EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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T h e B e a u f o r t c o t t a g e l a b o r a t o r i e s 46 Bone marrow aspirates These are not commonly collected from horses - only in cases that may have severe, undefined anaemia, severe persistent leucopenia or thrombo-cytopenia and in some cases of leukaemia. Samples are most commonly collected from the wing of the ilium, the ribs or the sternum. Sternal tap is recommended because it is most reliably productive. The ventral midline, under the sternum is clipped and prepared as if for surgical intervention. Local anaesthetic is infused into and under the skin of the ventral midline, just caudal to the olecranon, with the horse standing normally, restrained, sedated, in stocks. A bone marrow collection needle or an 18 gauge 3.5 inch spinal needle is introduced through a stab incision in the skin upwards to contact the sternum. The needle is then rotated with upward pressure until it enters the sternum, the stylette is removed and firm suction is used to aspirate a sample into a sterile 10 or 20 ml syringe, pre-treated with a few drops of 15% tripotassium EDTA to prevent clotting. The sample is transferred to EDTA tubes and labelled for laboratory examination, without delay. If delay is inevitable, smears should be made and fixed, to be sent alongside the wet samples, in case they are needed. The cytopathological examination of bone marrow smears requires specific experience. Normal and abnormal cell types are classified and their relative proportions assessed. The normal equine myeloid:erythroid (M:E) ratio should be 0.5-1.5. Semen samples Semen samples should be collected into an artificial vagina to allow a meaningful interpretation. In addition to a full case history, details of methods of collection, the colour, consistency, volume and motility of the ejaculate should be submitted with the sample. An undiluted semen sample should be sent in a sterile container for sperm density and bacteriological examinations, and a sample diluted immediately 1:1 with formol citrate solution for sperm live:dead and morphology examinations. Smear Samples Smear samples should, in general, be submitted already rolled onto a gelatincoated slide and fixed (‘Smear-fix’, carbowax or even hair spray) for specific cytological processing. Another undiluted and unfixed sample should be submitted in a sterile container or on a sterile swab in transport medium for concurrent bacterial culture. Endometrial smears Endometrial Smears are simple and quick to perform and provide a much more accurate and direct test for the diagnosis of acute endometritis in mares, pre-coitus than with swab examinations alone. When used in conjunction with endometrial swabs for bacteriological examinations, results are infinitely more meaningful, interpretable and therefore valuable. The presence of
G u i d e t o e q u i n e c l i n i c a l p a t h o l o g y endometrial epithelial cells is used as a test of smear quality and the presence or absence of polymorphonuclear leucocytes is used as the diagnostic test for acute endometritis. Smears may be collected during oestrus by a variety of methods, but we favour a simple non-guarded technique. An extended, sterile, large tipped swab is passed via a sterile speculum, through the relaxed cervix and rotated onto the endometrial lining. The swab is withdrawn and should be rolled onto gelatine-coated slides immediately and fixed with 'Smearfix', carbowax or even hair spray prior to transport to the laboratory for staining. Excellent results have been obtained by rolling smears onto 'Testsimplets' (Boehringer Mannheim UK Ltd.) pre-stained slides, then after two to three minutes at room temperature, washing off the background blue colour, drying and cover slipping. This technique provides an excellent permanent smear sample for immediate reading and/or for sending for a second opinion. Histology Using our state-of-the-art microwave processing system, same day results can be provided for most fixed tissue specimens. In general terms, equine lesions are best sampled, if possible and appropriate, by total removal and submission for histopathological processing and examination. If total removal is not possible, samples of representative size and location should be collected by wedge resection. Fine needle aspirates should only be collected if it is not possible to collect larger samples. Experience suggests that they often result in a traumatised lesion without a conclusive diagnosis and with a recommendation for the collection of a larger and more representative sample, delaying resolution. Total lesion removal is always preferable, if possible. Removed lesions or biopsies should be placed immediately into an adequate volume (10 x sample volume) of 10% formol saline. Reproductive tissues are best fixed in Bouin’s fluid because of their higher water content. Large lesions should be sectioned before submersion to allow adequate penetration of fixative. Sectioning should be performed with a thought to how the sample will need to be trimmed and orientated for histopathological processing to allow the pathologist to make a complete and meaningful appraisal. When sampling organs and tissues, we recommend that samples are taken from adjacent, grossly normal sites as well as from lesional sites. Notes of your own postmortem examination findings should be sent to aid histopathological interpretations. Samples should be carefully packed for transport to avoid leakages and breakages. 47
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EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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