Herd immunity in pigs: A case study for getting America back to work

(Image by National Pork Board and the Pork Checkoff; created in Canva)

By Jennifer Shike
Farm Journal’s PORK


How does herd immunity in pigs apply to COVID-19? Some veterinarians say it has everything to do with this current pandemic situation.

“We’ve been working on herd immunity in the swine industry for decades,” says Tim Loula, DVM, of Swine Vet Center in St. Peter, Minn. “We use population medicine and do complex disease eradications on pig farms. About 20 years ago, the U.S. swine industry accomplished a national Pseudorabies virus eradication, a government program, to rid the U.S. of this disease. We have also worked with clients over the last 20 years to eradicate atrophic rhinitis, Actinobacillus pleuropneumoniae (APP) and swine dysentery. Today we perform eradications for porcine epidemic diarrhea (PEDv) and porcine reproductive and respiratory syndrome (PRRSv) and Mycoplasma.”

He says the key is understanding the disease status of each pig and population, and then working on a plan to get every pig “on the same page.”

After the first cases of COVID-19 were discovered at the Smithfield Foods pork processing plant in Sioux Falls, S.D., Loula and Dave Bomgaars of RC Family Farms reached out to the healthcare industry to visit with doctors about COVID-19. Doctors from Sanford Medical in South Dakota joined Loula, Bomgaars and a few other swine industry leaders in conference calls to formulate a plan using the best science available.

With their experience in population medicine, Loula hoped that if they all put their minds together, they could find some solutions or at least develop a plan to move forward. Together, the veterinarians and doctors shared flow charts of how they would interpret best testing procedures for plant workers.

Loula merged those ideas into a testing algorithm to help understand what’s going on in the packing plant populations. He says the algorithm assumes adequate availability of tests, both PCR (a test that would show if virus is present) and Elisa (a test that would show if antibodies to the virus are present).

“This situation is very serious. People are getting sick and some are dying,” Loula says. “We have to use all the science that we can and use the concept of population medicine to our advantage.”

How does population medicine work?

In their testing algorithm, the key is knowing every person’s status regarding the virus.

“We need to test every worker for the virus (PCR test) and for antibodies. This would allow us to group people into one of three buckets – positives, negatives (naïve) or immune (positive for antibodies),” Loula says. “Then, once you get that information back on your employees, you manage it like a pig farmer would.”

Managing people like pigs may be a difficult concept for people to accept at first, but Loula says producers manage different disease populations every day in their swine herds. He believes the process can work similarly in the human population.

The positive group indicates people who have the virus and are actively shedding it. People in that group would need to self-quarantine and be retested every seven days. Once their PCR tests come back negative, that indicates that their body has created antibodies and they could instantly move over into the immune group and get back out in the workforce.

The negative group is also referred to as “naïve” on a farm. These people have not contracted the virus and are the most vulnerable group. He says people in the negative group need to watch who they associate with, paying special attention to who they share rides with or hang out with when they aren’t at work.

Loula says he could even make a case for “negative” families in packing plant communities with COVID-19 outbreaks to move into a hotel or dormitory temporarily to protect themselves and to help keep these plants going.

The third group, the immune group, possess antibodies that provide immunity to the virus. This group can work with the negative group and not pose any threats, Loula says.

He adds that there is the possibility of someone having a positive PCR and a positive antibody test. This means they have a very low risk of shedding, but there is a possibility. He believes people who fall into this group could be segregated in a plant into a certain area of production or possibly work a different shift.

“We’ve got to figure out who has immunity and keep them working. They can keep these plants running,” he says. “The situation at hand with plant closures is dire. It’s a national emergency evolving right in front of our face.”

Source: Dr. Tim Loula, Swine Vet Center, and Sanford Health CLICK IMAGE TO ENLARGE

How can this help?

Knowledge is power. Loula believes helping not only the workers, but also communities, understand how herd immunity works will help alleviate unnecessary fear and hysteria.

“For example, in the Columbus Junction plant, workers may be concerned that two people died. That’s a legitimate fear. But if you could help people understand how you are separating the positives from the negative (naïve) and immune groups, then they can go to work without fear,” he says. “We need to tell a better story of the science involved.”

