You might as well accept the fact that controlling or eliminating disease from a swine herd is a never-ending battle. That doesn’t mean it’s not a responsible priority.
You have to be diligent in your disease-control and eradication efforts in order to keep up with a herd’s changing health status, says Paul Yeske, DVM.
“Even though we want herds to stay at a high-health level, history shows that health status changes over time,” says Yeske, with the Swine Vet Center, St. Peter, Minn.
He points out that disease-free production is “the goal that would allow producers to realize an animal’s full production potential.” However, disease-free doesn’t always have to mean pathogen-free. “The main goal for commercial pork production is to keep the pathogen level below the disease threshold,” he says.
Yeske cites eight eradication methods that can apply to today’s production systems — depending on the disease you are trying to eliminate. But even though disease eradication is the gold standard, it’s not always attainable.
This is the most straightforward disease-eradication method. It offers the opportunity to address multiple diseases at once.
Depopulation/repopulation has been successful for diseases such as pseudorabies, porcine reproductive and respiratory syndrome, atrophic rhinitis, Actinobacillus pleuropneumonia, swine dysentery, mange and other swine diseases, he notes.
Besides the disease-eradication benefits, depopulation/-repopulation provides an opportunity to upgrade genetics or restructure a herd’s parity distribution. But, it can be a challenge to find enough disease-free stock to repopulate the herd. There’s also always the possibility that the “new” herd will re-break with a disease, despite stringent biosecurity measures.
Yeske points out that Swine Vet Center veterinarians have successfully used the following procedures to depopulate and repopulate their clients’ swineherds.
Detailed site clean up: This includes washing the entire facility and removing all organic matter such as feed, manure and saliva. All items that cannot be thoroughly washed are removed and replaced.
Maintain a specified downtime: This means no pigs on the site. The downtime is determined by the failure cost within the system, and the specific pathogens you are attempting to eradicate. Four weeks is the most common time frame, but some successful programs have shut down for as little as a one week.
Disinfect the entire site: Everything in the facility must be completely disinfected and dried.
You may have to do things like use a leaf blower or air compressor to blow water from troughs or water cups. Inspect and repair leaking water lines. Remove all equipment possible from the building and dry it in the sun.
Using two different types of disinfectants to conduct a double disinfection is wise.
Fumigate the facility: This should be done two to three days prior to new pigs arriving at the facility.
Enforce strict biosecurity: Monitor and regulate people, including employees, visitors and service people that come and go from the facility site. Monitor and regulate animal movements. This includes creating trucking protocols for animal movements within a system, as well as installing internal truck washes. Ensure that trucks used internally never leave the system.
Properly remove and compost or incinerate dead animals. Quarantine incoming supplies, including medications and vaccines for a time period; disinfect what you can. Implement strict animal-isolation protocols and test all groups of new pigs prior to entering the herd. Maintain pest-control programs for rodents, birds and insects.
2. Test and removal
This option requires that animals exposed to a specific disease pathogen are no longer shedding the organism. Test and removal proved to be an effective way to eradicate pseudorabies.
“With PRV there was an effective vaccine that developed immunity and reduced shedding in affected animals, as well as providing markers that allowed differentiating infected animals from vaccinated animals,” says Yeske.
Test and removal has been used in some attempts to eradicate PRRS, “but it has been difficult to predict the outcome. Most herds that have tried this method have been small, with only one PRRS virus strain present…it was usually done in combination with a herd closure, and after negative animals replaced others.” He notes that except for seedstock suppliers and boar studs, this procedure has not been widely used to address PRRS. That’s because the time requirement is long and there is a high failure rate.
“The herd must first stabilize, then wait 6 to 12 months for titers to drop before testing can begin. Then there’s always been concern as to whether a herd is truly negative until all infected animals are removed,” notes Yeske. “Using direct virus exposure does help ensure that all animals were infected, allowing the herd to stabilize quicker, and thus making the procedure a little faster.”
3. Swiss depopulation
This method was developed to eradicate Mycoplasmal pneumonia, says Yeske. “Some Mycoplasma experts argue that the method doesn’t actually eradicate the disease. Rather it gets it low enough so that it doesn’t cause clinical disease.”
