in the
proximal tibiotarsus (tibial dyschondroplasia) or sometimes
the proximal tarsometatarsus. The lesion in the proximal
tibiotarsus is often associated with anterior bowing of the
tibiotarsus and sometimes fractures below the plug of
cartilage. Factors shown to influence the incidence and
severity of dyschondroplasia include genetic selection,
calcium:phosphorus ratios in feed, metabolic acidosis
through excess chloride in feed, acid/base balance, and
mycotoxins. In a flock of modern broilers, the cause may be
marginal
inadequacies
in
dietary
calcium
or
a
calcium:phosphorus imbalance .
Rickets :
Rickets develops in growing birds due to deficiency of
calcium or phosphorus ( Calcium and Phosphorus
Imbalances) or insufficient vitamin D ( Vitamin D3 Deficiency).
Malabsorption can also cause a mineral deficiency. In rickets,
a failure of bone mineralization leads to flexibility of long
bones. Bone ashing and estimates of calcium and
phosphorus content combined with bone pathology are
useful diagnostic tools. Bacterial infections are common in
bones with rickets .
Plantar Pododermatitis :
Ulceration of the metatarsal and digital footpads is a common
cause of lameness in meat-type poultry. Wet or poor quality
litter is the common cause, although a biotin deficiency will
cause plantar pododermatitis even when litter quality is good.
Ulcerated footpads may become secondarily infected and
caked with litter .
Osteopenia (Osteoporosis and Osteomalacia :)
Osteopenia is a consequence of osteoporosis, a deficiency in
the quantity of fully mineralized, structural bone. Cage layer
fatigue describes a syndrome in which laying hens become
paralyzed in their cages. The bones of the birds are
osteopenic. The sternum is often deformed, and fractures
causes infolding of the ribs at the junctions of the sternal and
vertebral portions. Fractures can also occur in the long bones
and vertebrae. The medullary bone is osteomalacic. The
syndrome is due in part to a lack of exercise and high egg
production, but severe problems are associated with
inadequate calcium, phosphorus, or vitamin D. Calcium
requirements during growth and before and during lay vary
markedly. Sources of calcium that enable the slow release of
mineral, such as oyster shell, appear to give the best results .
Amyloidosis :
Extensive amyloid arthropathy is primarily caused by
Enterococcus faecalis , but not by all isolates. Clinical cases
are seen only occasionally and are most frequently seen in
the hock joint of a few replacement pullets or broiler breeders.
Cases may be attributed to the contamination of a previously
sterile vaccine diluent with E faecalis during administration
(eg, Marek’s vaccine in day-old chicks .
Infectious Skeletal Disorders
Control
Coagulase-positive staphylococci (see also staphylococcosis,
Staphylococcosis: Introduction) are frequently responsible
for bacterial infections in the bones and joints of broiler
chickens. Mycoplasma synoviae ( Mycoplasma synoviae
Infection ) may also play a role in infectious bone disorders
and can be monitored serologically.
In broilers, bacterial infections are most common in the
proximal femur and proximal tibiotarsus when the birds are
>22 days of age. In the proximal femur, the condition is also
referred to as femoral head necrosis. Recent reports indicate
this is the most common cause of lameness in broilers. The
etiology appears dependent on vertically transmitted
staphylococci in combination with a challenge by
immunosuppressive viruses (eg, infectious bursal disease,
Infectious Bursal Disease: Introduction). Floor eggs have
been shown to be common carriers of staphylococci, so their
use should be minimal. A high standard of hatchery hygiene
can reduce this risk. Formaldehyde fumigation within the
hatchers is also likely to help. In addition, hatchery fluff
samples can be examined to monitor for contamination with
staphylococci.
Staphylococcal infections in joints and tendons are also seen
in breeders. Outbreaks are likely to be due to management
practices or other diseases causing stress and/or joint and
tendon trauma (eg, competition over feed space, heavy
coccidiosis challenge). Insufficient lighting in the rear of
cages appears to predispose to an increase in bacterial
tenosynovitis.
Escherichia coli is often responsible for flock outbreaks of
arthritis and osteomyelitis in broiler chickens and turkeys.
These outbreaks may be associated with respiratory disease.
Pasteurella multocida has been isolated from arthritic joints in
broiler breeders following use of live vaccines. Other sporadic
causes of arthritis in poultry include Salmonella spp and
Streptobacillus moniliformis . Viral arthritis due to a reovirus
has been reported as a significant cause of lameness in some
parts of the world (see viral arthritis, Viral Arthritis:
Introduction). The virus is egg transmitted. Vaccines against
the condition have been developed.
Control:
Bacterial bone and joint infections often show a poor
response to antibiotic treatment. Antibiotics may be used to
control the bacteremia contributing to new cases and to
modify the bacterial flora within a flock. When individual birds
are of high value, injections of long-acting antibiotics may
improve some less severe cases. Control requires minimizing
sources of infection and stock susceptibility