What causes leg and foot diseases in chickens?

In the modern @#@230@#@ industry, the incidence of leg and foot diseases in chickens has increased, and they have become a problem that cannot be ignored in the chicken farming industry. At present, some chicken farms (households) lack sufficient awareness and understanding of leg and foot diseases in chickens, and often pay little attention to them, which easily leads to misdiagnosis and wrong treatment, causing unnecessary economic losses. Based on the author's many years of clinical practice and the clinical experience of many colleagues, the causes and similar symptoms of common leg and foot diseases in chickens in chicken production are summarized as follows.

1 Leg and foot diseases related to nutrition

1.1 Vitamin deficiency diseases

1.1.1 Vitamin B1 deficiency. Chicks often develop the disease suddenly. In the early stage, the feathers are rough, the feet are weak and powerless, and the bird sits on the ground leaning backward; then spasms of the legs, wings, and neck occur. Sick chickens rest on the hock joints and tail, with the head tilted backward, showing a "star-gazing" posture. Sometimes they fall to the ground and lie on their side, with the head tilted backward. Adult chickens develop the disease more slowly, with an unsteady gait and progressive paralysis.

1.1.2 Vitamin B2 deficiency. It occurs mostly in chicks from 14 to 30 days of age. The toes of sick chickens curve inward, especially the middle toe; the two legs cannot stand, and the bird rests on the hock joints. When it barely moves on its hock joints, it often spreads both wings to maintain body balance.

1.1.3 Vitamin D deficiency. Chicks are more prone to rickets, showing incomplete bone development, especially in the leg bones and ribs. Bone bending and weakness, fractures, and enlargement of the cartilage at the ends of the bones are common. In laying hens, the sternum becomes soft, the legs and wings are easily broken, and sometimes the legs are paralyzed, making the bird look penguin-like.

1.1.4 Vitamin E deficiency. Sick chicks have the head bent downward in contracture or twisted to one side, and some have the head tilted backward. The gait is unsteady, and the bird sometimes rushes forward or sideways, appearing "drunk." The two legs have paroxysmal spasms and cramps, with incomplete paralysis.

1.1.5 Choline deficiency. Growth is slow, the hock joints swell, the feet bend to the side, the tibial and toe joints become flat, the metatarsal bones are short, thick, and twisted, and fatty degeneration of the liver also occurs.

1.1.6 Biotin deficiency. Dermatitis occurs, with cracks and bleeding on the soles of the feet, and scabs around the corners of the mouth. Mild bone shortening and thickening sometimes occur.

1.1.7 Niacin deficiency. Bone shortening and thickening, swollen hock joints, arched feet, bent legs, and dermatitis occur.

1.2 Mineral and trace element imbalance

1.2.1 Ca and P deficiency and improper ratio. Chicks develop rickets, showing poor growth and development. The two legs are weak, the gait is unsteady, the leg bones become brittle and easily broken, the toes become soft and easily bent, the ribs are beaded, and the sternum is S-shaped.

1.2.2 Manganese deficiency. It causes perosis, characterized by swelling of the tibiotarsal joint, torsion or bending of the distal tibia and proximal metatarsus, and finally the gastrocnemius tendon slipping off from its ankle.

1.2.3 Selenium deficiency. It often occurs together with vitamin E deficiency. Sick chicks show general weakness, ruffled feathers, drooping wings, and paralyzed legs, and lie on the ground unable to stand.

1.2.4 Zinc deficiency. Growth is slow, the hock joints swell, and the skin is scaly.

1.3 High-protein feed. An excessively high protein content, especially an excessively high lysine content, can induce leg and foot diseases in chickens. Sick chickens stand still, have swollen and painful joints, move with difficulty and limp, and in severe cases become paralyzed.

2 Leg and foot diseases related to disease

2.1 Staphylococcosis, arthritis type. It is mostly seen in larger young chickens and adult chickens. Sick chickens squat, limp, lie on their side, or are paralyzed. The joints of the feet and wings become inflamed and swollen, especially the hock and toe joints, which are obviously enlarged. Toe tumors and swelling of the soles of the feet are sometimes seen.

