How to minimize summer’s impact on sow fertility

Sow reproductive performance drops off in the summer, and this year will be no different, according to Paul Yeske, DVM, Swine Vet Center, St. Peter, Minnesota.

“We typically see reproductive performance drop off as we get to week 29 through 40,” he said. “With hot weather in late May and early June, we may see it a little quicker than normal for us in the upper Midwest.”

To minimize the impact of seasonal infertility, Yeske recommends producers take steps to keep November and December farrowing numbers up.

Environmental impact

One main cause of seasonal infertility is overall environmental temperature, which can be handled several ways.

“Mitigation steps include increasing ventilation rates and using evaporative cooling like cool cells, drip coolers or misters or a combination to keep sows as comfortable as possible,” Yeske said.

“Typically, we see in this period more 21-day returns to heat, so sows are not conceiving as well,” he explained.

“In the past, those numbers would be more exaggerated. Today, they are in the range of 2% to 5% and not a huge number, but it does show up this time of year.”

Day length changes

The other cause of seasonal infertility is the change in day length.

“As day length shortens, the sows don’t want to be pregnant and farrow in the middle of the winter,” Yeske said.

“We see more irregular recycles. The sows were pregnant, and they either lose the pregnancy or reabsorb the litters.

“We want to be sure to identify these animals and decide if we are either going to get them rebred and back into the system, or cull them because performance is low,” he added. “We don’t want them sitting around taking up space and time.”

Yeske recommends heat checking early, because there are more 21-day recycles, and being diligent with second pregnancy checks around 50 to 60 days to pick up early pregnancy losses.

“Historically, we would see some sows not-in-pig as we get to November when those animals should be farrowing,” he explained.

“If we can get them identified now, then we don’t have them tie up space until November or December and not have litters.”

Some farms use lighting to help counter the changes in length of daylight. Timers keep lights on up to 16 hours a day in a bid to mimic the longest day of the year.

The impact of this lighting is hard to say for sure, but Yeske said many farms use this approach and it isn’t hard to do.

Increase breeding target if possible

Another option for minimizing seasonal infertility is to breed more animals if you have the room to do so.

“Farms will use their historical information to compensate by breeding, in general, 2% to 3% more animals, depending on what they’ve seen in the past,” Yeske explained.

Seasonal infertility used to be a much larger issue when boar services were required.

“Boars would get heat stressed, and semen quality would go down,” he said. “With nearly everything switching over to artificial insemination, we’ve been able to mitigate that issue.

“But seasonal infertility still shows up every year,” he added. “While the losses aren’t big, there are always some…so the quicker we get them identified, the quicker we can get animals bred back and into the system and be as efficient as possible.”


Dry fog with common disinfectants decontaminates supply rooms

Hog producers discouraged to learn foggers don’t fully disinfect a supply room should not close the door on the biosecurity method yet.

New research spearheaded by Erin Kettelkamp, DVM, with Swine Vet Center, found a better solution for disinfecting supplies in a hog facility.

“In previous research, all commercial foggers resulted in incomplete disinfectant contact to all sides of objects,” reported Kettelkamp, who earned her DVM from the University of Illinois. While at the university, she studied fogger decontamination efficacy and identified a new protocol for disinfection.

Particle size, disinfectants studied

Kettelkamp’s research considered two questions. The first was how the aerosol particle size impacted fumigation. The second question was the composition of the disinfectant.

“First, particle size does matter and the smaller the better,” she said. “We used a dry fog that is a particle under 10 microns. A fine mist is 100 microns, so this is a particle you can’t quite see. But when you have them in a high frequency, it creates a dense fog, which is important because those small particles move through the room. Instead of bursting at the first surface they come into contact with, the particles permeate the room and achieve disinfection.”

For the second question, Kettelkamp tested a combination of hydrogen peroxide and peracetic acid, which is used in food processing, dairy and beverage industries for disinfection. After testing different concentrations of both, she found one that inactivated pathogens.

“There is a ready-to-use formula…but it wasn’t strong enough,” she said. “We increased our concentration by doubling our hydrogen peroxide and quadrupling our peracetic acid.”

She also tested using hydrogen peroxide alone at the high rate, but it was not effective. Disinfection depends on peracetic acid in the mixture, she added.

Kettelkamp used a geobacillus indicator strip with a robust bacterial pathogen colony to test the results. She validated the results with a porcine reproductive and respiratory syndrome (PRRS) modified live virus vaccine and manure. The dry fog inactivated the indicator strip and PRRS while also disinfecting the manure.

Dry fog best

“If a producer wants to continue to use a fogging chamber, I recommend working with a veterinarian on using a type of fogger to decrease the particle size,” Kettelkamp said. “Hurricane foggers can be adjusted to smaller particle sizes and will be more effective (than larger sizes).

