398 Characterizing the genomic background of climatic resilience in pigs through quantitative epigenetic models, novel traits, and biological validation studies.

Abstract Heat stress negatively impacts the welfare and productive efficiency of pigs at different life stages. However, lactating sows are at a greater risk of deleterious heat-stress effects due to a substantial increase in litter and piglet sizes and, consequently, greater lactation demand and metabolic heat production. Genomic selection has been very effective in speeding up the rates of genetic progress for productive and reproductive traits, but the lack of indicators of heat tolerance in the selection indexes could unfavorably impact the heat stress response of modern sows. The development of a sustainable breeding program requires the identification of novel traits and genomic evaluation strategies to genetically select for improved heat tolerance. We have previously provided evidence of genetic variability for heat stress response, both in gestating sows and growing/finishing pigs, based on routinely-recorded performance data and environmental gradient variables derived from public databases. As the heritability estimates for fertility traits are substantially lower compared to growth traits (and consequently, heat tolerance based on reproductive traits), we have identified novel phenotypes and biomarkers that better represent the behavioral and physiological mechanisms of heat stress response in both growing/finishing pigs and lactating sows raised in climatically-challenging regions. Heat stress and feed efficiency are regulated by biological networks that starts with the host genotype, includes the gut microbiome, and is manifested in behavioral changes, which ultimately affects productivity and animal welfare. In our work we follow an integrated approach to study the biological background of heat stress connecting pig genomic, behavioral measures, epigenomics, and deep phenotyping. We will: 1) provide a comprehensive description of the environmental-gradient variables and critical periods fitted in genomic evaluations of heat tolerance as well as the accuracy of genomic breeding values; 2) describe the genetic background of various indicators of heat tolerance followed by comprehensive biological validations; 3) describe epigenetic variance due to heat stress based on quantitative modeling, and 4) make recommendations for the implementation of genomic selection for improved heat tolerance in pigs.