Jiahong Sun: Genome-wide associations of hematological traits linked to growth and post-weaning diarrhea in pigs
Email: jiahong.sun@sund.ku.dk
Date defended: 26 August 2026
THE PROJECT
Do you know how hard it is for a piglet to survive during its early growth?
At weaning, piglets have to live without their mothers and suddenly find themselves surrounded by unfamiliar animals. Can you imagine how stressful that can be? When we enter a new environment, we may experience digestive problems because of changes in diet and exposure to different bacteria. Piglets face similar challenges. However, some piglets are more robust than others. They are stronger, grow faster, and remain healthier. One important reason may be their genetic background.
This project aims to identify these robust piglets and understand the biological mechanisms behind their resilience. We also aim to identify genetic predictors of post-weaning diarrhea. With this knowledge, farmers may be able to provide more targeted care to vulnerable piglets, while breeding companies could select for more robust pigs that are better able to cope with stressful and unhealthy conditions.
THE PURPOSE
The purpose of this PhD project was to better understand why some pigs are more resilient than others during this weaning transition. The project combined information on growth, blood characteristics, genetics and disease records from more than 2,000 pigs. By studying these different layers together, the research aimed to identify biological and genetic factors linked to healthier growth and lower susceptibility to post-weaning diarrhea. In the longer term, this knowledge may contribute to breeding and management strategies that support healthier and more robust pigs.
THE RESULTS
The project showed that simple blood measurements can provide useful information about how piglets respond to the challenges around weaning. Several blood characteristics were associated with growth and the risk of post-weaning diarrhea. The research also identified genetic regions influencing these blood traits, showing that part of the variation between pigs is inherited.
Importantly, the results suggest that blood characteristics can act as a bridge between genetics and later health. For example, differences in red blood cell-related and immune-related measurements partly explained the relationship between early growth and subsequent diarrhea risk. Genetic information also helped distinguish pigs with different risks of post-weaning diarrhea, although prediction was still far from perfect. This highlights both the potential and the complexity of using genomic information to predict animal health.
Overall, the findings show that resilience is not determined by a single gene or a single measurement. Instead, it results from the interaction between genetics, physiology, growth and the environment. The project therefore provides a more integrated picture of how piglets cope with the stressful transition from suckling to independent life.
THE FUTURE
The next step is to understand more precisely how the genetic regions identified in this project influence blood characteristics, growth and disease resistance. Larger populations and additional biological information could help identify the genes and mechanisms behind these associations. It will also be important to test the findings in other pig populations and production systems. This will show whether the same biological indicators and genetic markers can be used more broadly.
In the future, information from genetics, blood measurements, growth and health records could potentially be combined to identify pigs that are better able to cope with challenges around weaning. Rather than selecting animals based only on growth performance, breeding programmes could increasingly consider robustness and health as well.
The long-term goal is not simply to predict which pigs will become sick, but to understand what makes an animal resilient. Better knowledge of resilience could support breeding and management strategies that improve animal health and welfare and, potentially, reduce the need for antimicrobial treatment.
The research therefore provides a foundation for moving towards pig production in which good performance and good health are considered together.
