- Review the patient’s clinical history and perform an external exam
- Thoroughly soak plumage in cold, soapy water or alcohol to promote cooling and reduce the risk of autolysis, while also minimizing airborne feather dander.
- Place the bird in dorsal recumbency and remove the ventral abdominal wall and sternal plate as one piece.
- After removing the keel, inspect the coelomic cavity.
- To expose the spleen, which is located dorsal to the proventriculus, grasp the ventriculus or gizzard and move the gastrointestinal tract to the right side of the bird.
- To begin the “pluck”, retract the tongue to expose the choana, then bluntly dissect along the esophagus until the crop is separated from the subcutis.
- Gently peel off the lungs from the underlying spine, by bluntly dissecting through fascia and reflecting the lungs from between the ribs with a scalpel handle.
- The kidneys appear as red-brown, lobulated structures that conform to a depression within the synsacrum.
- Remove the kidneys to expose the complete sciatic or lumbosacral plexus and the sciatic or ischiatic nerve.
The postmortem examination is a valuable part of the diagnostic work-up (Fig 1). When performing a necropsy, develop a routine and use a checklist.
Collect samples of everything. Place small or friable pieces in cassettes (Fig 2), or wrap tissue in gauze for protection and ease of later recovery. Photographs can also be useful.
Clinical Tip: When submitting a small patient for outside evaluation, submit the entire bird in formalin for best results. Open the body and skull to ensure adequate fixation of tissues.
When possible, verify the bird’s identity using a physical description, leg band, tattoo, and/or transponder chip. Identify gender in sexually sexually dimorphic species. Also note plumage and coloring. Is the bird molting? Are external parasites present? What is the general body condition? Are there any signs of trauma? Also be sure to examine the feet. Finally, consider survey radiographs, particularly when musculoskeletal disease or heavy metal toxicosis is suspected.
Sudsy water or alcohol
Thoroughly soaking plumage in cold, soapy water or alcohol serves a two-fold purpose (Fig 6). First, dry feathers serve to insulate the body, preventing adequate cooling (even when a body is placed in a refrigerator) and promoting autolysis. Soaking plumage in sudsy, cold water or alcohol helps to rapidly cool the carcass. After soaking plumage, the necropsy should be performed within 72-96 hours. Place the body in a freezer (or on dry ice) if it will take longer than 96 hours to perform the necropsy. If the carcass is frozen, do not thaw the tissues. Instead collect the appropriate samples and place in formalin without thawing to reduce freeze artifact.
Clinical Tip: Embryos, nestlings, and small adult birds are subject to particularly rapid autolysis.
Soaking plumage also prevents feathers from flying around and reduces the risk of airborne infection, like chlamydiosis. If psittacosis is suspected, soak the bird in a 5% quaternary ammonium disinfectant solution. A laminar flow hood should ideally be used.
Place the bird on its back. The ventral feathers can be plucked, if so desired.
Expose the sciatic nerve
Cut the loose skin overlying the sciatic or ischiatic nerve between the medial surface of the thigh and the abdomen (Fig 8). Reflect the leg laterally and expose the muscle overlying the sciatic nerve (Fig 9). The biceps femoralis sits caudal to the femur. Expose the femoral head and disarticulate the hip joint by pulling the leg pulled out and down to roll the head of the femur out of the acetabulum (Fig 10). Finally remove the musculature to expose the sciatic nerve (Fig 11).
Open the coelomic cavity
Open the coelomic cavity by making a transverse skin incision across the middle of the coelom, just distal to the sternum (Fig 12).
Remove the keel
Incise the left lateral side of the pectoral muscles (superficial and deep) and the costochondral junctions of the ribs (Fig 13). Then cut the right lateral side of the pectoral muscles and ribs (Fig 14). Examine the ribs and associated cartilages for thickening and beading characteristic of rickets in chicks. To remove the keel, disarticulate the shoulder joint or cut the rib bones, coracoid, and clavicle with bone shears or heavy scissors (Fig 15). Carefully inspect the air sacs as they are torn as the ventral abdominal wall and sternal plate are removed as one piece.
Inspect the coelomic cavity
After the keel is removed, inspect the coelomic cavity (Fig 16). Inspect the thyroid glands near the heart base (Fig 17). Examine the air sacs and viscera in situ, without touching them. Examine the surface of the liver for changes in color, size, shape, or consistency. A gallbladder is present in gallinaceous birds but is absent in most psittacine birds and pigeons.