He says understanding the population of workers, in this example, would allow plants to make informed decisions about how to separate the positives from the negatives and immune.

But the key is that every worker needs to be tested. When only 700 workers out of 2,000 are tested, that only provides insight into a subset of the population and doesn’t reveal asymptomatic people who are actively shedding the virus. This also does not allow for a plan to be formulated or followed, he says.

More tests are needed

One of the greatest challenges now is a shortage of tests. Loula says there’s no question that health workers need to be tested first, but he believes people helping produce food should be next.

“We’re in danger of having to waste tons of food if we don’t get this figured out,” Loula says. “We need to have a plan in place to get plant workers tested. We need to test entire populations with both PCR and antibody tests. It’s time to get a plan, work the plan and if it’s not quite what we want, keep reworking it.”

Veterinary diagnostic labs have experience with high volume testing and rapid through-put. The main veterinary diagnostic labs have offered to help process tests for humans, he adds, noting, “It’s important that we not only get more tests, but we also need more labs to process tests.”

For example, Iowa State University’s Veterinary Diagnostic Laboratory is helping expand COVID-19 testing capacity to expedite test results at the State Hygienic Laboratory at the University of Iowa, the university reported in a release. Not only did they share extraction techniques, but they also shared instrumentation and the reagents needed for analysis.

As other industries return to production and non-essential workers begin getting together again, Loula believes another wave of the virus will spread. However, he believes the food industry could serve as a good model to help people know how to bring groups back together and not panic as the economy gets back up to speed again.

“We are the essential workers on the front line. We’re the ones experiencing this,” he says. “If we are successful in the food industry about how we work through it, then we could be the model for every other industry coming back.”

Strategies to help manage tough times created by COVID-19

The fallout from coronavirus disease 2019 (COVID-19) hit the US pork industry with a vengeance. Midwestern packing plants facing worker shortages from COVID-19 reduced processing and, in some cases, completely closed their doors.

In addition, labor on hog farms continues to be a big concern should positive COVID-19 cases develop.

Recognizing these serious issues, Swine Vet Center (SVC) in its latest SVC newsletter offers different strategies to help manage business through these challenging times.

Slow down ADG

Reduced packing plant operation means there are loads of hogs backed up and even cancelled, creating a backlog of hogs on the farm.

One way to handle this situation involves the intentional slow-down of average daily gain (ADG). Here are different ways to accomplish this:

  • Warm up room temperatures to 72° F to 76°
  • Cut back on square feet per pig.
  • Increase minerals, such as calcium chloride or monosodium phosphate, to slow intake.
  • Add fiber to reduce growth, using dried distillers’ grain if available or soy hulls.
  • Tighten up feeders to reduce intake.

Be sure to discuss these strategies with your nutritionist or SVC veterinarian to come up with a plan that makes sense for your system.

Reduce COVID-19 on farms

Farm workers are considered essential employees who work hard to keep a safe food supply during these uneasy times. Here are several ways to reduce transmission from employee to employee on sow farms:

  • Stagger entry times into farms so employees aren’t gathering before the shower.
  • Stagger break times and spread out tables in the break room.
  • Disinfect tables and counters after every use and at the end of the day. Disinfect the entire office daily and fumigate weekly.
  • Educate all employees on how the virus spreads.
  • Make sure employees are following the stay-at-home order to reduce exposure outside of work.
  • Split crews in half to a morning and evening crew. Half the crew works 4, 12-hour days and the other half of the crew works the next 4, 12-hour days. Workers are split (4 days on, 4 days off). This way if one crew member tests positive, only half the crew stays home for quarantine.

Wean-to-finish sites are taking multiple precautions to reduce the transmission of COVID-19 to employees.

  • Limit any unnecessary visitors.
  • Supervisors and veterinarians should plan their site visits to avoid contact with the caretakers or contract growers.
  • Reduce the size of vaccination crews and have them split up to different sites.
  • Follow social distancing.

Reduce costs

Most systems are looking at ways to reduce costs or inputs.

