A second, more subtle break occurred one year ago this November, again at the home sow farm, but it missed the nearby sow farm. Farrowing and weaning averages the last six months (to July 2011) bear out the differences in performance between the home farm that still deals with the PRRS virus and the nearby sow farm that consulting swine veterinarian Darwin Reicks says hasn’t had PRRS for over a year.

Joe Vansickle, Senior Editor

November 10, 2011

7 Min Read
Striking Back at PRRS

Lantz Enterprises’ farm manager Doug Siebenahler will never forget the PRRS outbreak of 2007. Two strains of porcine reproductive and respiratory syndrome (PRRS) struck with a vengeance.

When it hit, the 1,250-sow home farm was negative and naïve for the virus. “It just clobbered us,” he recalls. There were four months when farrowing rate was just 65%, about 200 sows aborted, and they had countless growing pig issues. The virus spread from one sow farm to another Lantz sow farm just a mile away, with a much less severe strain of PRRS, Siebenahler explains.

PRRS Strikes Again

A second, more subtle break occurred one year ago this November, again at the home sow farm, but it missed the nearby sow farm. Farrowing and weaning averages the last six months (to July 2011) bear out the differences in performance between the home farm that still deals with the PRRS virus and the nearby sow farm that consulting swine veterinarian Darwin Reicks says hasn’t had PRRS for over a year.

The “clean” farm has reached an average of 30.2 pigs/sow/year (p/s/y) year-to-date, compared to the PRRS-positive sow farm average of 26.5 p/s/y year-to-date, which is still quite respectable, Reicks notes. The latter farm also dealt with a recent bout of influenza and an ileitis outbreak, which may have been compounded by the PRRS status of the herd.

“We are happy with our production results,” Siebenahler says, “but the PRRS blip on the home sow farm probably cost us thousands of pigs in lost production.”

The sow farms represent two very different cases of PRRS in their severity, but they are both lasting examples of why living with the virus is not an option for the pork industry, says Reicks, Swine Vet Center at St. Peter, MN.

Change in Control Efforts

“I think for quite a long time, the Lantz Enterprises’ strategy was to make the sow farms truly negative. We tried to eradicate PRRS with serum injections (using a strain of the virus found on the farm) and herd closure, and then we were able to take the farms back negative,” Reicks says.

But he believes the increase in hog density in the area, in part from building finishing barns for manure contracts, led to the explosive PRRS break in late 2007.

“Because there were quite a bit of clinical signs and losses associated with that break, the strategy moving forward was not to necessarily take both farms completely negative, but rather to expose the gilts in the off-site gilt developer to the strain that was on the farms and to the vaccine strain (Boehringer Ingelheim Vetmedica, Inc. PRRS ATP vaccine), then bring the animals into the sow farm as negative but previously exposed to both the field and the vaccine virus strains,” he explains.

Just over a year ago, it was decided to forego future inclusion of field virus in control efforts (serum injection), and instead focus on using just the modified-live-virus PRRS ATP vaccine. Their program is to vaccinate incoming gilts twice in the off-site gilt developer unit (GDU), he says. The GDU is located 10 miles from the home sow farm in an area isolated from pigs, in a rented barn that holds 240 head.

“We have had to do some things differently there since we do our own internal multiplying,” Siebenahler explains. “Through this PRRS control period, we had to quit making our own gilts for a while, so we had to buy some gilts from PIC. We have been getting gilts at various ages to stock our production system. As soon as we get them in, we vaccinate and wait 2-3 weeks to vaccinate them again.”

The idea behind this new program is that the gilts will go negative, clearing the vaccine virus, before they are ever introduced into the sow herd, he says.

To ensure that gilts are not carrying the PRRS virus, gilts are blood tested before they go into the sow unit, Siebenahler adds. If a gilt turns up positive, the serum sample will be sequenced to make sure that it is the same strain as the vaccine strain. The gilts will be given a little more time in the GDU to clear the virus before being moved to the sow unit. So far, the only strain of PRRS identified in this new program has been the vaccine strain.

“To clarify, it is not really titers that we are looking at; it is whether gilts are positive or negative for PRRS,” Reicks says. “So far, gilts are only positive for the vaccine strain that we are trying to give them.” The goal is to have all the animals’ serum come back polymerase chain reaction (PCR) negative but ELISA positive.

