The practice of using oral fluid collection to monitor for the presence of porcine reproductive and respiratory syndrome (PRRS) is gaining wide acceptance in the Midwest, says Gordon Spronk, DVM, Pipestone (MN) Veterinary Clinic & Pipestone System.

Data from Iowa, Minnesota and South Dakota diagnostic labs indicates that oral fluid sample submissions are gradually replacing serum samples.

Collection Procedures

In the Pipestone System, oral fluid sampling begins in farrowing using a single-strand, cotton rope. Ropes should remain in the crates for 15-20 minutes, until they become saturated with saliva. Half-inch ropes or smaller are best for the nursery and 5/8-in. ropes are recommended for finishing pigs, Spronk advises.

“One suggested protocol that has been successfully implemented in farrowing is to remove the crate dividers separating three farrowing crates to allow the piglets from all three litters to mix. Immediately place a training rope on the flooring of the
combined crates. Within a short period of time, some, if not all, litters of pigs will be attracted to the rope,” Spronk reported at the Iowa State Swine Diseases Conference for Swine Practitioners held in November in Ames, IA.

When the piglets have become accustomed to the training rope, remove it (because it is dirty or contaminated) and hang a new sample rope for oral fluids collection. “The sampling rope is distinctly different from the training rope because the training rope will be filled with feces and will get dirtier than the rope you want to extract fluid samples from,” he explains. Both are cotton ropes.

If young pigs aren’t attracted to the ropes, Spronk offers these tips to improve oral fluid collection:

• Vary the time of day when hanging ropes in crates. Morning generally works better than afternoon because pigs are more active earlier in the day.

• Add flavoring to the training rope. Apple juice or other flavors will attract pigs, but only use flavoring on the training rope. Flavoring helps collection in litters that are ill.

• Be sure that pigs can easily reach the rope. Ropes are often hung too low.

• Avoid removing the rope prematurely. Some technicians just aren’t patient enough, Spronk says.

• Do not throw in a rope and leave it overnight; that’s a common mistake.

• Do not use the training rope as the sample rope. Be sure technicians are trained to know the difference between the two.

• Sample older litters in farrowing; they are more aggressive and more attracted to the rope than younger litters.

• Train staff to check and submit only normal oral fluid samples; use the same scrutiny you would for submitting proper serum samples or nasal swabs. If the rope sample appears clear, there’s likely been an error in collection.

In the Pipestone System, oral fluid collection has been used for the last two years to gain some confidence in knowing the incidence of PRRS in the population and using the procedure to classify the herd status.

Sow farms are the key to PRRS status, so the first week of every month, four oral fluid samples are taken from the four farrowing rooms with the oldest pigs to evaluate status. Samples are submitted to the University of Minnesota Veterinary Diagnostic Laboratory, Iowa State University or South Dakota State University labs and evaluated by polymerase chain reaction (PCR) for PRRS virus and swine influenza virus.

“Our goal is to classify the herds and watch their progress over time to produce negative groups of pigs and maintain that status over a period of time,” Spronk comments.

Wean-to-finish sites are also monitored, with one nursery-age sample and two finishing-population samples collected randomly, also analyzed by PCR.

Future oral fluid sampling for the Pipestone System may be to switch to the enzyme-linked immunosorbent assay (ELISA) that has been validated by Iowa State, Spronk says.