Necropsy examination of the fowl present special problems. First, diseased or dead birds submitted for necropsy examination most often come from a large flock. Thus, there are no guarantees that the bird sample submitted represent the true picture of the health status of the flock. Isolated cases of diseases are therefore possible, and information gained following necropsy may thus be difficult to interpret for the rest of the flock. The basic question that must be answered is whether necropsy examination will shed light on the disease process affecting a significant proportion of the flock. Therefore, for necropsy examination to be meaningful, careful sampling of the flock is essential, and that samples submitted for necropsy should be those representing a wide spectrum of clinical signs observed on the flock. It is best to submit birds that are showing the earliest signs of the disease in question, at its worse state, and include also those dead birds that succumbed from the disease in question.

Second, avian species tend to have a limited repertoire of signs following disease, such that critical history taking is essential. Moreover, it is generally recognised that most avian diseases are multi-factorial in aetiology. Information on the type of housing, ventilation, diet, husbandry practices, sources of stocks, number of birds affected, the stage of production, and the rapidity by which the disease spread of in terms of days elapsed following the appearance of the clinical signs should be obtained to properly evaluation the situation.

Third, diagnosis of most avian diseases requires ancillary laboratory tests apart from necropsy. In most cases, there are no substantial gross changes that may be considered diagnostic, although clues may be derived from these gross changes on the best laboratory test that must be employed.

Fourth, it must be remembered that species difference exists, and that the examiner should be aware of these differences between and within species of birds. Many veterinarians are caught off guard whenever species other than domestic chicken is presented for necropsy.

Fifth, the fact that birds has feathers lend themselves not amenable to physical examination, the feathers causing much difficulty for the examiner. Consider the number of birds submitted for necropsy for a given disease in question, this may require a considerable amount of time. Yet, physical examination is an essential prelude to necropsy.

The proceeding discussions of the techniques for avian necropsy will use the domestic chicken as the model. The same technique may be easily adapted to the necropsy examination of most avian species.
 

PHYSICAL EXAMINATION
 

Birds submitted alive for necropsy should first be examined prior to euthanasia. A systematic approach in the physical examination of the samples should be done. Ruffling of the feathers to view the skin from the head and proceeding caudally is best.

For live birds, take particular attention to the body conformation and the behavior of the birds bearing in mind what is supposed to be normal for the species, breed and age. Allow the birds to rest for a while if they were transported. If blood samples may be required, it should be taken at this stage.

Take note of any swelling on the infraorbital sinuses, discharges on the nostrils, beak deformation, feathering, distention of the crop, the appearance of the foot pads and cloacal discharges. With the aid of a magnifying glass, ruffle the feathers under the wings and around the cloaca and examine for the presence of ectoparasites. The skin should be examined for the presence of lumps, bruises, wounds and other abnormalities.
 In interpreting cloacal discharges, it must be remembered that the cloaca or vent is the common opening for both the alimentary and uro-genital system. Soiling of the feathers around the vent need not indicate gastrointestinal pathology. The discharges should be qualified as to nature, colour, consistency and odor.

 EUTHANASIA

Most avian species can be humanely killed by atlanto-occipital disarticulation. This technique however requires practice and care must be taken not to break the skin or totally obliterate the head from the neck makes a lot of mess. To do this, hold both legs and the wings with one hand. Grasp the head and neck with other hand. Secure the head between the thumb and the pointing finger. Position the thumb at the base of the neck and the pointing finger at the base of the lower beak. Hold the bird firmly and with a sudden jerk, twist the hand holding the head to disarticulate the neck.

Figure 15. Cervical disarticulation in domestic fowl. Note the positioning of the thumb
and the rest of the fingers. Inset: Direction of pull.

Large birds may react violently to the procedure such that adequate restraint is essential. Alternatively, chemical means of euthanasia may be done. For large birds, intraperitoneal or intravenous administration of barbiturates may be used. Small birds may be euthanased using inhalant agents such as chloroform or ether. Soak a piece of cotton in any of these agents and put it on a container with a lid. Place the bird on the container and close the lid.

 OPENING THE BODY CAVITIES

Minimal equipment is often required in fowl necropsy and these include a pair of scissors, forceps, bone cutter and a knife. Prior to opening the bird, it is best to wet thoroughly the whole bird in a detergent solution. This will lessen the chances of feathers floating around the area while the examination progresses. Lay the bird on a pad of newspaper on the table. The paper serves to absorb most blood and fluid, and provide a convenient wrapper for the carcass after examination. Position the bird so that the legs and feet are facing the examiner.
 

Figure 16. Skinning the bird. The skin is manually dissected from the abdomen to the neck
region. Note the line of incision to open the abdominal cavity

For your birds, break the skin in between the thighs towards the back, disarticulating the hip joint on the process. This will enable the specimen to be laid down flat on the table. The skin at this portion of the body may be easily broken in most domestic fowl. In old and large birds however, this may not be easily done and incisions through the skin and adductor muscle using a knife may be required. Grasp and cut the portion of the skin still covering the abdomen and pull the skin towards the neck region exposing the abdomen and breast on the process. At this point, note the amount of flesh in the breast and thighs of the bird, and any discoloration on the subcutaneous tissues. Dissect the skin covering the crop and the neck.
 