  • Review the usage of vaccinations, routine injectable antibiotics and feed-grade medications. Consult your SVC veterinarian before reducing any vaccinations or prevention strategies
  • Review sow-herd inventory and make sure you don’t have extra sows on the farm. There are instances where we can keep up with production but reduce the carrying cost of sows on that herd.
  • Check body condition across all herds and make sure you aren’t overfeeding sows.


More information

If you have other questions about how to deal with COVID-19 issues, visit:

National Pork Board COVID-19 resources

American Association of Swine Veterinarians COVID-19 resources

USDA APHIS Coordination Center to assist producers (affected by meat-processing plant closures)


What we learned from PED applies to COVID-19

Swine veterinarians and producers may feel déjà vu when they hear about the coronavirus disease 2019 (COVID-19) epidemic in the US.

Seven years ago, they battled a different coronavirus — porcine epidemic diarrhea (PED). Just like COVID-19, it spread quickly.

“We know how frustrating coronaviruses can be,” reported Laura Bruner, DVM, Swine Vet Center (SVC), St. Peter, Minnesota. “They are pretty hardy. When they have a naïve population to move through like PED did, it moves very rapidly.

“As the pork industry faced PED, we implemented a lot of biosecurity steps — washing more market trucks, limiting movements, more testing,” she explained. “We really improved our biosecurity, especially at the market level.”

The strategy to prevent COVID-19 infections is similar. Bruner advises everyone to follow the Centers for Disease Control and Prevention (CDC) recommendations for personal hygiene including frequent hand washing, limiting movement, staying home if sick and disinfecting the workplace.

In addition, the SVC office is taking workplace disinfection to a new level. “We are starting to fog our clinic with a product that kills microbes on contact. Just in case someone is sick, we can knock down that virus,” Bruner said.

She believes following the CDC guidelines in a hog facility will reduce COVID-19 infections in farm employees.

“I think you can function within a farm by using really good hygiene; even if one person gets sick, not everyone has to get sick,” she added.

Limiting contact in hog units

Some producers have changed work schedules to reduce contact between workers and limit the chance of a farm-wide outbreak.

“We’ve had some farms activate split shifts,” Bruner said. “Their crews are either split into a morning shift and afternoon shift or one half works three days and the other half works the next three days.

“If farms have not activated these shifts, they should limit contact between workers by staggering start times and breaks,” she added. “They also need to use social distancing on the job, like processing across from each other instead of next to each other.”

Contingency plans for dire situations

In the event of a COVID-19 outbreak at a client’s farm, the SVC veterinarians won’t be caught unprepared.

“Every week we have conference calls on what we need to think about for our clients; and every week we talk with our producers,” Bruner said.

They discuss contingency plans for everything from short staff at a farm to a processor shutdown.

Bruner says their biggest worry is a processor shutting down due to a worker shortage. She recommends everyone develop a plan to be prepared just in case it happens.

“Think of all the scenarios if you lost a week of marketing,” she explained. “It ends up being a double hit because you send in heavy pigs and it costs to feed them. So, what will be your plan for feeding those pigs differently at market end?”

If animal movement gets halted for a period of time, it is good to think through where the flow of pigs will go. Bruner says if space is available, it is possible to utilize nursery and farrowing to hold weaned pigs. But if you are tight, you may need to use the space in wean-to-finish barns. Identifying those now will help to handle this crisis if it occurs.

Short-staff planning

The other important contingency plan is for short staffing. “If we have multiple people who get sick, most times we have others come in to help, but that is not always possible,” Bruner said.

“We are asking producers if you normally have maybe nine people but only five are available, what are the tasks you need to do every day like feed, water, iron shots? We need to narrow the list to things you know you need to get done.

“We haven’t had a short staff yet, but we go through the concept with producers of what they need to do,” she added.

As the COVID-19 epidemic works its way through the country, Bruner believes people will learn from it and next year will be better.

“Just like with PED, we will have less coronavirus cases next year because people are recognizing how well these personal hygiene steps limit the spread of coronavirus,” she added.

More COVID-19 resources

For more information on ways to reduce the threat of COVID-19 in your hog operation, visit these websites:

U of MN Swine Disease Eradication Center


Inadequate iron supplements cause subclinical anemia in weaned pigs

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The standard 200 mg iron shot for baby pigs at processing may not be enough iron to last until weaning. Anemic pigs at weaning also grow slower in the nursery, reports Sam Holst, DVM, veterinarian with Swine Vet Center, St. Peter, Minnesota.

