Poultry lameness: Examination and sample collection
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2021;25(1):13.
Veterinarians who treat commercial or backyard flocks will inevitably encounter lameness issues. The source of the lameness can exist anywhere from the spine to the foot, therefore, postmortem examination must include a thorough examination of the entire neuro-musculo-skeletal system. It is also important to submit appropriate samples to the lab for follow-up testing. The following is a description of the postmortem examination process and photographs of potential samples to collect.
Examination should start at the foot and work up towards the spine.
1) Foot – Should be examined for dermatitis. The American Association of Avian Pathologists (AAAP) has a reference document for footpad scoring that you can access here:
2) Hock – Examine the skin behind the hock for swelling or discolouration around the gastrocnemius tendon. Pluck the feathers around the joint to ensure the feathers will not contaminate any sampling attempts. Cut the hock open from the front, being careful not to contaminate internal tissues or fluid (Fig.1). Swab using gel swabs for bacterial culture or viral transport media (VTM) swabs for PCR testing (Fig. 2).
3) Tendon (Gastrocnemius) – Once the hock joint is opened and swabbing is complete, continue cutting up the sides of the tendon behind the hock. Continue opening until you can access the gastrocnemius tendon to make a high transverse cut (Figs. 3,4). You can then make another transverse cut nearer to the joint to collect a short length of tendon to submit for histology (Fig. 5). On histology, a cross section through this tendon allows the pathologist to evaluate multiple tendons. In commercial turkeys where turkey arthritis reovirus (TARV) is suspected, it is important to also collect the group of tendons running along the back of the shank for histopathology (Fig. 6). Including the skin keeps the tendons attached for ease of trimming.
4) Stifle (Knee) – This can be a challenging joint to open. If the bird(s) are well fleshed there will be a line of fat running at a downward angle toward the body. Cutting along this line of fat will open this joint (Fig. 7). Look for increased amount of discoloured fluid.
5) Tibiotarsal bone (proximal) – In younger birds, the growth plates should be examined for abnormal development (rickets, tibial dyschondroplasia (TD)) or localization of bacteria (osteomyelitis). For histology, it is important to consistently collect the same sample for identification of TD lesions, and to provide comparable samples among birds for examination. Along the medial surface of the proximal tibiotarsal bone, slice the medial surface of the bone to reveal the growth plate without cutting the growth plate or articular cartilage off (Fig. 8). If abnormalities are suspected, collect the proximal end of the tibiotarsal bone, trim most of the musculature off, and place into formalin (Fig. 9).
6) Skeletal muscle and sciatic nerve – If Marek’s disease is on your list of rule-outs, you will need to submit sciatic nerve for histologic evaluation. Along the medial aspect of the leg, there is a triangular muscle (pubo-ischio femoralis) that is a key muscle to collect and submit if you are suspecting ionophore toxicity (Fig. 10). This is also the muscle to reflect to locate the sciatic nerve (Fig. 11).
7) Femoral head – When the leg is initially reflected, the leg can be forced laterally to pop the femoral head out of the acetabulum (so the bird will lie flat) (Fig. 12). If the femur fractures adjacent to this joint (neck of the femur), this is called femoral head necrosis (or bacterial chondronecrosis with osteomyelitis) and can indicate the bone is weakened from a bacterial infection. The bone marrow can be swabbed (gel swab) at this point to submit for bacterial culture. Examine the femoral head and acetabulum for any abnormalities.
8) Spine – The final location to examine is the spinal column. There is one movable joint in the spine of poultry and it is located in the region of the caudal lungs/cranial kidneys. Depending on the size of the bird, take either a scalpel or knife and split the spine right down the middle (Fig. 13). Pry the spine open and look for irregularities in the formation of the spine (kinky back) or abscess formation in the vertebrae (swab for bacterial culture) (Fig. 14).
|Figure 1. Opened hock||Figure 2. Hock swab (gel)|
|Figure 3. Gastrocnemius tendon||Figure 4. Transverse section|
|Figure 5. Submit piece of tendon||Figure 6. Shank tendons.|
|Figure 7. Stifle||Figures 8. Growth plate, remove entire proximal tibiotarsal bone and formalin fix.|
|Figures 9. Growth plate, remove entire proximal tibiotarsal bone and formalin fix.||Figure 10. Reflect muscle (white star) to collect sciatic nerve.|
|Figures 11. Reflect muscle (white star) to collect sciatic nerve.||Figure 12. Exposed femoral head.|
Figure 13. Split spine.
|Figure 14. Examine spine for abscesses|
Additional sampling notes: The sciatic nerve also runs through the kidney. If there are any kidney lesions, it could be impinging on the nerve and causing lameness. AHL