Veterinary Handbook Disease Finder

Veterinary Handbook Contents

11.1 Stages Of The Ruminant Necropsy

11.1.1 Animal Characterisation And History Collection

Obtain a history. A good history examination will direct focus on certain elements of the necropsy. This is important if time is limited.

  • Record signs, symptoms and duration of illness that were observed in the animal to be necropsied and herd/flock mates.
  • Record the numbers of herd mates affected, recovering and dying, and what type of animals were affected including their age, sex, breed, physiological, nutritional and vaccination status.
  • Record when and where the animal became sick and died.
  • Record the management, environmental and animal risk factors that may have combined and contributed to the death, over the days or weeks leading up to the time of death.

Examine sick animals systematically before they are killed.

  • Record clinical information such as blindness, weakness, ataxia, jaundice, diarrhoea, respiratory distress and rectal temperature.
  • Note that elevated rectal temperature may indicate acute infection, exertion or hot and humid environmental conditions.
  • If an exotic or emergency disease is suspected, the relevant government veterinary service must be notified immediately.
  • If anthrax is suspected, don't create or spread spores by opening or moving the carcass until anthrax is excluded by rapid immunochromatographic test, blood smear or blood culture.
  • If hyperthermia (heat stroke) is suspected, measure core temperature as soon as possible after death. Make a stab incision in the skin of the paralumbar fossa and force a probe thermometer through the muscle layers into the abdominal cavity. The ambient temperature and time of death should be noted.
  • Samples that may be of value from animals prior to death or euthanasia include: serum, plasma and unclotted blood samples (plain, lithium heparin and EDTA tubes, respectively). If possible, blood and faecal samples should be collected from both affected and unaffected herd mates.

11.1.2 External Assessment

Get in the habit of always thinking the worst first! Is this an exotic disease like foot and mouth disease? Could it be a zoonotic disease such as anthrax or Hendra virus infection perhaps? Consider precautions as appropriate to protect other animals and people (including yourself) from risk of disease transmission.

Examine the carcass and record its characteristics including the following:

  • Identification such as NLIS tags, management tags, tattoos, earmarks, brands etc.
  • Weight in kg - have an experienced person assist in estimating weight if necessary.
  • Condition score on a 1 to 5 scale; 1 being emaciated, 2 being backward store condition, 3 being store condition, 4 being forward store and 5 being fat.
  • Hair coat length - is it a short summer coat, medium, or a long winter coat.
  • Extent of postmortem decomposition.
  • Age based on brands, owner information or teeth eruption.
  • Sex
  • Breed
  • Any postural predicament and whether the animal died quietly or after struggling.
  • Take a digital photograph of the undisturbed carcass including a close up of the ear tags, brands, tattoos or other case identifiers. The lid of a sample container placed on the carcass can be used to display the case number for a photographic record. Later when images are downloaded to a computer, include the case number or other animal identifiers in the file extension.
  • Take photographs of any lesions and abnormalities.
  • Cut out NLIS and management tags, clean, then place them in a container of buffered formalin into which histology samples from the animal will be stored.
  • Label any containers with the owner's surname, date and animal identification or case number, using indelible ink.

Examine the external organs in the following sequence.

  • The head - eyes, conjunctiva, nose, ears including ear canal, mouth including lips, gums and tongue for erosions, ulcers, blisters or discolouration.
  • Make an initial estimate of the age from the eruption and wear of incisor teeth.
  • The skin, especially for external parasites.
  • Neck, superficial lymph nodes, ribs, flanks, ventral abdomen, prepuce, anus, vulva, tail.
  • The limbs, especially for wounds and swellings, including interdigital spaces, coronets, joints.
  • If anthrax, tick fever or a blood disorder is suspected, cut off the tip of the lower ear and make a blood smear on a glass slide. Place the ear tip in the ear canal of the upper ear so that it stays with the carcass for proper disposal.

