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The present study aimed at investigating the impact of heat challenges on gut microbiota composition in growing pigs and its relationship with pigs’ performance and thermoregulation responses. From a total of 10 F1 sire families, 558 and 564 backcross Large White × Créole pigs were raised and phenotyped from 11 to 23 wk of age in temperate (TEMP) and in tropical (TROP) climates, respectively. In TEMP, all pigs were subjected to an acute heat challenge (3 wk at 29 °C) from 23 to 26 wk of age. Feces samples were collected at 23 wk of age both in TEMP and TROP climate (TEMP23 and TROP23 samples, respectively) and at 26 wk of age in TEMP climate (TEMP26 samples) for 16S rRNA analyses of fecal microbiota composition. The fecal microbiota composition significantly differed between the 3 environments. Using a generalized linear model on microbiota composition, 182 operational taxonomic units (OTU) and 2 pathways were differentially abundant between TEMP23 and TEMP26, and 1,296 OTU and 20 pathways between TEMP23 and TROP23. Using fecal samples collected at 23 wk of age, pigs raised under the 2 climates were discriminated with 36 OTU using a sparse partial least square discriminant analysis that had a mean classification error-rate of 1.7%. In contrast, pigs in TEMP before the acute heat challenge could be discriminated from the pigs in TEMP after the heat challenge with 32 OTU and 9.3% error rate. The microbiota can be used as biomarker of heat stress exposition. Microbiota composition revealed that pigs were separated into 2 enterotypes. The enterotypes were represented in both climates. Whatever the climate, animals belonging to the Turicibacter–Sarcina–Clostridium sensu stricto dominated enterotype were 3.3 kg heavier (P < 0.05) at 11 wk of age than those belonging to the Lactobacillus-dominated enterotype. This latter enterotype was related to a 0.3 °C lower skin temperature (P < 0.05) at 23 wk of age. Following the acute heat challenge in TEMP, this enterotype had a less-stable rectal temperature (0.34 vs. 0.25 °C variation between weeks 23 and 24, P < 0.05) without affecting growth performance (P > 0.05). Instability of the enterotypes was observed in 34% of the pigs, switching from an enterotype to another between 23 and 26 wk of age after heat stress. Despite a lower microbial diversity, the Turicibacter–Sarcina–Clostridium sensu stricto dominated enterotype was better adapted to heat stress conditions with lower thermoregulation variations.

International audience; Heat stress affects pig health, welfare, and production, and thus the economic viability of the pig sector in many countries. Breeding for heat tolerance is a complex issue, increasingly important due to climate change and the development of pig production in tropical areas. Characterizing genetic determinism of heat tolerance would help building selection schemes dedicated to high performance in tropical areas. The main objective of our study was to estimate the genetic parameters for production and thermoregulation traits in two highly related growing pig populations reared in temperate (TEMP) or tropical humid (TROP) environment. Pigs came from a backcross population between Large White (LW, heat sensitive) and Creole (CR, heat tolerant) pigs. Phenotypic data were obtained on a total of 1,297 pigs using the same procedures in both environments, for body weight (BW, at weeks 11 and 23), daily feed intake (ADFI), backfat thickness (BFT, at weeks 19 and 23), cutaneous temperature (CT, at weeks 19 and 23), and rectal temperature (RT, at weeks 19, 21, and 23). Feed conversion ratio (FCR) and residual feed intake (RFI) were computed for the whole test period (11 to 23 wk). Criteria comparing the fits to the data revealed genotype × environment (G × E) interactions for most traits but not for FCR. The variance components were obtained using two different methods, a restricted maximum likelihood method and a Bayesian Markov chain Monte Carlo method, considering that traits are either similar or different in each environment. Regardless of the method, heritability estimates for production traits were moderate to high, except for FCR (lower than 0.18). Heritability estimates for RT were low to moderate, ranging from 0.04 to 0.34. The genetic correlations of each trait between environments generally differed from 1, except for FCR and ADG. For most thermoregulation traits, they also did not differ significantly from zero, suggesting that the main genetic bases of heat tolerance may vary in different environment. Within environments, the unfavorable genetic correlations between production traits and RT suggest an antagonism between the ability to maintain inner temperature and the ability to increase ADFI and ADG. However, greater RT were also associated to leaner pigs and better feed efficiency. Nevertheless, due to large inaccuracies of these estimations, larger cohorts would be needed to decide about the best breeding schemes to choose for tropical pig production.

