Stabilizing PRRS-positive herds through closure

​​​​​​​Getting field strains out of herds now lessens blow on wean-to-finish performance.

Ann Hess, Content Director

August 1, 2022

7 Min Read
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National Pork Board

When it comes to porcine reproductive and respiratory syndrome herd stabilization, Paul Yeske says producers have three options — allow the herd to remain positive, eliminate the field strain or depopulation/repopulation.

"I think we're more likely to see those viruses continue to change, at least in my experience over the years that's what I've seen, and that's where these new strains we're seeing with more persistent wean-to-finish problems," says Yeske. "One of the things that surprised me the most here recently is the number of depopulations/repopulations we've been involved with. I remember back in the early 90s doing lots of these for lots of diseases and here we are back at it again."

During a recent PRRSV Management Workshop in Iowa, the senior member of the veterinary team at Swine Vet Center, shared his tips to succeed on a herd closure as well as the status of the new PRRS 1-4-4 L1C variant. He says so far, the virus presents itself similar to other viruses. There's a rough two to four weeks, then the sows return to normal and there have been very low live born due to a high percentage of mummies.

"Some farms have gone longer but we've had farms that clean up in the 32-week time frame," Yeske says. "The first thing you do is stabilize the herd and get everybody exposed and so again you want to encourage the virus to move around. We let the aborts, off feeds out and let them move through the barn to try and get some exposure that way."

Yeske says one of his clients came up with the idea after dealing with porcine epidemic diarrhea, gaining six to eight months of scour control from the whole herd closure

"By doing that whole herd feedback you kind of get that magic window like we did at PEDV, where you get good scour control while you're going through the closure," Yeske says.

If a producer chooses to do a serum exposure as well, whether that is one or two dose injections, will depend on the individual farm preferences, Yeske says.

When it comes to maintaining the breeding target during the closure, Yeske says "the golden rule of all pig farms is you got to make breeding target no matter what."

"You're going to close the herd and we want to maintain inventory so the farms that have the on-site GDUs (gilt development units) certainly have the easiest opportunity to do this," Yeske says. "You've already got the space in the system."

The biggest challenge will be the two months of the gilts needed for the closure won't be born yet.

"That means you got to take more of the younger ones, that you can bring and increase that inventory," Yeske says. "One of the things we've done with that is, as we get to that big population of animals because we've got them there, to get the numbers, is to go ahead and breed those animals. We skip our P1s (first-parity) and our P2s (second-parity) to get those animals pushed further out and to not have too big of groups but be able to maintain that inventory."

For off-site GDUs, Yeske cautions if the production system decides to expose, that it is not in an isolated area that's clean.

"Because you don't want to take a bad field virus up into a clean area," Yeske says. "You don't want to do it where you are going to get a different virus into that finishing site so it makes it harder and harder to do these off-site gilt exposures and quite frankly, we've gone away from them from where we once would have been."

For off-site breeding projects where the animals are left unexposed, Yeske says this method works best for herds that are getting select weights and adding additional inventory is difficult. The only way the sows leave the farm is if they got a high-volume discharge, if they abort, if they have lameness concerns or mortalities. Otherwise, they stay in the herd until closure is completed until off site breeding can begin.

"Oftentimes managers struggle with this, and they'll cull too many animals and then they wonder where the inventory went and so maintaining inventory becomes one of the key components if you're going to maintain that breeding target through the closure," Yeske says.

If a producer is going to start an offsite breeding project, it needs to be within week 17 of closure and it must be on track for the herd to be negative at 32 weeks. However, the veterinarian says producers should wait for diagnostics to show the trend is headed in the right direction before starting a breeding project.

While McRebel (Management Changes to Reduce Exposure to Bacteria to Eliminate Losses from PRRS) is a good tool, Yeske says "it's kind of a get out of jail free card and sometimes I think it's been overused by farms."

"It's a license to hide pre-weaning mortality in the name of PRRS control," Yeske says. "It's an important tool once we've gotten to negative processing fluids but if we start it too early, we just end up with more mortality."

For diagnostic monitoring the Swine Vet Center takes processing fluids on piglets at day 3-7, blood samples and family oral fluids from due to wean piglets, and even tongue tips from mortalities and stillborns.

"If you're struggling and you can't get those due to wean pigs negative, but you got negative processing fluids, the early weaning down to that 10-day age range for anywhere from three to six weeks has helped us build that extra time for clean and disinfection and get some of that population that's shedding off the site," Yeske says.

How do you decide that the gestation herd is ready for a project like this? Diagnostics are key, Yeske says. Aborted sows must be tested the day of abortion and moved to an isolated area as soon as possible. Diagnostics also must be taken on piglets at birth, oral fluids from sows, and tongue tips from stillborns and day-old piglets.

"I think this is one place where the tongue tips may make sense in doing that in stillborns because there's no way that pig got contaminated in the environment, but it's an opportunity for us to look at that and see what’s going on in gestation," Yeske says.

As for production records, Yeske references 10 different farms Swine Vet Center worked with, all with 1-4-4 L1C and a very similar genetic pattern. However, looking at farrowing rates, not all farms were affected the same. The same holds true with pre-weaning mortality.

"They all have issues, but some are much worse than others and yes, they do get to 100% and we see some of the farms that gave us trouble down there into that 25-to-30-week range giving us a hump in the production record, so I think it only helps to give you another look at the herd's status besides the diagnostic data," Yeske says. "When you look at the pigs weaned per mated female, again that's part of why you see people doing some of the things they're doing (depopulation and repopulation), is just because of the long-term impact on the pigs for mated female going out the door."

As for a cost comparison on PRRS 1-4-4 LIC elimination control procedures, Yeske says it takes about six months to pay off depopulation/repopulation if you can do an off-site breeding project, nine months if you dump and start over.

With this strain's ability to live longer in the environment, Yeske says it is critical producers are practicing bio-exclusion and biocontainment at every site.

"I think the L1C will continue to be a prevalent virus at least for a while," Yeske says. "We can get the closures done in 32 weeks. More people are going to the depopulation/repopulation, but again I think we want to get these field strains out of these herds because we know the cost of the wean-to-finish performance is just too high to live with and we can get it done, we just have to pay attention to the details."

About the Author(s)

Ann Hess

Content Director, National Hog Farmer

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