Etiological Analysis and Diagnostic Identification Methods for Leg Disorders in Chickens

During the rearing process, chickens frequently develop leg disorders such as soft legs, lameness, paralysis, squatting reluctance to move, leg and claw deformities, and paralysis. The causes of leg disorders in chickens are extremely complex. Most leg diseases are a symptom of some disease, or a type within some disease, and very few are independent diseases, which some people call weak leg syndrome. The occurrence of leg diseases in a flock directly affects flock uniformity, increasing the culling rate and sporadic mortality rate of the flock. This article provides the following overview of the causes and characteristic identification of leg disorders in chickens.

Etiological Analysis of Leg Disorders in Chickens

1. Viruses

(1) Newcastle disease

This disease manifests in multiple types. In the subacute or chronic form, affected chickens may show paralysis of the legs and wings, lameness, unsteady standing, head tilted backward or twisted to one side, some with unilateral leg paralysis resting on the metatarsus, and some with paralysis of both legs; when startled, the whole body convulses and the body rolls over.

(2) Avian encephalomyelitis

This disease, also known as epidemic tremor, mainly occurs in chicks aged 5 to 25 days and is transmitted both vertically and horizontally. Initially, affected chickens show trembling of the head and neck, then gradually develop ataxia, and finally become paralyzed, lying down unable to rise with both legs stretched to one side, until death.

(3) Marek's disease

It mostly occurs after 70-80 days of age. The neural form of Marek's disease can affect the sciatic nerve, manifesting as locomotor ataxia, with unilateral or bilateral paralysis, one limb forward and the other backward, in a "splits" posture.

(4) Viral arthritis (viral tenosynovitis)

Caused by avian reovirus, this disease is common in broilers at 2 weeks of age, with obvious symptoms appearing at 3 to 4 weeks of age, such as reluctance to move, lameness, joint swelling, bending and deformity of the foot joints, and rupture of the gastrocnemius tendon.

2. Bacteria

(1) Infectious synovitis of chickens (mycoplasmosis)

With Mycoplasma infection, affected chickens show pale combs, cessation of growth, swelling of joints (especially the hock and toe joints), lameness, a tendency to squat, swelling of the hock joint or foot pad, and viscous, grayish-yellow exudate in the synovial bursa.

(2) Avian tuberculosis

Affected chickens are depressed and show obvious weight loss. When the bones are invaded by the pathogen, they show unilateral lameness, walking with a special hopping gait; tuberculosis within the joints can cause paralysis.

(3) Inclusion body hepatitis

The chicken's feathers are ruffled, the comb is pale, and there is anemia; the liver is yellow and friable with hemorrhagic points and necrotic points; the bone marrow of the femur is pale pink or yellow; extensive hemorrhage occurs in the pectoral muscles, leg muscles, subcutaneous tissue, and visceral tissues.

(4) Bacterial arthritis

It is characterized by inflammatory reactions such as redness, swelling, heat, and pain in the legs and joints, causing affected chickens to limp and squat unwilling to move. The causes of this disease include Staphylococcus infection, Campylobacter hepatitis, Escherichia coli infection, Salmonella infection, streptococcosis, and fowl cholera, among others.

(5) Avian paracolon bacillosis

The pathogen is Paracolobactrum. Affected chickens develop diarrhea, leg paralysis, neck torsion, sitting on the hocks, ataxia, body tremors, and pass yellow-white feces that sometimes contain blood.

(6) Transient paralysis disease

According to Bi Yingzuo (Poultry Research Laboratory, South China Agricultural University, 1994), the cause of this disease is still unclear. It often occurs in chickens at 6-8 weeks of age; affected chickens develop flaccid paralysis of the neck and wings and complete paralysis of the legs, and most can recover after 1 to 3 days. After the restricted feeding period ends, chickens may also develop a transient paralysis due to overeating pressing on the vagus nerve.

(7) Avian spirochetosis

The pathogen is a spirochete. Affected chickens show reduced appetite, listlessness, ruffled feathers, lethargy, cyanosis of the head, diarrhea, thirst, unsteady staggering gait, and finally become paralyzed, dying from extreme weakness.

