Adaptation to heat in pig production: the genetic pathway – Pig Heat Tolerance PigHeaT

The PigHeaT project uses original biological resources. Pigs are produced from a backcross from a productive but poorly heat tolerant breed with a heat tolerant but poorly productive breed. These animals are characterised and reared in two INRA experimental units, located in tropical area and temperate area. These original experimental units give us the opportunity to study several heat-stressed situations. Chronic heat stress in tropical area, genotype by environmental interactions by comparing performance obtained in temperate and tropical areas, and acute heat stress such as heat waves. In this project, molecular tools (high density DNA arrays, ...) will be used. The obtained «Omic« data will be associated with phenotypes through statistical models.

The first main result is the identification of chromosomic regions influencing heat adaptation and production traits in pig. The second result is providing new knowledge to better understanding the physiological mechanism underlying heat adaptation. The whole results will provide biomarkers of heat tolerance. These molecular tools could be useful to predict heat adaptation and if they are validated, they could be implemented in breeding scheme to select for improving heat adaptation in pigs.

The main future prospect of the project is the most accurate mapping of genes influencing heat adaptation in pigs. From this map associated with relevant elements for better understanding of the physiological mechanisms underlying heat adaptation, molecular tools to predict pig's genetic potential to produce under heat constraint will be proposed.

A paper has been accepted in the EAAP congress, which will take place in Nantes on August 2013. This document deals with challenges to face for breeding for heat tolerance in pigs.

The climate is changing and according to the recent estimates from the IPCC, the likelihood of heat wave events is expected to increase both in number and in intensity. Temperature is projected to increase from 1.8 to 4.0°C from 1980-1999 to 2090-2099. Hence, heat stress-related costs in pig production will be amplified in the future, both in temperate areas (summer heat waves) and tropical areas (hot and humid environment). Meanwhile, world pig production is moving rapidly to tropical and subtropical regions reaching now more than 50% of the total production. The world development of pig production has been achieved through improvement of animal genetics and management in temperate countries. However, selection performed in optimally controlled conditions has increased the sensitivity of animals to high ambient temperature. Heat stressed pigs reduce their feed intake which impair their growth or reproduction performances. Management solutions are available to attenuate the effect of heat stress on pigs, such as environmental solutions (water or feeding management). However, these solutions are technically and economically difficult to implement. The genetic selection for improving environmental adaptation in pig production is the most promising long term option. The PigHeaT project aims 1) at identifying QTLs for heat adaptation, by examining direct responses to find genes involved in metabolic ways, indirect responses to find genes affecting growth or robustness to environmental variations, 2) at better understanding the physiological mechanisms underlying heat adaptation. It will provide tools for improving breeding strategies to face the upcoming global warming, and knowledge to better comprehend the physiological reactions of animals submitted to short and long term heat stress. The PigHeaT project is based on original biological resources and original experimental facilities. The studied population will be a backcross between Large White pigs, productive but poorly thermotolerant breed, and Creole pigs, low productive but highly thermotolerant breed. The progeny issued from this backcross will express all possible levels of thermal tolerance and production performances when submitted to heat stress, depending on the alleles received from their parents. High throughput phenotyping, metabolomics on all the progeny, and transcriptomics on a subset of extreme pigs selected on thermal tolerance response, will be applied. It will allow to refine the phenotypes and to achieve a high level of accuracy in QTL detection in the frame of the PigHeaT project. Additionally, the design will benefit from the unique combination of experimental facilities available at INRA: the first part of the project will rely on the backcross population raised in the experimental facilities located in the West Indies (Guadeloupe, tropical environment). The concomitant production of the same population in the experimental facilities available in temperate France (Charente Maritime) will allow the detection of genetic by environment (GxE) effects for the QTL detected in Guadeloupe. Moreover, a heat wave phenomenon will be systematically simulated in the temperate environment at the end of the growing period. As a result, chromosomal regions robust or susceptible to GxE interactions will be identified, GxE being either tropical vs temperate, or tropical vs heat wave. Finally, an integrated analysis of the (fine) phenotypes and QTL will be proposed to better understand the metabolic pathways involved in heat stress responses. The respective use of the QTL and biological knowledge in further breeding strategies will finally be considered.