Skeletal Disorders

Skeletal Disorders are of two types.

A) Non Infectious Skeletal Disorders
B) Infectious Skeletal Disorders


A) Non Infectious 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.
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.
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 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.
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).

B) Infectious Skeletal Disorders

Coagulase-positive staphylococci (see alsostaphylococcosis,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.

Escherichiacoliis often responsible for flock outbreaks of arthritis and osteomyelitis in broiler chickens and turkeys. These outbreaks may be associated with respiratory disease.Pasteurellamultocidahas been isolated from arthritic joints in broiler breeders following use of live vaccines. Other sporadic causes of arthritis in poultry includeSalmonellaspp andStreptobacillusmoniliformis. Viral arthritis due to a reovirus has been reported as a significant cause of lameness in some parts of the world (seeviral arthritis,Viral Arthritis: Introduction). The virus is egg transmitted. Vaccines against the condition have been developed.
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.

Reference :- Merck Veterinary Manual

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