International audience; Gut microbiota plays a central role in health and nutrient digestion and would help the host for better coping with environmental perturbations. In tropical conditions or in temperate countries during Summer, elevated ambient temperatures can cause economic losses to the pig industry. During heat stress (HS), the reduction in voluntary feed intake is the main adaptation response for reducing heat production. This lower feed intake has subsequent negative effects on pig performance. The main purpose of this study was to investigate the relationships between HS and gut microbiota composition. A better understanding of the microbiota response to HS could allow the selection for animals well adapted to HS. Genetically related pigs were raised under temperate or tropical farm conditions with mean thermal humidity indexes respectively 23 and 25.5 from 11 to 23 weeks of age. In temperate conditions, pigs were submitted to a 3-week HS challenge at 30 °C. Faecal samples were collected in all pigs at 23 weeks of age in both environments (n=1,200 samples) and at 26 weeks of age in the temperate environment (n=600). Therefore, it was possible to compare microbiota from pigs raised in a temperate environment, a tropical climate, and exposed to HS. Microbiota extracted from pigs under temperate and tropical climate had different compositions whereas pigs exposed to heat challenge or raised in tropical conditions tended to share a common microbiota. HS challenge drastically modified gut microbiota and the groups before and after the challenge could be predicted in a multilevel sparse partial least square discriminant analysis with 30 OTUs and a mean classification error rate of 14%. Our experiment suggests that microbiota can be used as biomarkers of HS exposition.

International audience

International audience

International audience; The aim of this study was to evaluate the effect of 2 climatic environments (temperate [TEMP] vs. tropical humid [TROP]) on production and thermoregulation traits in growing pigs. A backcross design involving Large White (LW; heat sensitive) and Creole (CR; heat tolerant) pigs was studied. The same 10 F-1 LW x CR boars were mated with related LW sows in each environment. A total of 1,298 backcross pigs (n = 634 pigs from 11 batches for the TEMP environment and n = 664 pigs from 12 batches for the TROP environment) were phenotyped on BW (every 15 d from wk 11 to 23 of age), voluntary feed intake (ADFI, from wk 11 to 23), backfat thickness (BFT; at wk 19 and 23), skin temperature (ST; at wk 19 and 23), and rectal temperature (RT; at wk 19, 21, and 23). The feed conversion ratio was computed for the whole test period (11 to 23 wk). The calculation of the temperature-humidity index showed an average difference of 2.4 degrees C between the TEMP and TROP environments. The ADG and ADFI were higher in the TEMP environment than in the TROP environment (834 vs. 754 g/d and 2.20 vs. 1.80 kg/d, respectively; P < 0.001). Body temperatures were higher in the TROP environment than in the TEMP environment (35.9 vs. 34.8 degrees C for ST and 39.5 vs. 39.3 degrees C for RT, respectively; P < 0.001). Most of the studied traits (i.e., BW, BFT, ADG, ADFI, and RT) were affected by sire family x environment interactions (P < 0.05), resulting in "robust" and "sensitive" families. Our results show a family dependency in the relationships between heat resistance and robustness, suggesting the possibility of finding genotypes with high production and low heat sensitivity. Further research is needed to confirm the genetic x environment interaction and to detect QTL related to heat tolerance.

Heat stress (HS) in pig production is a critical problem intemperate countries during summer but also in tropical areaswhere pig production dramatically increased over the past 2decades. Physiological and metabolic adjustments resultingfrom the thermoregulatory responses to HS have negative consequenceson pig productivity and health. The objectives of thisexperiment were to improve knowledge on the mechanismsunderlining heat tolerance by comparing thermoregulatoryresponses in 3 different pig genotypes (G). This experimentwas performed on a total of 36 castrated male pigs: 1 genotypesensitive to HS (Large White [LW]), 1 genotype tolerant toHS (Créole [CR]), and a cross between LW and CR pigs. Pigswere housed at 24°C for 10 d and thereafter at 32°C for 5 d.The temperature (T) transition from 24 to 32°C occurred on d0 at a constant rate of 2°C/h. Pigs had free access to water andfeed. Body T and respiratory rate were measured on d –7, –4,and –3 at 24°C and on d 1, 2, 3, 4, and 5 at 32°C. Eighteen pigs(6 per G) were slaughtered on d –2 (before the T transition) andon d 5. At slaughter, blood and 3 tissue samples (backfat [BF],longissimus dorsi [LD], and liver [LI]) were collected. A transcriptomeanalysis was performed on blood and tissues usinga semicustom 60K microarray (GPL16524). Blood hormonesand metabolites were also measured. The T × G interactionwas not significant (P > 0.05) for feed intake and thermoregulatoryresponses (except for skin T). Whatever the G, HS hada significant negative effect on voluntary feed intake (–200 g/don average). The T increase resulted in an increased rectal andskin T and respiratory rate within the first 24 to 72 h of exposureand in a subsequent recovery phase characterized bya rapid decrease of these thermoregulatory responses. Plasmaglucose, lactate, glycerol, and albumin concentrations weresignificantly reduced under HS but creatine concentration increasedat 32°C. Thyroid hormone (triiodothyronine and thyroxine)concentrations were reduced at 32°C. Irrespective tothe G, a considerable number of differentially expressed genes(false discovery rate < 0.05) were found by comparing blood(13,807), LD (6,261), BF (5,236), and LI (435) samples collectedat 24°C with those collected at 32°C. A first functionalanalysis revealed that most of the significantly differentiallyexpressed genes especially in BF and LD were involved in theregulation of the oxidative phosphorylation pathway.

