How to manage herd closure for PRRS elimination

Herd closures to eliminate porcine reproductive and respiratory syndrome (PRRS) are on the increase due in part to the virulent variant identified as PRRS 1-4-4 L1C.

“PRRS 1-4-4 L1C has hit people hard,” reported Paul Yeske, DVM, Swine Vet Center in St. Peter, Minnesota. “The elimination process for this variant is what we’ve done for all PRRS viruses, and the program has been very successful at getting the herd to make PRRS-negative pigs.”

Yeske offered suggestions for a successful herd closure to eliminate PRRS from a farm.

Prepare for herd closure

The first step is increasing gilt inventory to cover the full closure time, which typically runs 210 to 240 days, according to Yeske.

“If there’s an on-site gilt developer where the farm is getting the gilts as Isoweans, they already have 6 months of gilts and only need to increase capacity for a couple months,” he said. If the farm has no on-site gilt development, they must either find another site to hold these animals or be able to fill the space available and live with the current inventory.

Just prior to closure, Yeske recommended implementing a feedback program that’s given to all sows and gilts to provide scour control for 6 to 8 months of the closure. “A lesson learned from PED (porcine epidemic diarrhea) was that we can help ourselves on scour control by doing a whole-herd feedback at the beginning of a herd closure,” he said.

Closure begins

Herd closure begins when sows are exposed with serum collected from the farm site. This occurs after the sow herd has recovered from the initial break and are eating and feeling good again. Some farms even wait until all replacements are on site.

He suggested following up 3 weeks later with a statistical sampling around the site to confirm the herd is positive. Make sure to obtain tests from all barns to ensure all animals are positive going forward.

“The injections start the clock ticking for 240 days and maybe longer, depending on how testing goes,” Yeske said. “Essentially, we wait for time to allow immunity to develop and shedding from sows to decrease.

“The theory is the virus will shed for a period of time, and the immune system will clear the virus from the sows,” he explained. “Since there are no animals in the herd that can be infected, theoretically the virus should die out on the farm, allowing for negative replacements to enter and not become infected.”

Throughout the herd closure, Yeske said the farm should focus on cleaning and disinfecting rooms, hallways, loadouts and any place weaned pigs move. Also, movement between litters should be minimized, and staff should be diligent about changing boots and coveralls when going back to handling young pigs. They should always work from youngest to oldest pigs, and change and clean up before going back to younger pigs.

Testing regimens

After 10 to 12 weeks of closure, collecting and testing piglet processing fluids begins, which will indicate the level of viremia in piglets. “Are we still positive or are we going negative?” he said. “We watch the Ct (cycle threshold) values and hope to see them go up. A lower number means more virus in the sample.”

Yeske recommended using processing fluids because samples are relatively easy to obtain, and it is less expensive than other testing methods. Plus, it essentially tests all piglets in a pooled sample, he added. Most farms pool a week’s worth of samples to reduce cost, yet still monitor to see if the herd is progressing.

When processing fluids start testing PRRS-negative, then piglets should be tested at weaning to see if they have remained negative through lactation. At this point, processing-fluid samples should be tested by room or day to help isolate the positive locations.

“Before weaning, most do blood testing, but you can use family oral fluids,” Yeske said. “With family oral fluids, hang the rope so the sow can chew on it first, and the piglets will chew on it too. Some litters respond better to family oral fluids than others, which is why most will use blood samples.

“The other option is to blood test the poorest-quality pigs, 30 to 60 a week or month, to establish if pigs are negative at weaning,” he added.

When to open herd

Depending on the farm, some use 60 days of negative tests at weaning, and others use 90 days of negative tests before ending the closure, according to Yeske.

“What we’ve seen is 210 days is the sweet spot for herd closures,” he said. “We tried 180 days and didn’t have good success. If you use 210 days, you have higher confidence that the herd is ready to take PRRS-negative gilts.

“And if you don’t get the piglets testing negative at 210 days, then we just wait. That’s when some people go to 240 days or longer. Remember, time is your friend in elimination programs versus ending the closure too soon.”

Closure ends

Once the closure is finished, the final step is repopulating. If a genetic supplier for a farm with an on-site gilt developer can provide a staged population, Yeske recommended refilling the gilt developer that way.

If only weaned pigs are available from the supplier to repopulate the herd, the farm will need a clean place to raise clean animals. “That’s a potential limitation, and you must think about that going into an elimination,” he said.

“Overall, the process of PRRS elimination is relatively inexpensive. And it’s been able to push the field virus out of herds,” Yeske added. “Some farms in pig-dense areas will maintain a vaccination status. They will be negative to the field virus but have a PRRS vaccine to have some herd immunity in case of a new virus exposure.”

 

 

How to avoid winter ventilation pitfalls

During winter, swine facilities usually operate at minimum-ventilation rates. But if those rates aren’t correct, high humidity and excess gases will build up leading to increased disease and reduced growth rates, reported Sam Holst, DVM, Swine Vet Center, St. Peter, Minnesota.

“A good understanding of basic ventilation concepts and some routine monitoring to make sure everything is working properly will help set up a barn environment to optimize health and performance while also keeping utility costs in check,” he said. “A lot of ventilation mistakes result from efforts to try to save propane or other utility costs.”

Holst offered several tactics to avoid common winter ventilation mistakes that increase costs.

