If you thought “connecting the dots” could be challenging as a child, try matching over half a million genetic markers with traits of interest to the pork industry. That is the task facing researchers with a Genome Alberta-led study, as they apply genomics to increase disease resilience and sustainability in Canadian pork production.
“A big part of the project is using genome wide association studies (GWAS), a common tool for studying genetics in humans, animals and plants,” said Jian Cheng, a PhD candidate in the Department of Animal Science at Iowa State University. “We use 650,000 SNP markers [the most common type of DNA variant found in people and animals] to genotype pigs, determining which gene or genes are associated with our targeted phenotypes or characteristics.”
To accomplish this goal, scientists exposed pigs to a variety of naturally occurring pathogens in a research barn at CDPQ in Quebec and used GWAS to find associations between genomic regions and the targeted phenotype for disease resilience.
The results so far are promising, as researchers have detected many QTL (genomic regions responsible for the variation between animals for a quantitative trait) associated with growth under a disease challenge, as well as QTL related to carcass quality, such as lean yield.
“We have identified a number of QTL linked to disease resilience and immune capacity,” said Cheng.
More acronyms, anyone?
As part of their efforts, Cheng and his colleagues are focused on yet another acronym: MHC, which is short for major histocompatibility complex. This refers to a group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances.
“MHC is a very important genomic region in both humans and animals in relation to immune response. For example, when they transplant organs between people, it is important to find a match because the MHC will detect the new organ as foreign if there’s no match and provoke an immune response to reject it.”
It is within the MHC that researchers found a number of QTL related to disease resilience in pigs. Going forward, the plan is to select on these targeted QTL over multiple generations. In doing so, they can change the frequency of the favorable versions of these QTL and, ultimately, generate pigs with greater resilience to the multiple disease challenges in the pork industry.
While equipping pigs to fend off specific disease organisms that threaten their health would clearly have value, this study takes it a step further.
The value of variety
“This project involves collaboration among the seven breeding companies of PigGen Canada, CDPQ, and several universities, allowing us to expose pigs from these companies to the pathogens that can be present in typical pig barns. This is important because the MHC region is polymorphic, meaning that it harbors a wide range of genes and different versions of those genes. If you select for genes that are related to a specific disease, other regions of the MHC might also then be affected. As a result, pigs could wind up being more resistant to one disease and less resistant to others.”
Just as pigs in the real world are usually exposed to many pathogens simultaneously, the “Natural Disease Challenge Model” established at CDPQ provides for pathogen exposures that replicate on farm conditions. Through this process, scientists can gain a better understanding of the MHC and how it functions to help a pig fight off disease.
Simultaneous exposure to typical pig diseases not only makes this study unique, but it also makes the results highly relevant to today’s pork industry.
“Currently, in Canada and around the world, numerous diseases such as PPRSv, PEDv, and several bacterial diseases, such as streptococcus and salmonella, affect the health of pigs. Because these pathogens can impact both reproduction and production, they contribute to large economic losses for producers. If we can select for pigs that have better disease resilience, the pigs will be more robust and will possess greater immunity, allowing them to remain healthy in the face of disease exposure. Although this may take considerable time to achieve, our study is an important first step towards a healthier, more profitable pork sector down the road.”