The PCR test is used to identify whether the animal is infected with the actual virus. The ELISA or enzyme-linked immunosorbent assay indicates whether an animal shows evidence of previous exposure to the virus.

“We want the breeding herd to have been previously exposed, so if there is another exposure in the sow herd, we don’t have totally naïve animals that have never seen PRRS virus their whole life. With the memory cells of the virus, there is cell-mediated immunity to respond quicker to a challenge,” Reicks points out. In doing so, the farm hopes to avoid the big losses incurred in the 2007 outbreak.

Performance Enhancements

The sow performance the last six months is the best Lantz Enterprises has ever experienced, Siebenahler says. Granted, the efforts to control PRRS are reaping rewards. But other management enhancements are also helping advance production, including:


  • Two years ago, sow herd size was reduced from 1,250 to 1,100, and the operation was converted from farrow-to-wean to farrow-to-finish, utilizing contract growers and one owned barn to finish pigs out to 265 lb., Siebenahler says. A 2,400-head, wean-to-finish barn is also being built.

“Lowering the size of our sow herd has given us the opportunity to produce about the same number of pigs with less work and less stress on the crew,” he says. Fewer sows give staff time to provide more attention to detail, treating any animal that is sick right away.


  • Weaning age was adjusted up from 17 to 21 days of age.


  • Skip heat of more sows and breed back 21 days later on the next heat period. “We skip heat on Parity 1 sows that are underconditioned or that didn’t eat well in farrowing, and sows that are in poor condition,” Siebenahler explains.


  • Blood testing the sow herd every two weeks and testing gilts prior to joining the sow herd are critical parts of PRRS monitoring. “It has sure added to our costs, but it is information that is needed so we can stop pig movements in time if something doesn’t look right,” Siebenahler says.

Biosecurity Enhancements

Biosecurity was always maintained at a fairly high level, but the explosive PRRS break in 2007 led to tighter control of people traffic and improvements in trailer biosecurity, including washing weaned pig and cull sow trailers off-site.

Gilt barn biosecurity was ramped up so that gilts could be blood tested before they are moved into the sow herd. “We used to bring gilts in without testing them. It is just another challenge that PRRS has brought us. If you don’t test, you are going to have another costly blowout,” Siebenahler says.

Sow units are shower-in, shower-out and grow-finish units rely on physical barriers, such as changing boots and coveralls, washing hands and using sanitizer bottles.
“If people don’t do biosecurity right, then there are so many other things that probably aren’t getting done right also, because it sets up the mindset for the whole animal health thing, whether it is PRRS or another challenge,” Siebenahler emphasizes.

Grow-Finish Problems

This is only the second year that Lantz Enterprises has finished a portion of their pig production, and Siebenahler says it is tough to put a price on PRRS-related finishing costs. But groups of chronically affected pigs do show up, taking away from the “percent prime” sold to market. “We figure we lose 3% prime because of flare-ups in the grow-finish area,” he notes. Those pigs end up being sold to a cull market.

To retain the value of negative pigs from the PRRS-clean sow farm, weaned pig flows are split so groups are not contaminated, complicating pig flows, Siebenahler says.

A proactive feed medication program provides broad-spectrum control over other grow-finish health issues, including Actinobacillus suis, Mycoplasma pneumonia and a range of other issues, Reicks says.


A second GDU is planned as insurance, in case the first gilt developer becomes infected with PRRS.
Some thought is being given to installing air filtration systems for the two sow farms, after PRRS is “walked off the home sow farm,” Reicks says.

Granted, that is an expensive investment, he says. But evidence suggests area spread of PRRS in southern Minnesota is on the rise, which means reinfection by aerosol transmission is the biggest threat to PRRS freedom.

About the Author(s)

Joe Vansickle

Senior Editor

Joe, a native of Indiana, is a graduate of the University of St. Thomas in St. Paul, MN, with a bachelor’s degree in journalism. He worked on daily newspapers in Albert Lea, MN and Fairmont, MN, before joining the staff of National Hog Farmer in 1977. Joe specializes in animal health issues, federal regulations, environmental concerns, food safety and writing about the swine veterinary community. Joe has won several writing awards from the Livestock Publications Council. In 2002, he earned the Master Writer Program Award from the American Agricultural Editors’ Association.

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