Sampling tips for large animal vets


Here are some tips from our pathologists that may be useful during sample collection or out in the field.

1. For PCR, dry swabs are preferred over transport media swabs. We have had success with transport media swabs but the material you collect on the swab is diluted by the media and there is a risk of missing what is there.  If only transport media swabs are available, use the swab, but put it in a sterile tube instead of back into the media for transport to the laboratory. If cost is an issue, you can pool swabs in some situations e.g. three swabs of conjunctival exudate pooled for IBR PCR.

2. EDTA blood is the required sample for MCF PCR testing in live animals. The virus is cell-associated, hence the ideal of whole blood. If you forget to take EDTA, or are caught without EDTA tubes, we can test serum but a negative result could have you wondering whether the result is truly negative. At post-mortem you can take a lymphocyte-rich tissue to test by PCR (lymph node, spleen) as well as a good range of histology samples (brain included).

3. Diagnostic testing for Mycoplasma bovis —samples for PCR might include milk in cases of mastitis, joint fluid in cases of arthritis, and pneumonic lung. If a sample is positive, we are unable report the result directly to you. We are required to report instead to MPI and they will confirm the result with their own testing and report to you. This is obviously important if MPI need to put controls on a herd or slaughter a herd. The sensitivity of the test for clinical material is good. We are also allowed to test clinically healthy animals (e.g. tonsillar swabs) but the sensitivity of the test for detecting carriers is poor. We do not have an antibody test for M. bovis.

4. Summer is typically when we see outbreaks of Pasteurella multocida septicaemia in calves. The septicaemia is manifested as fibrinous peritonitis, pleuritis, and pericarditis (all three together or a combination of two of these). Pneumonia is uncommon but has been seen in the odd case. Sporadic bovine encephalomyelitis (SBE) may also inflame these serosal surfaces in some calves, but cases to date have largely been clumps of exudate rather than the widespread fibrinous exudate of Pasteurella. As soon as you see polyserositis in a calf post-mortem, take a transport media swab of the exudate for bacterial culture. If concerned about SBE, take some exudate for PCR (and the brain for histology). These suspect cases also benefit from correlation of the microbiological findings with the histological findings of the lesions and major organs.

If you are ever unsure about the appropriate sample to take for any test, simply refer to our current price book, search our website or give us a call—0800 GRIBBLES.