Testing cortisol levels in the hair of young pigs could help select animals for breeding programmes to improve responses to stressors in their lives.
As the pork industry upscales to meet growing demand, it faces a welfare challenge as pigs experience stress from routine husbandry practices such as weaning, transportation, social interactions and temperature fluctuations. These factors have been shown to reduce health, growth and productivity.
A study by researchers at leading U.S. and Canadian universities used 889 Yorkshire × Landrace F1 piglets, a prime commercial breed, organised in batches by each of seven breeding companies. They kept the pigs under strict quarantine so that only stress unrelated to disease was studied, with each batch of piglets born at a similar time and experiencing the same transportation and housing.
Behaviour meets biology
When the piglets were around 27 days old, the researchers tested the animals’ coping style when placed in a V-shaped restrainer on its back, recording their number of vocalisations (squeals and grunts), as well as their struggles. At 40 days old, they shaved hair from each of them, which they then tested for stress hormone levels. This time point was selected to capture stress hormones caused by the non-infectious stressors early in their lives.
To complement the results from the hair hormone samples and behaviour testing, they used a whole-genome study to link traits of interest to small genetic variations in the pigs.
Pinpointing the genetics of stress response
They found that cortisol levels were correlated to the squeals and grunts of the pigs under stress but not with their struggles. Their genomic studies identified a specific region of DNA strongly associated with hair cortisol levels, and an even finer variation linked to the glucocorticoid receptor gene (NR3C1), which provides instructions for making a protein regulating stress response.
“This study is the first to report the genetic basis of stress hormone levels in hair of young and clinically healthy pigs. Results suggest that the level of cortisol in hair of young and clinically healthy pigs that are responding to non-infectious stressors is a potential genetic indicator of their coping response style,” the scientists wrote in the journal Genetics.
“Based on heritability estimates of these retroactive measures of stress response, these results highlight the potential of using stress hormone traits from hair to select for pigs that cope better with non-infectious stress.”
Implications for breeding programmes
The non-invasive use of hair hormone analysis as a retrospective means of assessing stress response “could be of high value in swine breeding programmes,” they noted, especially given selection is preferably done when the animals are still young and when they are under disease-free environments, as in the study. However, there is still work to be done, with the research team planning to flip the study design on its head to focus on pigs’ stress responses to infection.
Key takeaways
- Hair cortisol levels reflected pigs’ vocal stress responses during restraint.
- Researchers identified genetic regions linked to stress hormone levels.
- Variants near NR3C1 were associated with cortisol-based stress responses.
- Hair sampling offers a non-invasive tool for early-life stress assessment.
- Findings could inform breeding for pigs better able to cope with stress.
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