Historically, PRRS research has been primarily focused on controlling PRRS virus in sow herds. The result has been development of protocols for acclimatisation, care closure and biosecurity. She recognises that the sow herd was the right place to start to raise a pig that is PRRS negative.

“We don’t know all the answers, but it's time to look at that pig after it leaves the sow farm as we place it in the nursery and to grow-finish,” she said. “In part, we have evidence from other diseases, and even from PRRS itself, that what happens in grow-finish matters to the sow farms. There’s evidence that infections can spread from grow-finish to the sow farm, then the sow farms breed and wean positive pigs. Those positive pigs will again seed an area with virus and represent risk for other sow farms in the region.”

The grow-finish phase holds many PRRS questions to be answered. Research is just starting in this area and more research will follow to try to better understand PRRS during this phase of pig growth.

Highlights from Symposium grow-finish researchers

“Incidence of PRRS wild-type virus in growing pigs and risk factors for infection”

Presenter: Jose Angulo, University of Minnesota

Dr Angulo is looking at the dynamics of PRRS infection in grow-finish or wean-finish herds. The PRRS-negative pigs in his study were located at operations in the Midwest.

“In his study, interestingly, he shows that about 50 percent of the herds will get infected with wild type virus after placement,” Dr Torremorell said. “He's also starting to look into the risk factors of why infections happen.”

There is an additional incentive to control PRRS in grow-finish because it affects mortality. From a risk factor standpoint, the data set is helping to understand the impact of how pigs are cared for, how pigs are unloaded, how location plays a role, etc. It’s important to learn what farmers must do and/or protocols to implement to help keep pigs negative after placement, she said.

“It was insightful that about 50 percent of the sites will have wild type virus unless we do something about it,” she said.

“Evolution of PRRS viruses in growing pigs”

Presenter: Mariana Kikuti, University of Minnesota

Dr Kikuti’s focus is on understanding virus evolution in grow-finish sites. She presented interesting information about understanding what sequencing means in grow-finish.

“Obviously we have enough sequence samples to understand or interpret the sequencing, but it tells us that these viruses are not very stable,” said Dr Torremorell. “Some variants of the PRRS virus do not seem to change very much, but other variants change a lot. [Dr Kikuti] is focusing on trying to associate whether some of those variants have a much higher impact on production or not. To understand that, we still need to work on the tools to analyse those variants of PRRS virus.”

“Controlling PRRS in growing pigs and dynamics of virus infection”

Presenter: Cesar Moura, Iowa State University

Dr Moura has started looking into not just the dynamics of the PRRS virus in grow-finish but also how to control the virus in pigs that originated from both stable herds and non-stable herds.

“Interestingly in that study, the incidence of infections was much higher than the one presented in the herds in the Midwest,” said Dr. Torremorell. “In his study, the incidence of the number of sites that would get infected with PRRS was higher than 90 percent, so it's a lot of sites that would become positive with PRRS. It just tells you that those infections are very prevalent.”

Dr Moura has also started exploring the use of a vaccine to control PRRS. More than 90 percent of the sites will vaccinate for PRRS. What was unique in this study, and goes against conventional wisdom, is they used a two-dose vaccination of PRRS, not one. This was done in pigs that originated from acutely infected farms and stable farms.

“We saw in those cases that vaccination actually was helpful to lower mortality, which was very, very encouraging,” explained Dr Torremorell. “Often you are in the middle of a PRRS break on a sow farm, and it's very frustrating because you see pigs dying and doing very poorly, but this study shows that by having two doses of vaccine, those pigs are doing better than if they had only one dose of vaccine.”

"Drivers of wean-to-finish mortality and the impact of disease status"

Presenter: Edison Magalhaes, Iowa State University

Dr Magalhaes’ presentation was not specific to PRRS, but he spoke about big data and how to integrate the different databases that these production systems have. By developing a better system, big data set could do a better job predicting mortality and which mortality factors matter, taking into consideration just not a single aspect of a disease or production system but looking at it comprehensively.

“Diseases are complex, and we need to have multiple sources of data and information if we really want to advance our efforts to control PRRS and/or other diseases,” said Dr Torremorell.

Opportunity in grow-finish

Grow-finish is an opportunity - not to abandon what has been learned in sow herds, but to start understanding more about what happens in grow-finish, said Dr Torremorell.

“Grow-finish, from a biosecurity perspective, is probably our weakness as an industry,” she noted. “That's where we have a lot of the pigs, and we still don't put a lot of effort into biosecurity. I'm not just thinking about PRRS but other diseases too. Unless we start tightening up or putting more effort into what happens in grow-finish, it will be very hard to keep sow farms negative or protected in the long run.”