Samples that may be of value from freshly dead animals include serum, vitreous/aqueous humour, and a faecal sample.

  • Collect serum by collecting whole blood into clot retracting tubes and standing the blood tube vertically at room temperature for 2-4 hours to allow the clot to retract. The serum can then be decanted into a sample tube, labeled and frozen. The red cells can be discarded.
  • Collect vitreous or aqueous humour in cases of sudden death or when it is not possible to collect a blood sample. Useful clinical chemistry information may be obtained.
  • Vitreous humour is best collected by inserting a 16 gauge needle at the junction between the sclera and cornea, and using a small syringe to extract the vitreous from the posterior chamber. For aqueous humour, use a 20 gauge needle inserted into the cornea at the limbus (the white of the eye), to extract fluid from the anterior chamber. The vitreous and aqueous humour samples should be labelled and stored frozen as per serum.
  • In the event of unremarkable or equivocal gross and histological findings, these samples may prove valuable when subjected to clinical pathology testing to determine nutritional status and identify specific organ dysfunction.
  • Consider collecting ectoparasites (if present) and swabs of any discharges.

11.1.3 Initial Dissection And Display Of Body Cavities

The aim of this stage is to dissect the carcass to display but not disturb the contents of the oral, thoracic and peritoneal cavities as shown in Figure 11.1. The carcass should preferably be necropsied on a clean surface to minimise contamination. Conventionally, ruminants are necropsied in left lateral recumbency (left side down). The rumen and spleen then lie underneath the intestines and rumen, respectively. Relocate or roll over the carcass if necessary and possible.

Note that variations to the following sequence may be warranted for certain conditions when delay causing postmortem changes must be minimized to assist correct interpretation. For example, if enteritis is suspected, exteriorise and examine the intestine as soon as the abdomen is opened and collect samples for histology and microbiology if required.

The typical sequence is as follows:

  • Reflect the upper front limb by cutting through the skin and muscles of the armpit. The reflected armpit will serve as a table. When the skin is highly valued, incisions can be made along the ventral midline of the abdomen and along the medial midline of the limbs.
  • Incise the skin by inserting and sliding the point of the blade under the skin and along the subcutaneous tissues then pulling the blade upward or outward. This cuts between the hairs and skin surface grit and helps to preserve a sharp edge.
  • Reflect the upper (right) hind limb by cutting through skin and muscle of the right groin to expose the hip joint.
  • Incise the joint capsule, sever the teres ligament and dislocate the hip joint by forcing the leg back and reflect the hind leg in the same way as the foreleg.
  • Make a cut down the length of the femur to expose the diaphysis for later sampling of bone marrow. The reflected inner thigh and cut will serve as a platform to temporarily lay your knife if required.
  • Skin the right side chest and abdomen starting with an incision along a line at a level connecting the middles of the humerus and femur prior to their reflection.
  • Reflect the skin as far ventrally and dorsally as possible to serve as specimen trays if required.
  • Skin the right side neck and head. The incision should run in a line from the level of the armpit to the tip of the mandible.
  • Reflect the skin dorsally and ventrally to expose the jugular groove, trachea, molars and submandibular area. Preserve the ears to serve as handles later when performing detailed examination and sampling of the head.
  • Cut the mandibular symphysis with the rib cutters and retract the separated lower jaws laterally to expose the oral cavity, teeth, and hard and soft palates.
  • Expose the abdomen by cutting the right side wall of abdominal muscles along the caudal margin of the ribs, then along the lumbar muscles and continuing to the anterior midline attachment at the pubis of the pelvis. The muscle mass is then reflected ventrally to expose the abdominal contents, the wall of muscles being hinged in the ventral midline. There is less likelihood of puncturing abdominal viscera if the abdominal muscles are removed in this way, rather than by commencing with a ventral midline incision.
  • If gastrointestinal disease is suspected, take samples at this point to minimise postmortem changes.
  • Cut the bony pelvic floor in two parallel cuts with rib cutters to remove a 2 to 3 cm strip of bone from the pelvic floor to expose the pelvic canal.
  • Cut the right diaphragm along its outer margin and observe if the lungs collapse. Failure of the lungs to collapse signals the possibility of respiratory disease.
  • Remove the right rib cage to expose the thoracic cavity by cutting along the ventral and dorsal margins with rib cutters. The rib cage can be placed beside the carcass to serve as a table for inspecting viscera.
  • Loppers (rib cutters) can be used to cut ribs, mandibular symphysis, pelvic floor and between vertebrae and sternebrae of most farm animals. Geared loppers with a bypass action rather than anvil action are best.
  • If using a knife to remove the rib cage, this is done by cutting through the soft cartilage of the costochondral junction near the sternum. The costochondral junctions are best cut from the inside out because this allows the knife to naturally find the joint and it prevents cutting into the underlying heart and lungs. The costochondral junctions of the first two ribs run at a sharp angle to the line extending along the joints of the other ribs, requiring a change in cutting direction toward the neck when they are reached.
  • When the costochondral junctions have been severed, the intercostal muscles can be cut to separate individual or groups of ribs from each other. These are easily levered back so that the ribs are broken close to their insertion in the vertebral column. Pliability and fragility of the ribs can be checked while doing this. Bone quality here is reasonably representative of bone quality in the remainder of the skeleton.
  • Reflect the tongue and larynx caudally to expose the oropharynx cutting the joints or bones of hyoid apparatus with knife or rib cutters, respectively, to free the larynx.
  • To cut between the hyoid bones with a knife, locate a hyoid joint by palpating two hyoid bones joining at an angle. Insert the knife into the angle and let the blade find the soft cartilage of the joint by lifting the blade into the angle formed between two hyoid bones. Image

