This article was written by Elisha Frye, DVM, DACVPM and Erin Goodrich, DVM, DACVPM, Animal Health Diagnostic Center, Cornell University College of Veterinary Medicine. They can be contacted via email. Elisha Frye: eab73@cornell.edu and Erin Goodrich: elg25@cornell.edu
Building rapport with a veterinary diagnostic laboratory that is accredited by the American Association of Veterinary Laboratory Diagnosticians (AAVLD) is an important asset for bovine veterinarians. Dairy and beef herds of all sizes benefit from diagnostic testing, which can range from routine health surveillance to investigating disease outbreaks.
Full-service laboratories are typically comprised of multiple specialized laboratory units, which may include anatomic pathology, clinical pathology, bacteriology, molecular diagnostics, parasitology, serology, toxicology and virology sections. Veterinary diagnostic laboratories employ a wide range of technical staff, including board-certified specialists in the aforementioned fields. Their expertise can be utilized by field veterinarians for assistance with developing sampling and testing strategies, interpreting test results, and managing herd disease outbreaks.
When faced with a disease outbreak, collecting a history from the producer, examining the affected animal(s), and then contacting the laboratory before collecting samples is ideal, especially if there are necropsies to be performed on farm. Be sure to obtain herd size, vaccination status or relevant protocols, age (and stage of lactation, if applicable), group or pen affected, duration of disease, and physical exam findings.
Work with the laboratory to create a differential list and a set of specific samples needed to test for the pathogens or diseases on that list, to ensure that expectations for ancillary testing can be met. In general, serum or heart blood can be used for antibody testing, while swabs, feces, or tissues are used for antigen testing.
Sample Collection And Preservation For Submission
Cattle veterinarians should keep anaerobic and aerobic bacterial transport media and viral transport media on hand to aid in pathogen preservation during collection and shipment. Anaerobic transport media should be kept at room temperature once samples have been collected, while the other media can be refrigerated. Transport media are used for antemortem swabs when tissues are not available.
When performing a necropsy, fresh tissues are superior to swabs of tissues and should be submitted whenever possible. Take digital photos or videos of sick animals or gross necropsies and email them to the laboratory, especially for histopathology requests. When performing a necropsy, collect both fresh and formalin fixed samples of organs, focusing on gross lesions and organs that correspond to clinical signs.
Sample multiple areas of each organ (for example each liver lobe, each lung lobe and multiple sections of the GI tract). Individual fresh tissue should be placed in separate sterile, non-breakable, leakproof containers and labeled appropriately to avoid cross-contamination in transit and the potential for misidentification. (See Table 1 and the lists below for recommended tissues to collect.)
Fresh tissues should be at least 2 cm to 3 cm thick when possible; anaerobic culture can be performed when tissues are at least this size because they maintain an anaerobic environment. This can be especially important for tissue submitted from clostridial myositis cases, which often present as sudden death.
Depending on the client’s budget, and the course of disease, staged testing may be performed. For example, histopathology can be requested initially, followed by targeted ancillary testing based on the pathologist’s interpretation. The length of time it takes for different tests to be completed will impact the utility of staged testing and must be considered, especially if there is significant or ongoing morbidity or mortality in the herd.
Histopathology can take longer, as slides need to be made first and then read by a pathologist. Cultures and polymerase chain reaction (PCR) tests are typically quick tests, and results will usually be available within one to three days. Virus isolation or mycobacterial cultures are examples of tests that usually take longer to complete.
Veterinary diagnostic laboratories within the National Animal Health Laboratory Network (NAHLN) are able to test samples for specific pathogens, including those capable of causing high-consequence disease in food animals. These laboratories work closely with state and federal partners and can assist veterinarians who report cases of concern, allowing for early detection and response to emerging or foreign animal diseases. NAHLN laboratories are often the first to become aware of new and emerging diseases affecting livestock in the U.S. and may be testing for these pathogens frequently.
Accredited laboratories also send reportable disease results to state officials and work with state veterinarians on diagnostic algorithms. In addition, university-associated veterinary diagnostic laboratories typically perform research or work closely with researchers and may be able to enroll herds in studies or alert researchers and veterinarians to discounted testing for certain programs at the federal or state level.
Common Pitfalls Of Bovine Sample Collection And Interpretation
Providing a complete, concise signalment and history on the laboratory submission form is important, and diagnostic lab staff do read them. Recent vaccination, sample handling, and immune status can all impact test result interpretation.
Modified live vaccines (both injectable and intranasal) may be detected by PCR for weeks in nasopharyngeal swabs, transtracheal washes, whole blood or tissues, depending on the product administered, the sample tested, and the virus or bacteria of concern. This can complicate result interpretation but needs to be considered, so it is important to list vaccination product and dates of administration on diagnostic submission forms. Additionally, maternal antibodies, vaccine-induced antibodies, and antibodies produced in response to infection, are all detected by most serology tests, and cannot be readily differentiated.
Information regarding the species, the sample site and previous antimicrobial administration is important to include in the history portion of the submission form. This can inform some of the processes taken in the laboratory to maximize the likelihood for pathogen detection and diagnosis.
Fresh tissues can be frozen, and this will preserve pathogens for most ancillary testing, especially if staged testing is anticipated or if samples are collected on a weekend and cannot be mailed overnight. One exception is feces for floatation for gastrointestinal parasites; this should be held in the refrigerator rather than frozen.
When trying to diagnose septicemia postmortem, submit fresh samples of lung, spleen, lymph node and kidney (or at least two of the four organs) for aerobic culture.
Submitting an entire carcass or carcasses to a diagnostic lab for full necropsies can be ideal for cases that require assessment of the entire central nervous system, as removal of the brain and spinal cord in the field can be daunting. This is also a good option if multiple field necropsies have not yielded sufficient diagnostic results to determine the cause of death(s).
Whenever the diagnostic test results are surprising and do not fit well with the clinical presentation, consult with the diagnostic laboratory, as the sample type or quality may have impacted results. Laboratory staff want to hear about these situations, because it may signal an issue with their test and prompt double-checking or re-running a sample – though internal positive and negative controls and other protocols are in place to minimize these issues.
Laboratory employees can also assist with trouble shooting other aspects of the case that may have impacted the result, to help improve the next submission, which benefits both the veterinarian and the producer.
