Improving performance under commercial conditions is a fundamental goal of Topigs Norsvin’s breeding program. One of the ways that Topigs Norsvin addresses this goal is by selecting for enhanced, general robustness. This strategy includes selecting for enhanced performance (including survival) during various phases of production, but also based on specific health traits, like conformation traits, body condition score, and reduced susceptibility to osteochondrosis and uterine prolapse. The newest addition to this list of target traits is robustness to disease.
At Topigs Norsvin, we define robustness to disease as the ability to maintain performance in the face of a disease challenge, or to recover quickly following exposure. In this sense, robustness is not specific to a certain pathogen, but refers to animals that are simply better at responding to disease in general, whether caused by a viral pathogen, bacterial pathogen, or other disease-causing agent. This approach relies on the use of traditional breeding; a methodology already used by our organization, and others, to facilitate genetic improvement in economically important traits and is globally accepted as an effective way to improve heritable traits in animal populations. Substantial evidence from literature, but also from our own research trials, shows that robustness to disease is heritable and, therefore, can be improved using traditional breeding strategies.
In fact, results from disease research trials conducted by (or in collaboration with) Topigs Norsvin, reveal substantial, natural variation in how pigs respond to a multifactorial disease challenge. Pigs in these trials were exposed to PRRS virus, and naturally co-infected with viral and bacterial pathogens. Therefore, data collected from these experiments capture variation in how pigs respond to real-world challenge scenarios with major swine diseases. Data collected from these trials are used to derive an individual’s genetic merit (i.e. breeding value) for overall robustness to disease, in the same way that genetic merit is estimated for growth, back fat, and other performance traits.
In a recent “proof of concept” study, breeding values for overall robustness to disease were estimated for Topigs Norsvin boar lines at a single stud. Boars were then ranked based on their breeding value for this trait: the top 30 boars were selected as sires for the “High Robustness” group, and the bottom 30 as sires for the “Low Robustness” group. At approximately seven weeks of age, progeny of these boars were exposed to a highly pathogenic strain of PRRS virus and naturally infected with a suite of viral and bacterial pathogens, including influenza, Streptococcus suis, Pasteurella multocida, and Glaesserella parasuis, among others. Results from this trial revealed up to a 10% difference in mortality rate between High- vs. Low-Robust progeny groups sired by one of Topigs Norsvin’s genetic lines.
In summary, results from this study, and previous trials, show that selection for enhanced, natural robustness to disease is an effective genetic solution for enhancing robustness to disease. In fact, selecting pigs for better general response to disease, is the only way to prepare for future (unknown) pathogen challenges. The aim of this breeding strategy is not to achieve complete resistance to a specific pathogen but, rather, to breed pigs that are able to maintain performance, despite disease status. This strategy avoids putting pressure on individual pathogens to mutate into alternative forms with, potentially, even higher pathogenicity.
Development of this breeding strategy is currently underway at Topigs Norsvin and will be implemented using the same, proven methodology already used to make genetic improvement in other traits included in our breeding goal. Selection for enhanced, overall robustness to disease will improve robustness under various disease challenge scenarios, including exposure to viral pathogens, bacterial pathogens, or a combination. Therefore, this breeding strategy has direct implications for improving performance under field conditions, while also reducing dependency on antibiotic usage. Selection for enhanced, overall robustness to disease is a natural genetic solution for improving pig health and welfare for diseases now, and in the future.