Figure 11.1: Opening the carcass to complete the initial dissection and display stage

At this stage, major dissection has been completed as shown in Figure 11.1.

  • Step back and carefully overview the opened carcass noting any accumulations of fibrin or fluid in cavities (including the pericardial sac), the state of nutrition, or presence of any carcass discolouration.
  • For visible organs note any adhesions or displacements, the distribution and extent of any lesions and any abnormalities of size, shape, surface, sound, smell, colour, contour, consistency and content.
  • Take a photograph of the carcass as a whole and then each of the exposed body cavities.
  • Take close-up photographs of any changes in organs that you think are important.
  • Collect samples of any abnormal fluids.

11.1.4 Detailed Examination And Sampling

Now begins a systematic process of close examination, description and sample collection.

The sequence will be:

1. The abdomen

2. The oral cavity and neck

4. The thorax (chest)

5. The abdomen revisited

6. The head revisited

7. The feet and limbs

8. The spinal column

Image

Figure 11.2: Necropsy sequence for detailed examination and sampling

This sequence, which is shown in Figure 11.2, is recommended for two reasons. One, it ensures the organs and tissues are examined and sampled in order of increasing susceptibility to autolysis and contamination. Two, it is logical, efficient and therefore easily remembered and repeated.

Samples and photographs of all lesions and abnormalities should be collected as you go.

11.1.4.1 The Abdomen

As a general guide, it is best to open fluid filled organs and hollow viscera after solid organs have been sampled to avoid contamination.