However, several European countries (such as Switzerland and Finland) have used this method with success. The premise is to use the pig’s immune system to fight off disease and prevent having animals that can keep infection cycling in the herd.
Swiss depopulation protocols require that you don’t bring any disease-positive animals that are younger than 10 months into a herd, explains Yeske. Such animals have been previously infected at a young age so they’ve had time to develop immunity and stop virus shedding.
The entire population should be medicated for two weeks to kill any Mycoplasma present in the herd. Farrowing is stopped for a two-week period to avoid having piglets that could spread the organism. After that, the herd can use disease-negative replacement animals and should remain negative. Yeske adds that “this method requires coordination so that farrowing ends, medication is underway and strict biosecurity is met.”
Work is underway to determine if this method can be successful without the farrowing break, but it’s too early to predict.
While this method has been successful in some cases, it’s not foolproof and requires further evaluation, says Yeske.
4. Medication programs
Medication programs have been successful for some of the bacterial diseases such as swine dysentery, Yeske notes. To be successful it requires you to treat the entire herd at once. It also requires strict site clean up, sanitation and rodent control measures.
“This is done using several different antibiotics for a two-week period,” he notes. Mange is another example of using a whole-herd medication program to eradicate a disease, he adds.
5. Segregated early weaning
Yeske believes that segregated early weaning has reshaped pork production; that it has allowed commercial producers to adapt multiple-site technology.
“Multi-site production that’s all in/all out by site essentially allows for a site to be depopulate and repopulated with every turn of pigs,” he notes. The principle is to use the herd’s immune status to protect the piglets, wean them at an early age and remove them from the site while they have high maternal immunity levels and before they can be infected.
Weaning age depends on the pathogens to be eradicated, as well as the maternal antibodies’ rate of decay. “In some programs to eradicate bacterial diseases, antibiotic treatment is applied to the sows and piglets to put in one more barrier to infection prior to moving piglets off-site,” says Yeske.
He notes that method has been effective to eradicate PRV, atrophic rhinitis and Actinobacillus pleuropneumonia. It’s been tried for PRRS eradication, but hasn’t always been successful because the virus was circulating in the herd’s population.
6. Closing a herd
This practice halts gilt-replacement introductions into a sow herd, allowing the herd’s immunity to stabilize and stop shedding organisms because the pathogen no longer has a susceptible population in which to circulate.
When herd closure has been used to try to eradicate PRRS, the downtime has required 200 days following the last recovered animal. “The challenging part is knowing when the last animal is exposed,” Yeske notes. Using direct-virus exposure can help ensure that all animals are exposed. The next biggest problem is maintaining the breeding herd inventory during that period in order to keep the system full.
“Using an off-site breeding project is one solution,” he says. “This involves maintaining a disease-negative gilt population at another site where they are bred and brought into the herd after it’s closed, but before the gilts are due to farrow.” This can dramatically reduce the erosion of the sow herd inventory, but there are always additional costs and risks when another site is involved.
Herd closure also may be effective for other diseases, but so far it’s mainly been used in attempts to eradicate PRRS.
7. Direct-virus exposure
The principle here is to expose all animals in a herd to a specific pathogen, but not provide an avenue for it to maintain itself within the population.
“This approach is probably best suited to viral diseases that don’t develop chronic shedders,” says Yeske. “The classic example has been TGE eradication from herds.” In that case, all animals are infected with the virus strain from the farm. It has been successful in both acutely infected herds as well as chronically infected herds.
Direct-virus exposure is being attempted in PRRS-eradication programs to quickly generate negative pigs for downstream flows. “It may be effective in herd eradication especially if used in combination with herd closure before rolling over the positive population with PRRS-negative replacements,” says Yeske.
This can be used to eradicate some diseases if the vaccine can control the pathogen and reduce its shedding within the herd. PRV eradication is an example of a vaccine that helped eliminate a virus from the national swineherd.
Of course there’s no such thing as 100 percent success, 100 percent of the time. It all depends on the disease, the production system and the personal goals and tolerances of the herd’s owner and veterinarian. Some pork production systems use a combination of disease eradication options.
Any and all options have to be fit to the unique aspects of each production system, says Yeske.