The emergence of porcine circovirus type 2 (PCV2) in the Midwest in the last year has forced producers to refocus on the nursery and finishing phases of production. We continue to battle a wide range of preexisting pathogens, including porcine reproductive and respiratory syndrome (PRRS), swine influenza virus (SIV), Mycoplasmal pneumonia, Haemophilus parasuis, Actinobacillus suis and Streptococcus suis. And Porcine Respiratory Disease Complex (PRDC) is a bigger economic issue than ever.
When mortalities occur on any farm, the postmortem (posting) exam may be the most valuable tool in determining the cause of pig deaths. It allows us to make a quick, initial diagnosis of the pathogens that may be involved so an early treatment protocol can be put into place. A diagnostic laboratory then confirms this initial diagnosis.
The pathology report that you receive from the diagnostic laboratory contains a large amount of information, including the presence of viruses, bacteria and parasites, plus bacterial sensitivities and histopathology reports (microscopic changes in the tissues) that help to determine whether or not the pathogens found are significant.
We consider tissue submissions to be a very good diagnostic investment due to the amount of information received relative to the expense. Polymerase chain reaction (PCR) tests and virus isolation results also provide a source of virus that can be used for additional sequencing information to help characterize the strain or subtype of virus present. The control program often requires this specific information.
Information from the pathologist's report then drives the treatment recommendations and future diagnostics. Bacterial antibiotic sensitivity reports indicate which antibiotics should be effective in controlling bacterial pathogens that are causing problems. Your veterinarian can develop a treatment protocol using this information, coupled with his knowledge of the antibiotics that will effectively reach the target organs. In cases where the sensitivity report shows that multiple antibiotics are available and appear to be effective in pigs, the decision-making process may include a cost comparison.
Injectable antibiotics are the most important part of any treatment protocol involving bacterial pathogens, but water-soluble and feedgrade antibiotics may also be used in the treatment program.
Additional diagnostics, such as serum profiling of different age groups, might be useful to identify the age when pigs are becoming infected. This information can be helpful for prevention and control strategies.
The diagnostic lab's report may be even more valuable in a consistent flow of pigs when it is used to take preventative actions in younger groups to “get ahead” of problems before they occur. Preventative actions might include changes in management or pig flow, changes in vaccination protocols or the use of strategically timed medication programs, to name a few.
When your veterinarian arrives to post pigs and collect tissues for the diagnostic laboratory, a complete history should be taken. This history gives the diagnostic laboratory background information on the group of pigs, and serves as a good way to review what actions the producer has taken. It can also help guide future interventions based on the effectiveness (or lack of effectiveness) of these past interventions. It may also uncover something that has been missed.
The diagnostic laboratories' tissue submission form can serve as a guide in taking this history, which should include:
The age of the pigs submitted;
The date and time of pig death;
Whether the submitted pigs were euthanized;
The number in the affected group, including the number of pigs that are sick and dead;
The duration of the problem;
The type of housing;
Any treatments or vaccinations the pigs have received;
Major clinical signs and clinical diagnosis; and
A description of the postmortem findings.
Realizing that postmortems and tissue collection can help zero in on the cause and effective treatment of a herd health problem, following are five pitfalls to avoid when conducting those examinations:
- Failure to conduct postmortem examinations.
Veterinarians are specifically trained to effectively conduct postmortem exams; however, producers and managers are often called upon to assist with collecting, preserving and shipping samples for laboratory analysis.
Due to the large scale of many hog operations today — both in numbers of pigs and geographically — it is not always possible for a veterinarian to get to the site to conduct postmortem exams in a timely manner.
For producers who are interested in learning proper posting procedures, it is critical to spend time with a veterinarian to learn pig anatomy and effectively collect samples. Some veterinarians have found it helpful to have producers accompany them to a packing plant to do slaughter checks. This is a good way to see a lot of normal anatomy and, possibly, some abnormal anatomical conditions.
Digital cameras have been useful tools for producers to e-mail pictures of posted pigs for a conditional opinion. Digital photos and the color calibration of computer monitors present some major challenges to overcome, but some gross analysis can be made in specific circumstances.
In difficult cases, pigs can be delivered directly to the diagnostic lab to get the very best results, since there is no delay between postmortem and testing of the tissues.
Some causes of mortality are easier to diagnose than others. Submitting the proper tissues in adequate quantities to the laboratory increases the odds that the correct pathogen is identified. If a diagnosis has previously been made, posting pigs can help verify whether the diagnosis was accurate or if circumstances have changed.
As a rule, the most accurate results will be achieved when your veterinarian conducts the postmortem exam and submits the tissues to the diagnostic laboratory to confirm a preliminary diagnosis.
The veterinarian will follow up with the results of the laboratory diagnosis, and present an action plan to treat or manage the problem and/or prevent future occurrences. It is a mistake not to post pigs. We must try to learn from past failures (dead pigs) to succeed in the future.