  • Tear the omentum and find and expose the duodenum and then the pancreas (embedded in the mesentery adjacent to the duodenum) and collect samples if required.
  • Squeeze the gall bladder to check the patency of the bile duct carrying bile into the duodenum
  • Palpate the duodenum, jejunum, ileum, caecum, colon and rectum along their length.
  • The ileum, caecum and colon can be fanned out over the abdomen and lumbar region for closer systematic inspection and sampling if necessary. They can then be flipped over and the jejunum examined.
    • Reddening of intestines alone does not mean that enteritis or enterotoxaemia is present. Simple postmortem change can cause this. Thickening of the intestinal wall, watery or bloody contents and enlarged, oedematous draining lymph nodes will be present to some degree in enteritis.
  • Examine the omentum and mesenteries including mesenteric lymph nodes, hemisecting at least three lymph nodes to examine cut surfaces.
  • Cut the attachments of the small and large intestines to the carcass (which are the root of the mesentery and to the liver) and remove, thereby exposing the forestomachs, bladder, kidneys and internal reproductive organs.
  • Segments of the intestine should be opened to allow inspection of the inner surfaces and contents.
  • Samples from the intestinal tract that may be of value include:
    • Swab of intestinal contents. Pass a sterile swab into the lumen of the intestine and rub the swab head firmly against the mucosal wall as this is where enteric pathogens will be most concentrated.
    • Samples of intestine collected into formalin for histology. Do not scrape the lining of the intestine with a knife to clean away faeces for samples that will be submitted for histology as the scraping will damage the microscopic villi.
    • Loop of intestinal contents for culture of uncontaminated contents. Form a U-shaped loop of intestine, and tie the top of the U together with string. This way, only one tie-off point is required. A length of ileum is often collected this way for Johne's disease culture.
    • Always collect a sample of ileocaecal valve for histology (into 10% buffered formalin).
  • Palpate the forestomachs (rumen, reticulum, omasum) and abomasum, spleen, liver and duodenum.
  • Cut the dorsal mesenteric attachment of the viscera to the abdominal wall so you can roll the stomachs, spleen, liver and duodenum out of the abdomen.
    • Before making the cut to the dorsal mesentery, palpate the adrenal gland at the anterior pole of the right kidney and endeavour to leave it attached to the carcass.
    • Cuts are then made in the dorsal mesentery through the pancreas and the diaphragm.
    • Make stabs in the rumen wall to form handholds to help roll the viscera.
    • Roll the forestomachs out of the abdomen so that the spleen and liver are on top, out of the manure.
  • Palpate and slice the spleen in situ.
  • Inspect and palpate the liver before dicing each lobe and examining cut surfaces. Always collect samples of liver for histology, preferably a sample from each lobe. Collect samples for toxicology or culture if required.
  • Incise the gall bladder to examine the mucosa and bile.
  • After the spleen, liver and gall bladder have been examined, lay out the stomachs for systematic examination and sampling.
  • The lining and contents of rumen, reticulum, omasum and abomasum can be inspected and compared by incising along the ventral aspect of the abomasum and forestomachs in one continuous cut.
    • Measure pH of rumen content with a test strip. Normal pH should be >5.9. If the sample is taken from a very recently dead animal and the pH is <5.5, ruminal acidosis is present.
    • Collect a sample of rumen content if required.
    • Always collect a sample of the ventral wall of the rumen including a pillar for histology. The mucosa of the ventral rumen rather than the dorsal rumen is more likely to exhibit lesions and should be collected for histological examination.
    • Inspect the contents of the reticulum for foreign bodies such as wire or lead. Collect a sample of reticulum wall if required.
    • Inspect the abomasal mucosa and contents by cutting along the greater curvature through the pyloric valve into the duodenum. Look closely for worms by gently scraping clean the mucosal surface with the back of your knife. Examine the abomasal folds and duodenal mucosa collecting samples if required.

11.1.4.2 The Oral Cavity And Neck

  • Examine the pharynx and exterior of the larynx and tongue before dicing the tongue.
  • Separate the oesophagus and trachea from the carcass to the level of the first rib but maintain their connections to the tongue and larynx.
  • Expose and examine the thyroids, attached to the proximal trachea.
  • Starting at the dorsal larynx, incise the length of the trachea and examine and sample as required.
  • Incise the length of the oesophagus and examine and sample as required.