“The gold standard is a dry fog for best permeation throughout the room,” she added. “Specifically in this model, the hydrogen peroxide and peracetic acid worked well.”

Another benefit to a dry-fog system is it only needs an air compressor for operation. And after treatment, clean-up is easy because dry fog produces no residue or liquid pools that need to be cleaned up.


Based on her research, Kettelkamp reports complete disinfection by aerosol decontamination occurs with droplet sizes less than 14 microns. Optimal results require a droplet size that’s less than 6 microns, also considered a dry fog.

In addition, the disinfectant concentrations for decontamination must be hydrogen peroxide levels above 4.2 ppm and peracetic acid levels at 0.13 ppm.

“Fogging certainly isn’t the only method to decontaminate items as they come into farms,” she added. “Other methods such as hand spraying items and time and temperature to let items decontaminate are also effective. Fogging could also be used with other methods to achieve a really robust decontamination.”

For more information, you can view Kettelkamp’s research presented at the 2021 American Association of Swine Veterinarians meeting here:

Nasty PRRS variant continues to spread undeterred by summer’s heat

The virulent porcine reproductive and respiratory syndrome (PRRS) variant identified as PRRS 1-4-4 continues its destructive march through hog farms, even in the heat of summer.

The PRRS variant first struck herds in Minnesota and northern Iowa this past winter, and while producers and veterinarians hoped it would calm down in warm weather, latest data suggests things aren’t so simple.

“Even when it was 99°, we were getting calls about PRRS breaks,” reported Laura Bruner, DVM, with Swine Vet Center in St. Peter, Minnesota.

“It’s unprecedented; it’s unusual,” she continued. “This virus is walking past normal biosecurity practices such as on-farm biosecurity, trucking biosecurity, air filtration and feed mitigation.”

Survey shows variant’s hot spread

Alarmed by the continued PRRS 1-4-4 outbreaks, Bruner surveyed her peers of 15 veterinarians in the US to understand the variant’s reach. She was shocked by the results.

“In just over a month during the warm time of the year, we had 107,000 sows break with PRRS 1-4-4, and I believe that is an underestimation,” Bruner said.

“When you talk to practitioners about it, they have farms breaking with the variant that have never broke with PRRS before, and for some farms it’s been decades or never.

“Also interesting is how many nursery breaks there are,” she continued. “I can count on both hands in my career how many lateral field infections have happened in the nursery. It has caused more mortality and makes these nursery pigs quite a bit sicker than what we have seen other viruses do in the past.”

Another unusual detail of these outbreaks is the consistency of the PRRS 1-4-4 variant.

“Historically, if you have a sow-farm break, you call another veterinarian and compare sequences,” Bruner explained. “Rarely do they match. But with this one, it’s frequently over 99% to 100% a match. I had one farm in southern Minnesota that was a 100% match to a PRRS virus in northern Minnesota.”

Time to collaborate

Armed with her PRRS 1-4-4 survey results, Bruner sought help from Cesar Corzo, DVM, at the University of Minnesota. Corzo works with the Morrison Swine Health Monitoring Project, which monitors the incidence of swine disease such as PRRS. He set up a meeting at World Pork Expo (WPX) with other veterinarians and swine disease researchers to discuss the PRRS variant.

“My purpose of getting that meeting together was to collaborate and learn from each other,” Bruner said.

“We’ve learned we don’t know everything about PRRS, and specifically this virus because it does seem to be different. It is a game changer, just like PED (porcine epidemic diarrhea) when it arrived.”

Bruner hopes new research discussed during the WPX meeting will shed light on the variant’s unusual virulence. But for now, collaboration among practitioners will help fill in answers.

“We need to learn from who breaks with 1-4-4 and who doesn’t,” she said. “And we need to learn the successes and failures of their investigations.

“We need to go all the way back to the beginning and ask: Do our normal biosecurity practices work? Does our normal disinfection work? Do the filters we use today work? What’s different?”

Tighten biosecurity

With the variant’s threat to hog farms, Bruner recommends producers use this as an opportunity to improve biosecurity on the farm.

“Take a hard look at your biosecurity for any weaknesses and get them corrected,” she said. “We need to be looking at all the major inputs into the farm like people, feed, water and air as a source of infection.

“We are unsure of feed as a route of entry and haven’t done research on PRRS specifically in feed. I think it is worth considering a feed mitigant for sow farms and gilt-development units. We know that there are ingredients that provide a better environment for virus survivability than others and those need to be investigated.”

For farms that broke with PRRS 1-4-4 last winter, Bruner said it is still too early to know if the virus leaves the farm or if it will be difficult to eradicate.

For more information about PRRS 1-4-4, visit:

Highly infectious PRRS variant causes high mortalities on sow farms

New PRRS 1-4-4 L1C variant presents dramatic symptoms, quick spread

Virulent PRRS outbreaks in grow-finish require fast action to cut losses