Discuss with the diagnostic laboratory sample types required prior to PMEs. To minimise contamination, bacteriology samples should be collected from other tissues before opening the gastrointestinal tract. Submission of a piece of tissue ≥1 cm³ or a sterile swab may be appropriate. Sterilisation of the tissue surface using a heated palette knife may be required if contamination was unavoidable. Swabs may require prior incision into the tissue with a sterile scalpel blade. Samples for virology depend on knowledge of which tissues the aetiologic agent resides in.

Selection of tissues for histological examination depends on the case and gross lesions observed. In cases with no gross lesions or an uncertain diagnosis, suggested tissues for collection are outlined below. Many diseases may have significant histopathology but no gross lesions. Samples of any gross lesions should be taken from the edge of the lesion to incorporate normal and abnormal tissue. Excluding the brain and spinal cord, tissue samples should not exceed 1 cm thickness in at least one dimension (to enable rapid penetration of fixative) and, ideally, be immersed in 10 times fixative: sample v/v. If specific sample identification is required that may be difficult once removed (e.g. specific lymph nodes), place samples individually into labelled pots.

Autolysis occurs at different rates for each tissue type and must be taken into consideration when sampling. Intestine and pancreas autolyse rapidly and may not be useful for histological examination unless collected rapidly following death (less than 20–30 minutes). Freezing of carcases and/or tissues also significantly hampers histological examination.

Undertaking full PMEs and/or collecting full sets of samples in the field may be difficult. For problem-oriented minimal sampling for specific disease concerns, we recommend referral to the SRUCVS sampling guide (see references).

Recommended tissue collection for routine disease screening (in the absence of gross lesions/an obvious diagnosis) is given here.

As in other species, sampling of faeces and/or large intestinal content (caecum) can be useful for gut parasitology.

Samples of fresh liver and kidney should be collected into separate plain pots (a minimum of 10 g, but more if possible). These samples can either be refrigerated and sent for analysis quickly or frozen for longer term storage.

Vitreous humour is relatively stable, suitable for postmortem collection and useful for determination of calcium, magnesium, B-hydroxybutyrate and/or urea concentrations. Gently aspirate the sample using a large-gauge needle (14–18 g) inserted through the cornea or sclera into the posterior chamber of the eye. Centrifugation to remove contaminants prior to submission is recommended. Some laboratories will preferentially process aqueous humour samples, so consultation is required.

In fresh carcases, blood can be collected from the axillae/groin when stabilising the carcase, or from the heart, for use in zinc sulphate turbidity (ZST) tests (if not haemolysed) or serology, but not for biochemistry.

All pathological findings, internal and external (see below), should be recorded. Descriptions of lesions should include the location, distribution, number and/or extent (%), size, shape, colour and consistency/texture and for the cut surface. Additional details to record include ear tag numbers and identifying marks, species, sex, age, weight, body condition score and carcase postmortem condition.