11.1.4.3 The Thorax

  • Incise the pericardium and note the presence of any fluid or exudates.
  • Prolapse the heart out of the pericardium and closely examine the surface of the heart.
  • Palpate the lungs then sever their dorsal and ventral attachments to the thorax keeping the heart attached to the lungs to form the "pluck".
  • Remove the "pluck" for inspection.
  • Inspect the epicardium (outer surface of the heart) and inner surfaces of the pericardium. Petechial and ecchymotic haemorrhages on the epicardium are a normal agonal change related to terminal asphyxia.
  • Separate the heart from the pluck by severing the great veins, aorta and pulmonary artery at the base of the heart, well distal to the aortic and pulmonic valves.
  • Cut across the heart about 1/3 of the way up from the apex (pointed distal end of the heart away from the atria). Examine the myocardium then collect a 1cm thick cross-sectional slice of the heart adjacent to where you cut across the heart. This slice contains right and left ventricular wall and the interventricular septum for histology, and allows comparison of the thickness of the free walls of the right and left ventricles which should be in the ratio of 1 to 4.
  • Next progress to opening the heart by incising vessels, valves and chambers in the direction of blood flow from the posterior vena cava to the aorta.
    • With the right side of the heart uppermost, cut transversely through the right atrium, remove blood clots and inspect the right atrioventricular valve and the inflow tract from posterior vena cava to atrium.
    • Cut open the right ventricle close to the septum from the apex end through into the pulmonary artery and examine the outflow tract and pulmonary valves.
    • Roll the heart to place the left side uppermost and cut transversely through the left atrium and inspect the left atrioventricular valve.
    • Cut open the left ventricle through the aortic valves into the aorta and inspect the outflow tract.
    • Finally, "bread slice" the heart to adequately examine the interventricular septum and myocardium.
  • Inspect the surfaces of and palpate both lungs.
  • Estimate the percentage of lung volume affected by pneumonic lesions if present.
    • Red discolouration alone does not mean that pneumonia is present. Normal lungs feel spongy while oedematous lungs and some viral pneumonias feel rubbery. In other pneumonias the affected lung is consolidated and feels like liver. Consolidated lung, indicative of pneumonia, sinks in formalin.
  • Incise the trachea through to primary and secondary divisions of bronchi.
  • Always collect lung tissue for histology from the cranioventral, middle and caudal lung lobes, and tracheal tissue if required.

11.1.4.4 The Abdomen Revisited

  • Locate adrenals adjacent to the anterior pole of the kidneys and excise and hemisect both adrenals and inspect cut surfaces.
  • Incise both kidneys longitudinally in situ and inspect cut surfaces.
  • Always collect a sample of kidney including both cortex and medulla for histology. Collect large samples for chemical or toxicological analysis, if required.
    • Soft friable (pulpy) kidneys are not proof of enterotoxaemia (aka pulpy kidney) and are a common postmortem change, especially in hot conditions. Enterotoxaemia is a disease of young (<12mo) unvaccinated ruminants eating large amounts of high quality feed.
  • Blunt dissect the kidneys and gently pull away from the body wall to assist tracing of the attached ureters to the neck of the bladder.
  • Collect a urine sample by aspiration (needle and syringe) from the bladder and test for pH, ketones, glucose, protein, nitrite, blood and leucocytes using a test strip.
  • Cut open the bladder and inspect the mucosa.
  • Remove and inspect female and male genitalia as required.
  • Abortion investigations require the uterus, and iliac lymph nodes to be sampled for culture. Pregnant or fluid filled uteri should be dissected free after the oviducts and cervix have been tied off with string.
  • The age of the bovine or ovine foetus can be roughly estimated using the following formula: Measure the crown-rump (CR) length in inches, multiply by two, then take the square root of the resultant number. This gives the gestational age in months.
  • Palpate the udder to detect gross lesions.
  • Incise and inspect the four quarters of the udder, major milk sinuses and teats collecting samples for culture and histology if necessary.

