Lameness disorders in poultry
Emily Martin
Animal Health Laboratory, University of Guelph, Guelph, ON
AHL Newsletter 2021;25(2):22.
Lameness in poultry can develop due to abnormalities in the skeletal, muscular, nervous or vascular systems. There can be subtle differences in the definitions, therefore, careful attention to detail is needed to determine the cause. The following are short descriptions of lameness disorders in poultry.
Developmental:
Angular bone deformity (valgus, varus): This is a long bone deformity. There is angulation of the distal tibiotarsal bone, deviation of the lower leg, and often bending of the proximal shaft of the tarsometatarsal bone. The tendon may be displaced. The legs curve together (valgus, feet lateral) or bow out (varus, feet medial).
Tibial rotation (twisted leg): Also a long bone deformity where the tibiotarsal bone is rotated through the long axis causing the leg to often extend laterally. The tendon is not displaced. This deformity is usually unilateral, can approach 90 degrees, and the cause is unknown.
Tibial dyschondroplasia (TD): Retained cartilage across part or entire width of the growth plate. Dyschondroplasia can occur in bones other than the tibia. Multiple contributing factors include: growth rate, Ca/P ratio in the diet, and electrolyte imbalance.
Spondylolisthesis (kinky back): Due to conformation and growth rate, the 4th thoracic vertebra is displaced, pinching the spinal cord resulting in posterior paresis and paralysis. Birds sit on hocks with feet slightly raised off the ground.
Splay legs: Occurs in birds less than 2 weeks of age. The legs twist laterally during development due to slippery surfaces. One or both legs are affected.
Slipped tendon (perosis): The gastrocnemius tendon is subluxated (slipped) due to hock deformation. The leg is malpositioned distal to the hock (usually laterally). Caused by nutrient deficiencies affecting growth plate development.
Dietary:
Rickets: Rapidly growing birds are susceptible to deficiencies or imbalances in Vitamin D, Ca or P. Malabsorption syndrome can also cause rickets. Birds are lame or, in subclinical situations, the flock can have poor performance, poor gait, and increased bone deformities.
Osteoporosis/Cage layer fatigue: Occurs in laying hens due to decreased mineralization of structural bone causing bones to be fragile and prone to fracture. Caused by high production (bone loss for egg shell formation), vitamin D/Ca/P deficiencies, age, housing, etc. Birds can be found paralyzed, alert and lying on their side. They can also be found dead with a shelled egg in the shell gland. The bones are fragile, brittle and may be fractured. The sternum may be deformed and the ribs infolded.
Infectious: Bacterial
Arthritis/Tenosynovitis: These conditions can develop after trauma, prolonged recumbency or secondary to a systemic infection. Acute lesions include redness, pain, heat and swelling. Joint exudate is opaque yellow, and yellow caseous deposits can develop within the joint. Chronic arthritis can lead to degeneration of articular cartilage, potentially affecting the underlying bone causing osteitis. Bacteria most often isolated include: Staphylococcus aureus, Enterococcus cecorum, and E. coli.
Bacterial chondronecrosis with osteomyelitis (BCO): Rapid growth results in excessive stress on growth plates of the proximal femur, proximal tibiotarsus, and the flexible thoracic vertebrae. This creates (osteochondrotic) clefts among the chondrocytes of growth plates. Circulating opportunistic bacteria colonize these clefts resulting in necrosis and granuloma formation within the growth plates at these 3 sites.
Septic osteomyelitis: This condition is similar to BCO and occurs in the same anatomic locations. It is secondary to bacteremia where circulating opportunistic bacteria settle out in the tight vasculature of the growth plates and also create areas of necrosis and granuloma formation. For both BCO and septic osteomyelitis, common bacteria isolates include: Staphylococcus aureus, Enterococcus cecorum, and E. coli.
Pododermatitis (Bumblefoot): These footpad lesions are due to trauma or poor litter condition and can lead to lameness. Secondary musculoskeletal lesions can include arthritis, osteomyelitis, and/or tenosynovitis. The AAAP has a footpad scoring guide available at this site: https://aaap.memberclicks.net/assets/documents/store/broiler%20paw%20scoring%20guide%20aaap%202015%20final.pdf
Infectious: Viral
Reovirus (viral arthritis): Reovirus infection can cause viral tenosynovitis primarily of the hock joint, and can sometimes result in rupture of the gastrocnemius tendon. Reovirus can also be involved in a malabsorption syndrome that could cause secondary osteodystrophies such as rickets and twisted legs.
Marek’s Disease: This is a herpesvirus that can cause paralysis, lymphoid tumours and immunosuppression. It is ubiquitous in the environment and highly contagious. Infected birds develop a latent infection and continuously shed the virus. The virus causes inflammation in peripheral nerves such as the sciatic that can result in incoordination, progressive lameness or paralysis. A characteristic presentation is a bird with one leg stretched forward and the other back.
Infectious: Mycoplasma
Synovitis: Mycoplasma synoviae and Mycoplasma meleagridis cause infectious synovitis as well as respiratory disease. The joint exudate is translucent and gelatinous unlike the opaque exudate of bacterial infections.
Toxicity:
Ionophore toxicity: Severe myodegeneration of the adductor leg muscle results in reluctance to move and lameness. This is usually caused by feed mixing errors related to ionophore coccidiostats.
Other:
Femoral Head Necrosis (FHN): This condition is a postmortem description with multiple potential causes including: bacterial osteomyelitis, iatrogenic trauma, osteoporosis and rickets.
Spontaneous bone fracture: Fractures can be caused by rough handling, especially when catching for slaughter.
Please refer to the companion article published in the AHL March 2021 newsletter explaining how to examine and sample cases of lameness with accompanying photographs. AHL
References
1. Casaubon Huguenin MT, Brugère-Picoux J. Diseases of the Musculoskeletal System. In: Manual of Poultry Diseases. Brugère-Picoux J et al, eds. AFAS, 2015:448-459.
2. Shivaprasad, HL. Musculoskeletal Disorders. In: Avian Disease Manual, 7th ed. Boulianne M, ed. AAAP, 2013:209-211.
3. McNamee PT, Smyth JA. Bacterial chondronecrosis with osteomyelitis ('femoral head necrosis') of broiler chickens: A review. Avian Path 2000;29(4):253-270.
4. Wideman, R. Bacterial chondronecrosis with osteomyelitis and lameness in broilers: A review. Poultry Science 2016;95(2):325-344.