Disease is a major threat to pig production worldwide. Disease breaks impact profitability, disrupt pig flows, and compromise animal welfare. Many different factors contribute to the spread of disease, such as rearing animals in high-hog dense areas, gaps in biosecurity, and pathogen mutation. For this reason, disease control is considered a multifactorial issue which, therefore, requires a combination of different types of solutions. One such solution is breeding pigs for enhanced, natural resilience to disease.
Disease resilience is defined as an animal’s ability to maintain performance in the face of a disease challenge, or to recover quickly following exposure. According to this definition, disease resilience 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. There is substantial evidence from the literature, and from our own research trials, that this type of general resilience to disease is heritable. This means that it’s possible to identify animals with superior genetic merit for disease resilience which, when mated, produce offspring that are naturally more resilient to disease. Disease resilience, like most health and welfare traits, is controlled by many different genes. Therefore, the only way to take advantage of the combined effect of these genes is by using genetic selection.
In 2018, Topigs Norsvin began developing a strategy to breed pigs for enhanced, natural disease resilience. This strategy requires collecting data in real-world challenge scenarios, including exposure to major swine diseases. Data collected in this way captures variation in how pigs respond to disease, and are used to derive an individual’s genetic merit (i.e. breeding value) for disease resilience. This is the same process used to estimate genetic merit for other traits, like growth, feed conversion, and litter size.
In a recent “proof of concept” study, breeding values for disease resilience were estimated for TN Duroc boars at a single stud in the USA. These breeding values were estimated using thousands of genotypic and phenotypic records collected under diseased challenged conditions. Boars were then ranked based on their breeding value for disease resilience and the top 30 (aka “High Resilience”) and bottom 30 (aka “Low Resilience”) boars were selected to be used as sires. Topigs Norsvin TN70 females were inseminated with semen collected from either High or Low Resilient boars to produce pigs in the High vs. Low Resilience progeny group, respectively.
At weaning, pigs were placed in a commercial research barn and tissue was collected for genotyping. At approximately 51 days of age, pigs were exposed to PRRSV 1-8-4 and followed until marketing. In addition to PRRSV challenge, numerous secondary bacterial and viral pathogens were detected throughout the study, including Streptococcus suis, Pasteurella multocida, Glaesserella parasuis, and influenza A, among others. Repeated, individual body weight measurements, individual treatments, and mortality events were recorded throughout the trial.
Results from this study showed that the progeny of High Resilience boars had consistently greater ADG than the progeny of Low Resilience boars, whether evaluated for the first month post-challenge only, the entire challenge period (inoculation to market), or from wean-to-market (Table 1). The greatest difference in ADG was observed for the challenge period, where High Resilient progeny grew, on average,1.55 lbs/day, vs. 1.35 lbs/day for Low Resilient progeny. Progeny of boars selected for High Resilience also had a significantly lower treatment rate (i.e. the percent of pigs requiring one or more antibiotic treatments) for the first month post-challenge, and the entire wean-to-market period. Lastly, pigs sired by High Resilience boars had significantly lower mortality rate for each period evaluated, with an overall (wean-to-market) mortality rate of 24%, vs. 35% for pigs sired by Low Resilience boars.
In summary, pigs sired by High Resilient boars had significantly faster growth, lower treatment rate, and lower mortality rate than pigs sired by Low Resilient boars. Results from this study demonstrate that selecting pigs based on genetic merit for disease resilience is not only possible, but can be used to create substantial contrasts between pigs sired by boars selected based on genetic merit for this trait. 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 Topigs Norsvin’s breeding goal. Selection for enhanced disease resilience is a natural genetic solution for improving pig health and welfare for diseases now, and in the future.
Table 1: Least-squares means and standard errors for average daily gain (ADG), treatment rate (percent of pigs requiring one or more antibiotic treatments), and mortality rate (percent of pigs that died), for pigs sired by boars selected based on high vs. low genetic merit for disease resilience.
To see additional results from this trial, click here to see the trial summary.
