Importance of Host Genetics to Population Health28 April 2014
CANADA - Population health is one of the most important factors to swine production and overall profitability. No matter how superior the genetics, a dead animal is a financial loss to the producer, writes Dr Nick Boddicker, PhD.
Good population health starts with healthy replacement breeding stock and a good biosecurity plan that can be properly executed. However, even with the best biosecurity plan, swine producers face disease challenges daily, be it Porcine Reproductive and Respiratory Syndrome (PRRS), Porcine Circovirus-Associated Disease (PCVAD), Swine Influenza, or the new hot topic, Porcine Epidemic Diarrhea Virus (PEDV).
Vaccination is one of the primary tools used to prevent disease outbreaks. However, for a vaccine to be most effective it needs to be given in the proper condition to the proper animals via the proper route at the proper dose and at the proper time. This gives the vaccine the best chance to stimulate an antibody response. Even if that is all done correctly, there are no vaccines that provide 100 per cent protection to all individuals.
On top that, there are viruses and bacteria that are constantly changing and highly variable like Influenza, PRRS, and Strept. Suis that make it difficult to create effective vaccines. Of the aforementioned diseases, Porcine Circovirus vaccines are the only ones that have truly been considered effective vaccine. Both influenza and PRRS viruses change rapidly and there is not a vaccine for either pathogen that is broad enough to cover the array of strains. When it comes to PED, there is not currently an effective vaccine on the market as there is still much to learn before an effective vaccine is developed.
With recent advancements in genomic technology, genetics may play a larger role in population health than ever before. Until recently, it was believed that many genes with small effects contributed to an immune response. Although it is still likely that many genes contribute to an immune response, there appear to be genes that have relatively large effects in the genome. Lewis et al. (2007) and Boddicker et al. (2012) have identified regions in the genome that have large effects in response to PRRS virus. Specifically, these regions play a role in reduced circulating virus load and increased weight gain.
Ideally, geneticists would like to create animals that are completely resistant to disease. However, this is highly unlikely due to the genetic variation across pathogens and swine population, and is arguably undesirable due to the likely consequences on production and reproduction traits. In current studies, researchers rely on pigs becoming infected with the pathogen of interest, either naturally or experimentally, to identify the animals with favorable phenotypes under challenge and relate those phenotypes to the animal’s genetic code.
These traits include viral clearance, antibody response, and typical production traits such as growth and sow performance. Through genomics, geneticist can identify animals that mount a good immune response to efficiently clear the pathogen, maintain sufficient growth, or have standard number born alive with minimal pre-weaning mortality, even under disease challenges. This is commonly called disease tolerance.
Before genomics is utilized, there must be evidence that the animals own genetics contributes to population variation, i.e. some pigs do better than others under a disease challenge. One of the sources of variation, among others is the animal’s breed. To my knowledge, there are no publications on breed differences with respect to PED. However, breed differences have been rumored, making PED a good disease to identify genomic regions associated with host response.
Good biosecurity and routine effective vaccination programs are efficient means for controlling disease outbreaks. With the onset of genomics, genetic selection is another tool that can be added to the arsenal in the war against disease. To win the war, it will take a joint effort between producers, geneticist, and veterinarians. There is no silver bullet when it comes to population health.
1) Boddicker, N., Waide, E.H., Rowland, R.R.R., Lunney, J.K., Garrick, D.J., Reecy, J.M., and Dekkers, J.C.M. 2012. Evidence for a major QTL associated with host response to Porcine Reproductive and Respiratory Syndrome Virus challenge. J. Anim. Sci. 90:1733-1746.
2) Lewis, C. R. G., M. Torremorell, L. Galina-Pantoja, N. Deeb, M. A. Mellencamp, A. L. Archibald, and S. Bishop. 2009. A genome- wide association analysis identifying SNPS for PRRS tolerance on a commercial pig farm. Proc. Assoc. Advmt. Anim. Breed. Genet 18:187–190.
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