“The 200 mg injection of iron at processing was the gold standard…We need to relook at [it] to make sure we’re optimizing iron supplementation,” Holst said.

Checking hemoglobin

What he’s learned is no iron protocol works for all hog systems. Using a hand-held hemoglobin reader called HemoCue, Holst conducts diagnostic hemoglobin tests on-site for clients. He usually tests 20 to 30 piglets in a unit right before weaning.

“If we end up with greater than 20% or 30% of pigs iron-deficient or anemic at weaning, then we decide if we need to increase the dose,” he said. “Sometimes we review injection techniques with the staff to make sure [they are] giving a quality dose and not getting iron running out of the injection sites. Or we may decide to administer two doses of iron.”

The most common solution is increasing the dose. Holst sees farms use from 250 mg to 300 mg in a single injection. Going higher in a single dose may cause iron toxicity. If more iron is required, two doses are recommended.

Holst has clients using two doses, especially on farms with extended weaning ages. “If we’re getting out to 23, 24 days at wean age, we really tax that initial iron dose,” he explained. “In those situations, we have gone to either two 150 mg doses or two 200 mg doses.”

Subclinical anemia cases

The iron deficiencies Holst sees are not clinical cases where the deficiency is obvious, such as rough hair coats and pale pigs. Instead, it is subclinical anemia and not visually obvious.

“If we were to identify a group that had some significant anemia issues at weaning, we may go in and inject some iron [right after] weaning to try to catch them up,” he explained.

“There’s been some data that shows piglets that are anemic at weaning will actually grow slower throughout the nursery,” Holst continued. “So if it’s a severe group, it is advantageous to go in and supplement that group.”




Batch farrowing makes a comeback on small- to medium-sized sow farms

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The practice of farrowing sows in groups and not continuously is making a reappearance as small- to medium-sized sow farms seek ways to stay competitive, reports Paul Yeske, DVM, veterinarian with Swine Vet Center.

Yeske has seen many farms under 2,500 sows, and a few larger ones, switch to batch farrowing so they can wean enough pigs in a group to fill a large grow-finish facility. It really depends on what downstream flow looks like.

“It allows these farms to act like bigger farms and be able to run a site all-in, all-out and be reasonably sized,” he added.

Back to batch farrowing

Batch farrowing historically was popular when Yeske started his career.

“The trouble with batches is they fell apart because we didn’t have good control of the reproductive cycle of the gilts,” he said. “It took a lot of gilts and a lot of inventory to make sure you kept your batches full. When batches didn’t stay full…the breeding windows opened, and all of a sudden, you’re continuous farrowing.

“Now we have some tools that allow us to synchronize the gilts, and we can get them into the breeding window and…keep the groups very tight,” Yeske said.

Health benefits

The ability to break disease cycles with batch farrowing versus continuous flow offers attractive health benefits.

“You get the opportunity to have the farrowing house completely empty, and for some pathogens, it gives us the breaks we need,” Yeske said.

“Some of these disease cycles break down faster, and it helps to improve the health status, particularly in the wean-to-finish pigs,” he added. “Granted, the wean-to-finish is the motivation, but having these pathogens under control also benefits the sow herd.”

Improved wean-to-finish performance of batch-farrowed pigs makes them attractive to conventional-sized finishing sites. It makes the potential to not have to commingle flow or have multiple age groups on the same site.

The drawbacks

The downside to batch farrowing is a lot of the work falls within a 10-day timeframe, while continuous flow spreads the farrowing work over 4 weeks.

“For the people on the farrowing side, batch farrowing isn’t necessarily friendly,” Yeske said. “It makes it more of a challenge to manage the surges of work. One advantage, though, is that you do get the opportunity to specialize skills in these times and only concentrate on one activity at a time. This allows for better focus than having to balance multiple tasks at once.

“But from the wean-to-finishing side, you do get a single-source, good number of pigs. And as you go into [this], you need to think about it based upon the wean-to-finish performance,” he added.