Researchers, farmers and other stakeholders all have roles to play in addressing this production challenge.
Swine industry stakeholders around the world are working to tackle a big issue: finding a way to consistently improve pigs’ disease resiliency.
“Resilience, also sometimes referred to as robustness, is the ability of an animal to maintain productivity or performance when exposed to disease or other stressors (e.g., heat or cold stress),” says Dr. Jack Dekkers in an email to Better Pork. He’s a professor and the leader of the animal breeding and genetics group at Iowa State University.
“When exposed (to disease), some pigs that get sick recover quickly and keep on going. They’re resilient animals,” Dekkers says.
“Two main biological factors contribute to resilience: resistance and tolerance,” he says.
“Resistance is the ability of an animal to prevent (resist) infection or to reduce the ability of a pathogen (virus, bacteria) to establish itself and replicate within the animal. Disease resistance is often thought to be an all-or-none situation: when exposed to disease, an animal either gets infected or does not.
“In nature, however, there are different degrees of resistance,” he explains. “When pigs are injected with the same amount of the porcine reproductive and respiratory syndrome virus (PRRSV), it does well in some pigs. (But it) has difficulty replicating in other pigs because of their immune defenses, which can be measured by the amount of virus found in blood after infection.
“Tolerance, on the other hand, is the ability of an animal to minimize or overcome the damage created by a certain amount of pathogen present in an animal,” he says.
“It is very difficult to measure resistance or tolerance directly,” but resilience can be studied “by measuring the performance of animals in a barn in which pathogens are present,” he says. These performance metrics can include factors such as growth and mortality rates.
One of the key sources of research is the natural disease challenge model in Deschambault, Que.
Beginning in 2015, this challenge occurred at a wean-to-finish research station, where technicians seeded the animals with diseases common to the Canadian commercial industry. The diseases included PRRSV, influenzas H1N1 and H3N2, post-weaning E. coli, and Lawsonia intracellularis (ileitis).
Dr. John Harding, a professor at the University of Saskatchewan’s Western College of Veterinary Medicine, studied the project alongside Dekkers and others. Harding discussed the model in his paper, titled “The natural disease challenge model for evaluating resilience,” for the 2020 Banff Pork Seminar.
Swine researchers made several important findings during the challenge, Harding’s article indicates.
First, the “removal of direct contact between shedding and naïve pigs” is an “effective strategy to reduce challenges,” he says.
Further, “good operational biosecurity, including filtration and positive pressure ventilation, has been sufficient to maintain PRRSV freedom in an isolated room built within a PRRSV-positive farm,” he says.
So, resiliency on the farm involves limiting disease spread and understanding how environmental factors contribute as well.
Producers can use other herd management techniques to improve resiliency, says Gary Stordy, the director of government and corporate affairs at the Canadian Pork Council. These practices include “controlled access to certain parts of the property, the changing of clothes, etc.,” he says. These types of “subtle changes add up to improve biosecurity.”
Staff “compliance to well-established biosecurity routines … is essential,” he says.
Seasonal variation in disease is clear, “predictable and fairly dramatic,” the challenge model shows. In other words, the level of challenge is higher in the winter when barns are closed up and conditions get better in the summer, Harding adds in a Better Pork interview.
Genetic factors may also be at play, he suggests. “Improvement of disease resilience using genetic selection is possible, if appropriate measures of disease resilience can be obtained on animals within the high-health nucleus breeding farms,” he says in his article.
Farmers and scientists can use both novel measures, such as daily variation of feed intake and time at the feeder, and more traditional measures, such as growth rate and morbidity, to measure disease resilience, the natural disease challenge model team found.
The limitation appears to be that the “indicator traits must be heritable, have substantial genetic correlations with disease resilience, and should not interfere with other important traits,” Harding says in his paper.
“These indicator traits are something we can measure in the pig (to) predict resilience,” he tells Better Pork. “To make any genetic progress, it has to be done in a very high-health environment, and these are predictive of performance when the pig goes into a very dirty environment.”
“Indicator traits” can mean studying correlations between white blood cells and disease, the presence of specific antibodies (called natural antibodies) and other, more specialized indicators such as the disease-resistant assay of animals.
Some traits offer such promise to the industry, and genomics might be an answer, the challenge model shows. Researchers are trying to learn which genes help make some hogs more resilient than others.
“In general, estimates of heritability of disease resilience traits are low (less than 15 per cent), which means that 85 per cent of the factors that result in one pig being more resilient than another pig, even when they are in the same barn or even in the same pen, are not the result of differences in genetics,” Dekkers says.
However, the 15 per cent is important. “We found that the genetically top 20 per cent of pigs based on estimated breeding values for resilience had 11 per cent lower mortality (and) 0.75 fewer health treatments per pig. Those that survived reached market weight nine days earlier,” Dekkers says.
“We estimate this to be worth $18 per pig. So, selecting the top 20 per cent of pigs based on their genetics” could save that lost profit.
“To capitalize on the natural genetic variation that exists for resilience,” researchers have identified “some DNA markers … that allow breeders to select pigs that have better resistance or resilience to specific diseases … and more research is ongoing,” Dekkers explains.
“We are in the process of identifying early indicators of disease resilience that can be measured in healthy piglets,” he adds. “Having such a ‘diagnostic’ would allow breeders to identify pigs that have the genetic for disease resilience.”
So, while the science on genetic resiliency is just beginning, it appears extremely promising for the industry.
“The best thing producers can do to improve the resilience of their herds is to make sure that the pigs are not exposed to disease in the first place,” Dekkers says. But “it is obviously not feasible to keep all diseases out of a herd, and we also don’t have effective vaccines for all diseases. … That’s where genetic improvement of disease resilience comes in.”
If researchers can better determine the genetic predictors for disease resilience, then producers would face lower costs and fewer production hurdles.
While the research may still be a way off from on-farm application, producers are interested, Stordy says. They might consider disease resiliency in future genetic choices.
This decision must be made at the farm level, so stay tuned for more. BP
The Untold Story in Herd Health
Despite all the work underway on swine resiliency within the sector, threats to the overall biosecurity of a producer’s system remain key concerns.
Gary Stordy the director of government and corporate affairs at the Canadian Pork Council, worries about the cases of trespassing on farms. These transgressions happen across the country, he says.
“The untold story on the trespass issue is the mental stress that farmers go through, raising animals only to be subject to a form of harassment for doing what they do every day, working to ensure animals remain healthy,” Stordy says.
The regions that deal with trespassers face “a difficult situation,” he says.
Producers want officials to act. For example, it’s not fair that producers must negotiate with trespassers to have them removed, Stordy says.
“Producers are interested in seeing Crown attorneys charging, prosecuting and convicting. … More has to be done across Canada,” he says. Right now, the situation “does not sit well.”
So, while researchers work to improve pigs’ genetic resiliency, and producers try to strengthen on-farm biosecurity, swine industry stakeholders call on the governments to do their part to protect herd health. BP