Sample the air sacs and viscera as needed (Fig 18). Using sterile instruments, obtain cultures and impression smears. Always collect intestinal cultures last. A bile sample can also be collected.
Clinical Tip: Impressions of the lungs and spleen are useful when screening songbirds, like canaries and mynah birds, for atoxoplasmosis. Sarcocystosis can frequently be seen on impression smears of the lungs. Plasmodium, Hemoproteus, Toxoplasma, and Leucocytozoon are readily seen in impression smears of the liver and spleen.
Test yourself #1
Can you identify the structures shown above?
Video 1. Collecting an air sac sample for histopathology. Credit: Dr. Nobuko Wakamatsu-Utsuki.
Remove coelomic fat
Remove coelomic fat (Fig 19) and examine the pancreas. Free the left margin of the ventriculus or gizzard, then grasp the ventriculus and move the gastrointestinal tract to the right side of the bird to expose the spleen, which is located dorsal to the proventriculus. Examine the spleen for enlargement, hemorrhages, necrotic foci, and tumors (Fig 20).
Test yourself #2
Can you identify the structures shown above?
Video 2. Finding the avian spleen. Credit: Dr. Nobuko Wakamatsu-Utsuki.
Remove the skin on the neck to expose the trachea, esophagus, crop, and thymus (Fig 21). Examine the oropharynx, then cut along one lateral commissure of the mouth with scissors or an enterotome to expose the tongue, then take a closer look at the oropharynx (Fig 22). Retract the tongue to expose the choana (Fig 23), then bluntly dissect distally along the esophagus until the crop is separated from the subcutis (Fig 24).
Evaluate the entire respiratory tree. Make a longitudinal incision through the larynx, trachea, and syrinx, then bluntly dissect the fascial planes to carefully separate the lungs from the underlying spine (Fig 25, Fig 26). Reflect the lungs medially from between the ribs with a scalpel handle, then gently peel off the lungs (Fig 27, Fig 28).
Visit Waterfowl Anatomy & Physiology: A Dozen Key Facts for information on tracheal modifications in waterfowl.
Video 3. Removing a lung from the ribs. Credit: Dr. Nobuko Wakamatsu-Utsuki.
Test yourself #3
Can you identify the structures shown above?
The “pluck” is a term for the mass of organs removed outside of the body after the rectum has been transected (Fig 29, Fig 30). In the hen, also remove the ovary and oviduct and open the oviduct longitudinally.
Test yourself #4
Can you identify the structures shown here?
Evaluate the gastrointestinal tract, from the tip of the tongue to the cloaca. Make transverse sections through the tip of the tongue. Straighten the intestinal loops by cutting the mesentery. After an external exam of the intestines has been performed, open the gut by making a longitudinal incision with scissors. Begin with the esophagus, and continue down through the crop, proventriculus, ventriculus or gizzard, small intestine, ceca, colon, and into the cloaca (Fig 31-34). Large ceca are present in ground-dwelling birds that feed on plant material. They are most prominent in fowl and ostriches. Run the entire gut. Examine the mucosal surface and note the nature and odor of the contents. Also look for any lesions or parasites. Incise the ventriculus and proventriculus and evaluate musculature.
Visit these LafeberVet resources for additional information on the avian gastrointestinal tract:
- Anatomy and Physiology of the Avian Gastrointestinal Tract: Clinical Implications [RACE-approved webinar recording]
- Galliform Anatomy: A Dozen Key Facts
- Nutritional Strategy: Nectarivory in Birds 10 Facts You Should Know
- Passerine Anatomy: Ten Key Facts
- Pigeon Anatomy & Physiology
- Raptor Gastrointestinal Anatomy and Physiology
Bursa of Fabricius
The bursa of Fabricius is a dorsal median diverticulum of the proctodeum, or the caudal-most segment of the cloaca (Fig 35), which serves as the source of B-lymphocytes in the bird. In psittacine birds, the bursa is oval or pear-shaped with a central cavity (Fig 36).
Examine the heart for changes in size, shape, and color as well as major blood vessels and the pericardial sac.
Identify the adrenal glands, which are located cranial to the kidneys and dorsal to the oviduct (Fig 37).
The gonads are located near the cranial pole of the kidney, just caudal to the adrenal gland. These structures can change dramatically in size and color based on fluctuations in hormone levels. The testes are paired, bean-shaped organs (Fig 38). In the reproductively active hen, yolk-filled follicles may be observed (Fig 30).