11.1.4.5 The Head Revisited

  • Before removing the head at the atlanto-occipital joint collect a sample of cerebrospinal fluid (CSF) and spinal cord at C1.
    • Collect CSF through the ventral aspect of the intact atlanto-occipital joint using a vacutainer and 22g needle. Or collect a swab after exposing the joint with a stab incision with a sterile scalpel blade.
    • Collect a 2cm length of spinal cord from the opened joint while the joint is being levered open by extending the neck.
  • The head can now be disarticulated and severed at the atlanto-occipital joint.
  • Examine the eyes and excise if necessary. Eyes are easily removed by first removing the eyelids. A boning knife is then used to cut around the rim of the orbit to loosen the eye. This enables the eye to be prolapsed with the aid of the handle of the tissue forceps. Once the eye is prolapsed, it is kept under tension while its attachments are severed.
  • Aqueous humour and vitreous humour can be obtained from one eye. The other uncollapsed eye can be submitted in formalin for histology.
  • Section the masseter muscles, examine the mandibles, teeth, buccal mucosa, tonsils and retropharyngeal lymph nodes.
  • Removal of the brain and pituitary gland should be considered if there was a history of nervous signs, if there was a suspicion of enterotoxaemia (excessive rumen contents and little other changes on gross necropsy), or if gross necropsy did not provide any indications of likely diagnoses.
  • If only the brainstem is required, sample it via the foramen magnum using a modified spoon. The brainstem would be required in cases where there were no significant history or postmortem findings suggestive of cause of death and where complete brain removal was difficult or not possible.
  • Sever the ears to expose the middle ear and examine for exudates and mites. Do this last as the ears serve as occasional handles up to this point.

11.1.4.6 Brain Removal By Longitudinal Craniotomy

Examination of the brain is essential for the diagnosis of central nervous system diseases.

The longitudinal craniotomy is a simple method of removing brains of sheep and cattle in the field. It is just one of a number of techniques that can be used - all have advantages and disadvantages.

Longitudinal craniotomy involves splitting the skull, but not the brain, ventrally and dorsally along its longitudinal axis with a hatchet (Figure 11.3). The hatchet can be hit with a mash hammer for greater control and safety. Eye protection should be worn. The two halves can be levered open from the front end to expose the intact brain.

ImageImage

Figure 11.3: Cuts and leverage required to complete the longitudinal craniotomy method of brain removal

This method requires practice. It has the advantage of exposing the pituitary gland. The technique is similar for sheep, goats and cattle.

The procedure can be performed quickly, simply and safely under field conditions with minimal equipment. With practice the brain can be removed in less than one minute.

The equipment required includes a hatchet, mash hammer, boning knife, disposable rubber gloves and safety glasses.

  • Once the head is severed, skin the ventral head and remove the tongue and soft tissues of the throat so as to expose the hard palate and ventral cranium.
  • Split the mandibular symphysis with the hatchet or rib cutters if not done already and lever the two halves apart.
  • Turn the head over and stabilise it on the ground by maneuvering the anterior maxilla onto the ground between the spread lower jaw bones.
  • Cut the skin on the top of the head along the midline.
  • Extend the cut deeply into the soft cartilage of the nose in the midline to split the nose.
  • With a hatchet, crack the dorsal skull along the length of the midline where the skin cut has been made. The hatchet can be hit with a mash hammer for better control.
    • The aim is to fully cut through the depth of the nose and jaw, and extend the cut back to crack the cranium (bony case surrounding to brain) without resulting in damage to the brain. 
  • Turn the head over and use the hatchet to finish splitting the hard palate and nose to full depth and crack the ventral cranium along the midline.
  • With a knife, cut any soft tissue attachments that might prevent the two halves of the head being levered apart.
  • Grab the two halves of the split nose and slowly prise and pull them apart.
  • Use the hatchet to continue cracking bone if the head won't come apart easily. Once the cranium has been cracked sufficiently, the whole head can be levered open and the brain and pituitary gland exposed.
  • A boning knife or scissors are used to cut the nerve roots, dura mater and the tentorium cerebelli as the brain is exposed and removed.
  • The tentorium cerebelli is a piece of ligament-like meningeal tissue that divides the cerebellum at the back of the brain from the cerebrum at the front of the brain. In cattle it is very tough and needs to be cut if the brain is to be removed intact. It is less of a problem in sheep.
  • The hemisected pituitary gland is exposed at the base of the brain and is easily removed.