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"Chantier qualité spécifique "Auteurs Externes" département de Génétique animale : uniquement liaison auteur au référentiel HR-Access "; il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : REPORT; The climate is changing and according to the recent estimates from the IPCC, the likelihood of heatwave events is expected to increase both in number and in intensity. Temperature is projected toincrease from 1.8 to 4.0°C from 1980-1999 to 2090-2099. Hence, heat stress-related costs in pigproduction will be amplified in the future, both in temperate areas (summer heat waves) and tropicalareas (hot and humid environment). Meanwhile, world pig production is moving rapidly to tropicaland subtropical regions reaching now more than 50% of the total production. The world developmentof pig production has been achieved through improvement of animal genetics and management intemperate countries. However, selection performed in optimally controlled conditions has increasedthe sensitivity of animals to high ambient temperature. Heat stressed pigs reduce their feed intakewhich impair their growth or reproduction performances. Management solutions are available toattenuate the effect of heat stress on pigs, such as environmental solutions (water or feedingmanagement). However, these solutions are technically and economically difficult to implement. Thegenetic selection for improving environmental adaptation in pig production is the most promising longterm option. The PigHeaT project aims 1) at identifying QTLs for heat adaptation, by examining directresponses to find genes involved in metabolic ways, indirect responses to find genes affecting growthor robustness to environmental variations, 2) at better understanding the physiological mechanismsunderlying heat adaptation. It will provide tools for improving breeding strategies to face theupcoming global warming, and knowledge to better comprehend the physiological reactions ofanimals submitted to short and long term heat stress. The PigHeaT project is based on originalbiological resources and original experimental facilities. The studied population will be a backcrossbetween Large White pigs, productive but poorly thermotolerant breed, and Creole pigs, lowproductive but highly thermotolerant breed. The progeny issued from this backcross will express allpossible levels of thermal tolerance and production performances when submitted to heat stress,depending on the alleles received from their parents. High throughput phenotyping, metabolomics onall the progeny, and transcriptomics on a subset of extreme pigs selected on thermal toleranceresponse, will be applied. It will allow to refine the phenotypes and to achieve a high level of accuracyin QTL detection in the frame of the PigHeaT project. Additionally, the design will benefit from theunique combination of experimental facilities available at INRA: the first part of the project will relyon the backcross population raised in the experimental facilities located in the West Indies(Guadeloupe, tropical environment). The concomitant production of the same population in theexperimental facilities available in temperate France (Charente Maritime) will allow the detection ofgenetic by environment (GxE) effects for the QTL detected in Guadeloupe. Moreover, a heat wavephenomenon will be systematically simulated in the temperate environment at the end of the growingperiod. 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 inheat stress responses. The respective use of the QTL and biological knowledge in further breedingstrategies will finally be considered.

14 Pág. Departamento de ​Mejora Genética Animal, Heat stress (HS) affects pig performance, health and welfare, resulting in a financial burden to the pig industry. Pigs have a limited number of functional sweat glands and their thermoregulatory mechanisms used to maintain body temperature, are challenged by HS to maintain body temperature. The genetic selection of genotypes tolerant to HS is a promising long-term (adaptation) option that could be combined with other measures at the production system level. This review summarizes the current knowledge on the genetics of thermoregulation in pigs. It also discusses the different phenotypes that can be used in genetic studies, as well as the variability in thermoregulation between pig breeds and the inheritance of traits related to thermoregulation. This review also considers on-going challenges to face for improving heat tolerance in pigs.