Sampling Oral and Processing Fluids to Identify Disease in Pigs

 

Monitoring your herd for diseases has been simplified by new tests using oral and processing fluids. These sampling techniques are inexpensive, easy to do and can be applied to individual pigs (as a diagnostic) or pens/litters (for herd surveillance).

 

Successful farmers know the importance of protecting their herds from disease. They know that preventing disease by purchasing healthy animals, using pig flow, appropriate nutrition, vaccines and practicing sound biosecurity is more cost-effective than treatment.  However, keeping animals disease-free is not always possible. Recent guidelines restricting use of feed-grade antibiotics have added to this challenge, as have concerns over the potential for outbreak of a foreign animal disease such as African Swine Fever. In this context, the next line of defense against disease transfer is early detection before infection spreads to pigs within the farm or other farms. 

 

Traditional methods for disease detection required collection of blood or other tissues was stressful for animals and required considerable technical skill, time and expense. Fortunately, new methods have been introduced that allow detection of several important diseases, at the herd or individual pig level, by sampling oral fluids (collected from the mouth) or processing fluids (fluids derived from testicles or docked tails).  Both oral and processing fluids are well suited for identifying disease at an earlier time. Both methods require little time or skill and involve no additional (or minimal/stress-free) handling, so animal performance is not adversely affected.

 

 

Oral fluid consists of a mixture of saliva and oral mucosal transudate (antibodies and other proteins that enter the mouth by crossing blood capillaries lining the mucosa). Chewing stimulates oral fluids production. These fluids, according to the research of oral-fluid samples, can be collected when pigs chew on a cotton rope suspended at pig shoulder height in the pen, typically for 20-30 min, and is processed using a simple 4-step procedure. This approach is well suited for conducting surveillance in barns whereby the ropes are a novelty for most of the pigs in the pen and oral fluids are a pooled sample of multiple pigs. However, pigs raised outside, on straw, or in smaller groups may have other distractions and may not be sufficiently curious about suspended ropes. For these pigs there are a few other options: a) train the pigs to chew using attractants such as smeared peanut butter on the rope 2-3 days ahead of sampling, b) use segments of a cotton mop (which pigs typically find more interesting than a single rope) or, for an individual pig sample, c) fashion a cotton rope into a “harness” that passes through the back of the pig’s mouth and loops behind the ears (Fig. 2).  Oral fluids can be used either for individual pig sampling or to reflect the pen infection rate. Swine diseases for which oral or processing fluid-based assays have been developed include PRRS, SIV-A, PCV-2, M.hyo, stomach worm and others (Table 1).

 

 

Processing fluid provides another simple and efficient method of sampling for disease. Rather than discarding tissues during processing (castration and tail docking), the testicles and tails from litter-mates are placed in a clean bucket and the fluids are filtered through cheesecloth into a plastic bag. The contents are transferred into a sterile tube and shipped on ice to a veterinary diagnostic lab. Typically, the process is repeated for 5-6 litters within a barn. Processing fluids are an important sample to be assayed to determine disease in piglets early and help to identify if infection is in the sow barns, before the pigs are weaned. Processing fluid testing has detected PRRS, PCV-2 and other diseases with high reliability. The major disadvantage of using processing fluid for disease surveillance, relative to oral fluid, is that it considers only the eonate and can be collected at only a single time point (i.e., at processing) per animal.

 

 

 

*This list is incomplete and expanding steadily for oral fluid and processing fluid diagnostics. Tests are PCR or ELISA based.

 

**In the configuration used at ISU, a variation on egg/larval stage detection is used.

 

***These assays are currently in experimental stages and not fully validated, but will typically be conducted upon request.

 

Role of your veterinarian.  Your veterinarian will provide advice regarding which tests to conduct (diseases to test for, number of litters to test and whether PCR or ELISA should be used).  Samples you collect are typically shipped by your veterinarian to a veterinary diagnostic laboratory for assays (PCR or ELISA) that determine either the presence of the bacteria or virus or confirmation that the animal has been exposed (Table 1). Test results are typically available directly to your veterinarian within 2-3 days for follow-up.

 

Trends in oral and processing fluids diagnostics.  What is next for oral and processing fluids testing?  Based on recent reports, such as the Population- based diagnostics report, oral fluid and processing fluid are rapidly becoming the most important tools for detecting disease in pigs, already outpacing blood sample testing. This is probably driven in part by the ease of collection and relatively low cost provided by these forms of diagnostic testing.  Leveraging the full diagnostic power of oral fluid and processing fluid testing will require additional research to determine the optimal number of animals to sample, frequency of sampling, and how to design sampling protocols that are random yet also account for spatial patterns that typically characterize spread of disease within a barn.