Common mistakes include:

  • Cutting too deeply into the bone around the brain, particularly the bone protecting the ventral brain, can damage the brain stem.
  • Insufficient 'cracking' of the bones surrounding the brain, particularly the ventral cranium, can make it difficult to lever the cranium apart.
  • One side of the nose breaks when levering the two halves of the nose apart.
  • Levering the head apart too quickly can tear the brain.
  • Not cutting the tentorium cerebelli in cattle causing the brain to tear when attempting to roll it out.

11.1.4.7 Examine The Feet And Limbs

  • Closely examine soles, white lines and the interdigital space of all four feet for lesions.
  • Palpate all limbs, especially joints, for swelling and crepitus and cut into these areas if found.
    • Lameness and swelling of the leg where no obvious skin or interdigital wound is apparent may be caused by small punctures of the sole or white line. Bacteria enter causing sepsis which extends beneath the sole, tracking up the hoof wall and up the leg.
  • By the end of the necropsy, at least four joints should be examined.
    • The coxofemoral joint will have been opened during the initial dissection and display stage.
    • Three other joints amenable to routine examination are the carpal, scapulo-humeral and stifle joints. The carpal joint, being a compound joint, is more susceptible to blood borne infection and should always be examined.
    • The stifle joint is best opened by cutting the dorsal and medial patellar ligament and reflecting the patella laterally. Then cut the medial joint capsule so the joint can be levered open.
  • Collect samples for culture if required. To ensure an uncontaminated sample, sterilise the outside of the joint with a spatula heated with a gas torch prior to cutting into the joint with a sterile scalpel blade.
  • Incise major muscle masses of upper limbs and back. Rump and neck muscle may be examined for injection site trauma.
  • Collect peripheral nerves if indicated by history or protocol.
    • The sciatic nerve can be found between planes of large muscle behind the femur by blunt dissection. The tibial and peroneal branches of the sciatic nerve can be easily found by skinning between the gastrocnemius tendon and the tibia. The brachial nerve can be found by exposing the lateral aspect of the lower humerus. Smaller peripheral nerves run with an artery and vein which helps fix their location.
  • Gross assessment of bone marrow can be done quickly and easily by cracking open the shafts of long bones with a mash hammer. By dissecting down and around the diaphysis of the femur of the reflected hind leg, then torsing the femur by twisting the lower leg, a spiral fracture can be created when hit with the hatchet or mash hammer. The bone marrow is then easily examined, and if necessary photographed and sampled, along the length of the diaphysis.
    • Animals that are mobilising fat reserves will show a watery or gelatinous appearance to the marrow fat.
  • Bone marrow can also be collected from a longitudinal slice of a sternebrae (one of the bony segments of the sternum) centred on the red cancellous bone between the cartilaginous or solid ossified areas. Use rib cutters to remove a 3-4 mm thick slice and place in buffered formalin for histology. This sample fixes well and in the laboratory, does not take long to decalcify. Alternatively, the ends of ribs, close to costochondral junctions can be shaved off with a sharp knife and placed in buffered formalin.

11.1.4.8 The Spinal Column

  • Cut between individual cervical, thoracic or lumbar vertebrae with a hatchet and light mash hammer and dissect free with a knife.
  • Lumbar vertebrae are easy to remove. Thoracic vertebrae require ribs to be cleared away but this is a relatively simple task.
  • Remove the spinal cord from each vertebra by snipping nerve roots and meninges with scissors and pushing it out with the open end of a needle cap or the plunger from a 2mL syringe. Place samples in buffered formalin.
  • Sampling need only occur if there are clinical signs referable to the spinal cord.