Calculate minimum ventilation

A big mistake that increases costs and reduces pig performance is an incorrect minimum-ventilation rate.

“Minimum ventilation is the amount of fresh air needed to be brought into the barn to help control humidity and gases like carbon dioxide and ammonia,” Holst explained.

“It’s important to get this correct because over-ventilating will waste propane and electricity leading to inflated utility costs,” he said. “On the flip side, if we under-ventilate, we’ll produce an environment that’s detrimental to health and performance.”

Minimum-ventilation rates should be calculated based on the number of pigs in the room and size of the fans on stage one. Use the following reference charts to help determine the minimum rates. Reference charts for required maximum cubic feet per minute (CFM) per pig and fan CFM output (Figure 1) and  (Figure 2) are helpful for these calculations. (Located at end of article.)

“It’s worth the time and effort to calculate the minimum-speed setting for stage one rather than use an arbitrary setting,” Holst added.

Set heater correctly

During the winter, heater and furnace use increase greatly. Holst stressed making sure the heater is set correctly to achieve consistent room temperature and limit propane waste. He’s seen propane use drop by several gallons per heater per day when settings were corrected.

One costly mistake is setting the heater shutoff temperature too close to the set-point temperature. Room temperature rises even after the furnace shuts off as it takes some time for the heated air to circulate and the probes in the building to detect the increase in room temperature. If the heater is programmed to shut off too close to set point, the room temperature will rise above the set point causing minimum-ventilation fans to speed up and exhaust heated air – essentially blowing recently burned propane right out of the building.

“A good way to finetune furnace settings is to make note of the current settings and watch the room temperature as it cycles through a heater on-and-off run,” Holst explained. “Ideally, once the heater shuts off, the room temperature should rise to just below set point without going over. If the temperature rises above set point, then adjust the heater setting so it shuts off further below set point. In most cases this will be 1.5˚F to 2.0˚F below set point.”

Check temperature probes, fans

All the temperature data fed into the controller to determine ventilation settings comes from temperature probes located in the facilities. If the probes are not functioning correctly, are placed in incorrect locations or are at the wrong  heights, information fed into the controller is inaccurate.

“If that happens, the result is an unfavorable barn environment,” Holst said.

Also, make sure fans are clean and not covered with  debris and dust. Just 1/8 inch of dust will reduce fan efficiency by 40%, he added.

Wrap curtains in plastic

“It can be beneficial to cover curtains with bubble wrap or plastic in the winter to help reduce drafts and heat loss,” Holst said.

His recommendation is to fully cover curtains on the north side of buildings with bubble wrap or plastic. On the south side, cover the curtains up to one foot from where it opens at the top so the curtains can be opened during a warm day.

Following these recommendations for winter ventilation should help keep utility costs in check and provide a healthy environment for pig growth through cold weather, he added.

 

Figure 1.

 

Figure 2.

Mycoplasma hyopneumoniae elimination becomes possible

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Over the past two decades, the swine industry learned how to eliminate Mycoplasma hyopneumoniae (Mhp) from herds without depopulation/repopulation, according to Paul Yeske, DVM, Swine Vet Center, St. Peter, Minnesota. Yeske has been at the forefront of the efforts to eliminate the respiratory disease for clients.

The move to eliminate Mhp from herds has “really picked up momentum in the last 4 to 5 years,” Yeske added in an interview with Pig Health Today. In fact, efforts are underway to work towards areas or regions in Minnesota that are Mhp-free, with the end goal being the elimination of the disease from the state.

Why elimination?

When the industry moved toward high-health status sow herds, instability increased when Mhp-negative replacement animals entered positive herds and became infected just before farrowing, Yeske explained. Maintaining an Mhp-stable herd was a lot of work because the organism is very slow and takes a long time to infect animals and you must be deliberate in every step of the process. It also takes a long time for Mhp to clear from animals – up to 240 days. Gilt replacements need to be exposed by 80 days of age so they are not shedding the Mhp when they farrow.

As a result, many producers decided to eliminate it from their systems. Yeske noted that once a system has a good gilt-stabilization program, the herd is also set up well to go on to an elimination program.

“The herds we stocked that were negative from the beginning showed us the advantages of negative production,” he explained. “If you look at the literature, [the cost of Mhp] is anywhere from $2 to $10 a pig, and the average probably being in that $5 range. We know there’s a significant cost and a significant return.

“If we do a long-term closure, we’re talking about somewhere in that 3- to 4-month payback,” he continued. “If we do a heavy medication program and no closure, we’re talking about an 11- to 12-month payback.”

In addition, eliminating Mhp takes away the “add-on effects” when a herd experiences other infections like influenza and porcine reproductive and respiratory syndrome (PRRS) which can be even more costly.

“Producers have taken the approach —  ‘let’s take one off the table because we can’,” he said.

Statewide elimination efforts

Leading the work to eliminate Mhp from Minnesota is Maria Pieters, DVM, University of Minnesota. Yeske said the plan is in its early days but hopefully they’ll be able to get more herds involved and help reduce the potential for lateral risks of Mycoplasma spread.

“But it’s like any other voluntary program…there’s always going to be some period of time for adaption,” he said.

He doesn’t expect that in five years Mhp will be eliminated, but “hopefully at some point, I can still come back to the Leman Conference and say, ‘We used to have Mycoplasma‘.”