The right ovary and oviduct usually regress so that only the left side develops in most adult birds (Fig 26). Although both ovaries are often present in a number of raptor species and within individuals of other orders, the right oviduct is less frequently retained in birds of prey.
Examine the ureters and kidneys in situ. The kidneys appear as red-brown, lobulated structures, which conform to a depression within the synsacrum. Avian kidneys consist of cranial and caudal poles OR cranial, middle, and caudal divisions (Fig 39).
Remove the kidneys to expose the complete sciatic or lumbosacral plexus and the sciatic or ischiatic nerve (Fig 40). Also note the glycogen body, which is a cleft filled with gelatinous material that sits within the dorsal midline of the lumbosacral enlargement. This structure is unique to birds and its function remains unknown.
Video 4. Exposing the sciatic or ischiatic nerve. Credit: Dr. Nobuko Wakamatsu-Utsuki.
Bones and joints
Evaluate the legs and wings, as well as joints, bone marrow, and growth plates. Break a leg, noting bone strength. Incise the femorotibial and tibiotarsal joints. Check joints for growth abnormalities and/or inflammation. Use an osteotome, split one femur longitudinally and examine the bone marrow. Also incise the foot pads to look for pododermatitis lesions.
The brachial plexus is best seen anterior to the first rib (Fig 25). Examine the brachial plexus in conjunction with the intercostal nerves for signs consistent with leukosis in fowl. The right and left nerve trunks should appear as mirror images.
The infraorbital sinus is an extension of the cervicocephalic air sac system present in several orders of birds, including psittacines. The infraorbital sinus is found subcutaneously lateral to the nasal area and rostroventral to the eyes. The sinus can communicate with pneumatized portions of the skull as well as the upper beak, mandible, and/or orbit. Insert one blade of sterile scissors into the sinus space, then make a longitudinal lateral incision through the wall of each sinus and examine these spaces. Collect a sterile culture of the sinuses, when indicated.
To access the sinuses, remove the upper beak with a transverse cut near the eyes using heavy scissors or tin snips. This will allow the nasal cavity to be inspected and will expose the open anterior end of the infraorbital sinus.
The avian globe is very large in relation to bird body size. There are three basic globe shapes: flat, globoid, and tubular. Flat globes are typical of many birds. Globoid eyes are typical of diurnal birds. Tubular globes are seen in owls (Fig 41). The shape of the eye is maintained by 10 to 18 scleral ossicles.
Disarticulate the head from the atlanto-occipital joint and remove the skin overlying the skull (Fig 42). Then carefully remove the calvarium with strong scissors or rongeurs to expose the brain (Fig 43, Fig 44). It is often helpful to tilt the head or even hold the skull upside down. Cut the cranial nerves as needed and handle the brain tissue as little as possible.
Handling of necropsy samples
|Table 1. Appropriate handling of necropsy samples for various tests|
|Toxicological testing||Freeze at -20°C in aluminum foil|
|Viral isolation||Freeze at -70°C|
|Formalin fixation||10% formalin penetrates approximately 2 mm in 24 hours.
Therefore a sample size of 1.5-2 mm is preferred (no pieces thicker than 0.5 cm).
Provide a 10:1 ratio of formalin to tissue.
|Gout suspected||100% ethyl alcohol|
Description of necropsy lesions
|Table 2. Description of lesions identified at necropsy|
|Size or volume||Measurements, 3 dimensions, ml, % of parenchymal involvement|
|Shape||Cordate, reniform, sinuate, serpiginous, endophytic, exophytic, lobed, papillary|
|Distribution||Diffuse, disseminated, focal, patchy, irregular, scattered|
|Cut surface appearance||Solid, cystic, uniform, varied|
References and recommended reading
Abdul-Aziz T, Barnes HJ. Gross Pathology of Avian Diseases: Text and Atlas. Jacksonville: American Association of Avian Pathologists; 2018.
Altman RB, Clubb SL, Dorrestein GM, Quesenberry K (eds). Avian Medicine and Surgery. WB Saunders; Philadelphia, PA. 1997.
Boulianne M (ed). Avian Disease Manual, 7th ed. Jacksonville: American Association of Avian Pathologists; 2013.
Reavill D. Avian necropsy procedures and common findings. MASAAV Issue 2 1998:2-7.
Wakamatsu-Utsuki N, Pollock C. A guide to avian necropsy. LafeberVet Web site. August 25, 2019. Available at https://lafeber.com/vet/a-guide-to-avian-necropsy/