Figure 17. Schematic diagram of the relative location of the air sacs in domestic fowl.
Ce- cervical; Cl- clavicular; Ax- axillary; At- anterior thoracic; Pt- posterior thoracic; Ab- abdominal air sacs.

With the aid of a pair of forceps, lift gently the muscle at mid-abdomen and cut through it horizontally using a pair of scissors. While doing this, examine the paired abdominal airsac. Note the opacity of the sac and its contents if any. Continue the cut until it reaches both side of the abdomen and upward towards the last set of ribs. Lift the breast and cut the set of ribs at both sides. While doing this, examine the paired anterior and posterior thoracic air sacs. Free the breast from attachments of the liver and heart. Using bone cutter or a large heavy-duty scissors cut the pectoral muscle and clavicle at both sides to free the breast. Care must be exercised not to unnecessarily severe the trachea, syrinx, brachial vessels, or cut open the crop. Remove the freed breast.

Next, position the bird so that the feet are facing the left side of the examiner and the head of the bird facing the examiner's left side. Open the mouth and insert the point of the scissors at the commissure of the beak. Cut the commissure of the beak and continue the cut towards the throat. Locate the opening of the oesophagus and cut through towards the crop. Examine the contents of the crop and the appearance of the mucosa. Do the same for the trachea and cut through towards the syrinx. While doing this, examine the thymii, thyroids and parathyroids which are located at the lower neck region and at the thoracic inlet. Reposition the bird so that the feet are facing the examiner.

 DISPLAY STAGE

Examine the organs in situ after completing the preliminary cuts to expose the visceral organs. As in mammalian necropsy, the arrangements of the organs, presence of fluids in body cavities, and evaluation of the appearance of most organs are done at the display stage. Also, samples for laboratory examination may be obtained at this stage. The relative size of the organs can be gauged at this stage, but the normal conformation for the species, breed and age should be known. Since most students of necropsy encounter difficulties identifying some structures in avian species, a short review follows.

In birds, there is no structure homologous to the mammalian diaphragm. Thus, there is no distinct separation between thoracic and abdominal cavity except for two thin membranes, the pulmonary aponeurosis and oblique septum. The lungs are small and are attached to the ribs. The liver is usually large and bi-lobed. A gall bladder may be present in some species (e.g., chicken, duck and goose) or may be absent (e.g., pigeons). The gizzard is usually reflected to the right side of the specimen. An ovoid spleen is positioned near the proventriculus. Segments of the intestines, caecum, and colon can be observed in the intestinal mass reflected with the gizzard. The duodenum forms a loop that accommodates the pancreas. From the duodenum, there is no clear demarcation into jejunum and ileum. A paired caeca is present, and a short large intestine is not clearly delineated into colon and rectum. This enters into the formation of the cloaca. The kidneys are lobulate and closely attached to the sub-lumbar region. The ureters open into the cloaca. A urinary bladder is absent in avian species. Located close to the cloaca is the bursa of Fabricius. A left ovary and oviduct are always found at the left side, the right structures being undeveloped. There are no lymph nodes in birds. The long bones usually contain air spaces with minimal amount of marrow at the extremities.

EXAMINATION STAGE

The visceral organs in avian species may be examined in situ. If required, the liver, spleen, gizzard, proventriculus, and the whole intestinal tract may be detached to facilitate the examination of other organs. Grasp the proventriculus and cut the oesophagus. Lift the gizzard, the proventriculus, liver and the whole intestinal tract and severe their attachments. Cut the large intestine a short distance from the cloacal opening. Lay the severed organs at the table.

Examine the liver and spleen. Open the proventriculus and gizzard longitudinally and note the contents and the mucosal surfaces. Peel the keratinised layer on the mucosal surface of the gizzard. Examine the pancreas and cut open the duodenal loop. Cut open the other parts of the intestine, preferably the whole segments. Note the colour and consistency of the contents, colour and appearance of the mucosa. Open the caecal junction and the caecum at either side. Examine the colour, consistency and appearance of the mucosa and its contents. Open the trachea down to the syrinx. Closely examine the mucosa of the trachea by sliding the blunt portion of the knife or scissors at the opposite side.
 

Figure 18. Display stage in avian necropsy

Incise the lungs and note for any exudate and tissue masses. Remove the heart and make transverse section through it. Examine the kidneys, adrenals, ovaries/testes, and oviduct. Cut open the cloaca and examine its mucosa, contents and discharges. Locate the bursa of Fabricius and cut it open.

Dissect out the muscles at the posterior portion of the legs to expose the sciatic nerves. Do the same for the other leg and compare the size of the nerve. Note for any haemorrhage on adjacent tissues. Examine also the brachial plexus by cutting the muscles between the scapula and the vertebral column. Note for any enlargements of the nerves. Examine the muscles, joints and tendons of the legs and wings.

Remove the head from the rest of the carcass. Cut away the skin at the cranium. Using bone cutters or heavy duty scissors, cut the bones just behind the orbits and extend the cut caudally to the foramen magnum. Remove the cranial vault to expose the meninges and the brain. As in mammalian necropsy, fix the brain in 10% formalin solution prior to slicing. To remove the spinal cord, it is best to cut the dorsal arches of the spinal column, taking care not to damage the cord. Alternatively, severe the spinal column segment and fix them in 10% formalin prior to dissecting out the spinal cord.