3. Parasitic

(1) Leucocytozoonosis (Caure's leukocytozoon disease)

This disease occurs only in chickens, with the highest incidence at 1 to 3 days of age. The main manifestations are depression, ruffled feathers, anemia, pale comb, yellow-green loose feces, difficulty walking, ataxia, mild paralysis of both limbs, and stunted growth.

(2) Knemidokoptes infestation in chickens

Knemidokoptes usually parasitizes the feathered areas of the chicken's shank and feet. The mites can burrow into the skin, with tunnels beneath the scales of the lower leg. Their parasitism causes inflammation, with scaly debris on the shanks, followed by skin hyperplasia and roughening, itching cracks, and the exudate from the affected area drying to form gray-white scabs, presenting as "gray leg," leading to difficulty in movement and even progressing to arthritis and toe bone necrosis.

4. Trauma

Inflammation caused by mechanical fractures and sprains.

5. Nutritional and metabolic diseases

(1) Gout

It is caused by excessive intake of animal protein by chickens, resulting in obstructed excretion of urate, a protein metabolic product. Any factor causing renal dysfunction can cause this disease, such as VA deficiency, water deprivation, and high-calcium diets. Articular gout can be seen in the cartilage of joints (toe joints), periarticular tissues, tendon sheaths, and ligaments, with urate accumulating into nodules, causing swelling and thickening of the joints or between the toes.

(2) Imbalance of Ca and P ratio

When the Ca and P ratio in chicken feed is improper for a long time, growing chickens show weakness of both legs, unsteady walking, and lameness; in severe cases, they lie on their sides unable to rise, with the legs splayed in a "V" shape. Adult chickens show reduced egg production and lay soft-shelled eggs. On necropsy, the femur is easily broken and can be crushed, the femur is soft and easily bent, the epiphyseal growth plate is widened, the beak becomes soft like rubber, the keel is "S"-shaped, and the junctions of the ribs and spine show bead-like swellings.

6. Vitamin deficiency

(1) VB1 deficiency

It causes polyneuritis and peripheral nerve paralysis in chickens. Affected chickens are anorexic, have weak and soft legs, unsteady gait, and toes curled inward. At first, affected chickens raise their heads and lift their feet high when walking; as the disease progresses, they move on the hock joints, with the body bent over the legs; in severe cases, both limbs are paralyzed, lying unable to rise, with both legs extended and the head tilted backward in a "stargazing" posture.

(2) VB2 deficiency

Affected chickens walk on one foot or on the hock joints, with swollen joints, toes curled inward, or one leg forward and one leg backward, difficulty walking, and when walking they spread both limbs to maintain body balance. On necropsy, the sciatic nerve is seen to be swollen.

(3) VE deficiency

Difficulty walking, paralysis of both legs, falling to lie on the side, legs extended outward, unilateral opisthotonus, spasms and convulsions of both legs, and death soon after.

(4) Choline deficiency

It can cause perosis, with enlargement of the hock joint, and the foot bending to the side, producing slipped tendon disease.

(5) Niacin deficiency

When chicks are deficient in niacin, the leg joints become swollen and the toes and claws appear spasmodic. When growing chickens are deficient in niacin, growth stagnates, joints swell, bones become short and thick, legs bend, and walking is difficult.

(6) Nicotinic acid deficiency

Swelling of the hock joint and difficulty walking.

(7) Biotin deficiency

It can cause slipped tendon disease, with cracking, bleeding, and scabbing of the skin of the soles and toes, and pododermatitis of the foot pad, which is a typical symptom of biotin deficiency.

(8) VA deficiency

Swelling of the leg joints, with white urate in the joint capsule, and difficulty walking.

(9) Folic acid deficiency

Affected chickens show poor growth, abnormal feather development, anemia and perosis, and abnormal walking.

(10) VD3 deficiency

Extreme weakness of the legs, difficulty walking, a special posture of sitting on the legs (squatting posture), and later the beak, claws, and keel become soft and easily bent.

7. Mineral deficiency

(1) Zn deficiency

Affected chickens show weakness of both legs, ataxia, short and thick long bones, swelling of the hock joint, scaly skin on the legs and feet, and in severe cases necrotic dermatitis.

(2) Manganese deficiency

When poultry is deficient in manganese, it causes enlargement of the tibial joint, torsion or bending of the distal tibia and proximal phalanges, and finally slipping from the gastrocnemius tendon, making walking difficult.