It is vital to identify groups of “at risk” pigs quickly. New tools are becoming available to help monitor groups of pigs to quickly identify increased mortality so that postmortems and corrective action can be taken to reverse a bad trend.
Figure 1 is an example of Metafarms' Mortality-by-Week-on-Feed report. It shows a dramatic spike in mortality in the fourth week after pigs are placed in finishing. Real-time recordkeeping systems such as this are helpful for monitoring losses in large systems.
- Failure to post the “right” pigs.
Groups of pigs with a high mortality rate can look dramatically different from one group to another. Some mortalities occur as “sudden” or “unexpected” events, where apparently healthy pigs are found dead the next day.
Pigs in another group may have more warning signs and, by the time they die, appear more as chronic cases. In those cases, it is tempting to simply post the dead pigs and submit tissues. However, the diagnosis from these pigs may be different from what caused the initial problem.
Chronic pigs may have more secondary infections, and may have received antibiotic treatments that inhibited growth of bacteria at the lab. In that situation, it may be necessary for economic reasons, as well as for the welfare of the group, to sacrifice pigs that are showing clinical signs of early disease progression.
It is rarely rewarding to submit tissues from pigs that have been dead for longer than 24 hours (and even less in hot weather), since postmortem changes will make the accuracy and effectiveness of diagnostics questionable.
- Inability to collect the right tissues.
Keep the work area clean to avoid contamination. While veterinarians or on-farm personnel usually do not have a dedicated area for posting pigs, a clean work area with good lighting (like outside the barn on the gravel or grass) is still helpful.
Your veterinarian will follow a routine collection order by starting with systemic tissues such as the heart, lungs, liver, spleen, kidney and lymph nodes/tonsils. Samples of the small intestine and colon will be collected last to avoid fecal contamination. Postmortem kits can be a convenient way to organize the supplies needed and serve as a reminder of which tissues to collect.
After the organs have been removed, they should be individually packaged in whirl packs. If a clean surface is unavailable, each organ should be put directly into the whirl packs to avoid contamination.
It is important to collect enough of each organ to allow for multiple diagnostic tests. In general, a fist-sized piece should be adequate. With larger organs, such as the lung from larger pigs, there will be more volume of tissue than is needed. In this case, make sure to collect a sample of the abnormal-looking part of the lung — such as the part with pneumonic lesions — for lab analysis.
Culture swabs can be used to sample fluid from swollen joints or other locations.
Formalin-fixed tissues from each organ are collected so that the pathologist can look at these tissues under the microscope for characteristic lesions caused by specific disease processes. This is referred to as histopathology.
To prepare the fixed tissues, collect a thin slice of each organ (no more than 1 cm thick) and place it in a whirl pack, then add 10% formalin to “fix” or preserve these tissues. To adequately fix the tissue, at least a 3:1 ratio of formalin to tissue by volume is required.
It is especially important to make sure the whirl pack containing formalin is adequately sealed by holding the tabs at the top of the pack and “whirling” the bag around at least six times, then folding over the tabs.
- Not properly storing and shipping tissues.
After the pigs have been posted and the tissues processed, it is critical to refrigerate the sample packs until they are shipped to the lab to prevent additional decomposition.
Tissue samples should be driven directly to the diagnostic laboratory or shipped “next day.” Every effort should be made to maintain a cool temperature without freezing the tissues. Gel packs can be frozen and used to keep the package cool during shipment. Diagnostic labs typically provide foam coolers and cardboard shipping boxes for this purpose.
Tissues samples also must be sealed to prevent leakage and comply with shipping regulations. Packages that are leaking will not be delivered.
The whirl packs containing the samples from each pig are packaged together in a one-gal. zip-lock bag, which is then packaged in a larger zip-lock container along with others, if there are tissues from multiple pigs. This larger zip-lock bag is then put into the diagnostic lab box that is lined with a garbage bag.
- Not taking precautions to prevent injury or infection.
Some viral and bacterial diseases of swine are zoonotic (also having the potential to infect people). For this reason, it is important to take precautions by wearing latex gloves, boots and coveralls when posting pigs or handling tissues. Washing or showering after postmortem exams is also a good idea. Disinfectant wipes are an additional option for cleaning your hands and equipment where other options might not be available.
Use a sharp knife for the posting process. A sharp knife is much easier and safer to use than a dull knife, which forces the user to apply greater pressure to cut through tissues. A knife is obviously a potential cause of injury. When you combine a cut with infectious organisms, the risk can be compounded. Use common sense to avoid injury.
Posting pigs and processing tissues for laboratory diagnostics can seem intimidating at first, but with guidance from your veterinarian, this information can provide valuable information.
When mortality rate becomes a concern, it is important to quickly identify groups of high-risk pigs and identify the right pigs to post and collect samples for the laboratory. From there, it is just a matter of keeping things clean, and safely following a systematic approach to collect the right tissues, package them properly, and ship them off to the diagnostic laboratory.