# Genetics of retroactive measures of stress response in pigs before and after exposure to a disease challenge

## TL;DR

This study investigates how genetic factors influence stress hormone levels in pigs under infectious and noninfectious stress, using hair samples to guide breeding for better stress resilience.

## Contribution

The study identifies a major QTL and genetic correlations for stress hormones in pigs under infectious and noninfectious stress.

## Key findings

- Heritability estimates for stress hormones in hair under infectious stress ranged from 0.01 to 0.27.
- A significant genetic correlation of 0.52 was found for cortisol levels between infectious and noninfectious stress.
- A major QTL near the glucocorticoid receptor gene was linked to reduced cortisol and cortisone under infectious stress.

## Abstract

This study explored the genetics of cortisol (CL), cortisone (CN), DHEA (DH), and DHEA-S (DS) in hair of 610 pigs that were grown while they were exposed to infectious stressors (IS) from a natural polymicrobial disease challenge. Results were then contrasted with previous results on hair from these same pigs grown while experiencing noninfectious stressors (NIS), such as weaning, castration, transportation, and mixing. All pigs were genotyped for 50 K SNPs and imputed to 650 K SNPs. Heritability estimates for hormone levels in hair grown under IS ranged from 0.01 for DS to 0.27 for CL. Estimates of genetic correlations between levels of a hormone in hair grown in response to IS vs NIS were not significantly different from zero and were highest, at 0.52, for CL. Genome-wide association studies identified the same major QTL for CL in response to IS that was previously found for response to NIS, near the glucocorticoid receptor gene. The minor allele at the lead SNPs (frequency = 9%) significantly (P < 0.001) reduced CL under IS by 30 ± 4% and CN by 23 ± 6%, had no significant effect on DH or DS, and drove the genetic correlation between CL in hair grown under NIS vs IS. A comparative gene set enrichment analysis (GSEA) approach revealed that genomic windows that were associated with active forms of the stress hormones (CL and DH) tended to explain more variance during response to IS than to NIS, while the opposite was true for their inactive forms (CN and DS). These results may facilitate the selection of pigs that cope better with IS and NIS using hormone levels in hair as a noninvasive sample.