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Managing PRRSV in sow farms in high dense areas

National Pork Board Sow farm (2).jpg
Investing in positive pressure filtration has been pivotal in lowering new virus introduction for Iowa Select Farms.

Overseeing 240,000 sows across Iowa, Pete Thomas has some experience managing porcine reproductive and respiratory syndrome in sow farms in high dense areas. In fact, the director of health services for Iowa Select Farms could probably set his watch to when farms are most likely to break.

"They always seem to break right in a very tight window in the fall or a very tight window in the spring," says Thomas. "I think last year we had a couple breaks, and they were within a week of each other in the spring, and then in the fall it was like a week before to a week after Thanksgiving and the weather was just perfect for virus movement."

Managing gilts
To combat new outbreaks, one of the areas Iowa Select Farms strives to work on is their gilt management program. All of their gilts get their core gilt vaccinations outside of PRRS, but then when it comes to a PRRS vaccine, all gilts will typically receive a modified live vaccine.

"We don't want our animals to be PRRS naive in Iowa, we just have too much disease pressure," Thomas says. "We can manage our way through the productivity and the losses of a PRRS outbreak better, we feel, if we have a vaccinated animal."

Gilts get vaccinated upon entry into the sow farm and then a couple times through the year, Thomas says.

The pork production system also tries to place gilt grow-outs in "low swine-dense areas."

"I use that term relatively, that'd be kind of the southern Iowa areas where we have our gilts that we grow out," Thomas says. "We still have gilts grow-outs that break with PRRS unfortunately, but we try to keep those animals away from most of our sow herds and most of our commercial grow finish, and also we do have other producers that have grow/finish in those areas but a lot lower swine density."

Thomas says the breeding gilt development units have been their safest locations.

"The majority of our sow farms, over half, would take a bred gilt into those farms so a gilt is somewhere around 10 weeks pregnant," Thomas says. "We breed those gilts off site, and they go to a safer location, the more isolated areas or they are in filtered facilities, and we do not do any routine live virus inoculation of our gilts."

Since naïve herds are impacted much more severely by PRRS outbreaks, the pork production system tries to keep their animals from being naïve.

Historically in Iowa, in the highest swine dense areas the PRRS break rate is 86%, which Thomas says occurs about every 14 months on average. While herd closures have extended since processing fluids started, Iowa Select has seen their closures average around 44 to 45 weeks, rather than 30 weeks.

"Once we complete that elimination, the odds that we don't find that wild type back in that sow farm I'd say within the next six to eight months is about 75 to 80% odds of true elimination," Thomas says. "When you think about that, when you have a herd that's going to break with PRRS every 14 months, it's going to take you the better part of the year for a closure and the success rate, the impact of that closure on parity structure and the reduced throughput doesn't make a lot of sense in our situation for those farms."

Instead Iowa Select's strategy is to keep the virus out through biosecurity and positive pressure filtration. Endemic farms are managed through vaccination, gilt introductions, and "mini" closures.

Dealing with endemic farms
On endemic farms, Iowa Select rarely attempts to eliminate the virus from farms where odds of long-term (two-plus years) run without new virus introduction is low. Instead, they conduct quarterly whole herd vaccinations and rotate with a couple products, to help get broad spectrum protection. They have also started using a killed vaccine. Thomas says so far reproductive loss has been minimal

"Occasionally we'll get a little blip but really don't have many problems reproductively," he says. "Especially if we're bringing open gilts into a farm, even with bred gilts, it can sometimes be a little bit problematic, but reproductive losses generally aren't very big."

Mini closures are put in place for 10 to 20 weeks at a time and are often combined with nasal virus exposure.

"We do that if a herd starts acting up or acting more unstable and so that's kind of what we would call a mini closure," Thomas says. "We're not trying to eliminate the virus but we're trying to get to the status where we're not finding it on processing fluids at least on a routine basis."

The biggest concern with the endemic farms is the lower born alive, Thomas says, with about 0.4 lower born alive and 1.5% higher mortality post weaning.

Keeping the virus out
From a biosecurity standpoint Thomas says Iowa Select Farms tries to focus on the main ways disease gets into the herd. To dispose of mortality at sow farms and gilt sites, they utilize rendering, incineration or rendering pick-up with a dedicated Iowa Select owned truck with a controlled route. The truck is washed, disinfected and baked daily.

For animal movements, much of Iowa Select's focus is placed on trailer sanitation. Trailers are washed, disinfected and baked. Transition rooms and areas are also in place.

For people entering the site, Iowa Select Farms has strict limitations and segregate staff that don't work between grow-finish and sow farms. Supplies coming in go through a UV chamber as well as a disinfection and drying room. One-off deliveries are limited.

Since animal testing is always a big risk, Iowa Select Farms executes a robust testing program through their internal PCR lab and animals are tested multiple times during the week moving occurs.

Finally, the pork production system uses a feed mitigant, not just for PRRS, but also for porcine epidemic diarrhea and foreign animal diseases.

Positive pressure filtration pays off
However, Thomas says positive pressure filtration is where Iowa Select has made the most investment over the last six years. Ten GDUs, nine new sow farms and 21 remodeled sow farms now have the system in place.

"We've been able to reduce our new virus introductions by over 4.5 times what they were so we can get long stretches of time," Thomas says. "We can help get these herd closures longer, herd closure eliminations to pay off."

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