2.2 Chronic pasteurellosis. The lesions are often limited to a certain part of the body, such as swelling of one or both wattles; nasal mucus discharge, swelling of the sinuses, and accumulation of secretions in the throat; arthritis with swollen and suppurative joints, lameness, and so on.

2.3 Infectious synovitis. The pathogen mainly attacks the synovial membranes of the tibial and metatarsal joints and the foot pads. In severe cases, it can spread to the synovial membranes of other joints, causing exudative synovitis, bursitis, and tenosynovitis. Sick chickens have difficulty walking and limp, with a gait like the character "eight" or like walking on stilts. The joints swell and become deformed, and large blisters appear on the chest.

2.4 Pseudomonas aeruginosa infection. Body temperature rises, movement is uncoordinated, there is trembling, and the bird lies on the ground unable to stand; the hock joints swell; the skin of the legs and abdomen of sick chicks is green; the claws have suppurative ulcers that form scabs, and green pus balls can be seen after the scabs are removed.

2.5 Aspergillosis. Chicks often show acute outbreaks, with a high incidence rate and a mortality rate of 1%-50%. In a few sick chickens, because the pathogen attacks the brain tissue, it causes neurological symptoms such as ataxia, opisthotonus, and paralysis of the legs and feet.

2.6 Chicken mites. They can sometimes cause skin inflammation with rough hyperplasia. After the inflammatory exudate dries, gray-white or gray-yellow scabs form, the feet swell, and the appearance is as if coated with lime, commonly known as "scaly leg." Over time, arthritis, toe bone necrosis, and difficulty walking can occur.

2.7 Newcastle disease. In cases with a long course, neurological symptoms sometimes appear, with uncoordinated movement of the whole body muscles (especially the leg and head muscles), the head and neck twisted to one side, or bent backward. Sometimes sick chickens have an unsteady gait, ataxia, move in circles, or walk backward; sometimes the wings are paralyzed, and the hind legs are paralyzed so that the bird cannot stand.

2.8 Marek's disease, neural type. Incomplete or complete paralysis often occurs, with the two legs one in front and one behind in a split posture, and the head and neck tilted or drooping. The sciatic nerve becomes yellow or gray, sometimes edematous, and locally or diffusely thickened.

2.9 Viral arthritis. It occurs mostly in broiler chickens and is characterized by arthritis, tenosynovitis, and rupture of the gastrocnemius muscle. In the early stage, sick chickens have a slightly abnormal gait, which gradually develops into lameness; they prefer to sit on the hock joints and move only when driven. The hock joints swell and cannot move, the affected limb cannot stretch, and the bird dares not bear weight. When the course is somewhat longer, a typical staggering gait appears, the affected limb is mostly twisted outward, and development is poor. 2.10 Avian encephalomyelitis. Sick chicks show an abnormal gait, bilateral ataxia, or incomplete paralysis. Sometimes the feathers are loose, and the head and neck show neurological trembling; when startled, they sway and move, squat, or even lie down. Sometimes they assume a dog-sitting posture and support the body with the hock joints and tibia while moving. As the disease progresses, the leg muscles become paralyzed, so that the bird cannot walk and is completely paralyzed.

2.11 Poisoning diseases. Poisoning by salt, urea, furazolidone, coal gas, sodium selenite, polyether anticoccidial drugs, and the like can also easily cause neurological leg and foot lesions, and sufficient attention should be paid to them. In addition, when chickens suffer from streptococcosis and infectious bursal disease, symptoms such as an unsteady gait, lameness, head trembling, or paralysis sometimes appear.

3 Leg and foot diseases related to environmental and genetic factors

They are often caused by wet and caked litter, excessive stocking density, low temperatures and cold in the early stage, stress factors that startle the flock, a rough and hard net bottom, and unreasonable spacing between slats, causing deformation of the toes and claws and damage to the foot pads in broiler chickens.

Skeletal deformation caused by genetic factors occurs mostly in purebred chickens and crossbred chickens, and may also be caused by congenital thyroid dysfunction.

In short, the causes of leg and foot diseases in chickens are extremely complex, and great attention should be paid to them and careful differentiation should be made. In particular, leg and foot diseases caused by infectious diseases can only be definitively diagnosed based on pathological necropsy changes and laboratory diagnosis.