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International audience; We evaluated the economic and environmental impacts of strategies that incorporated selection for pig feed:gain and dietary optimization based on a single or multiple objectives tailored to meet the population’s nutritional requirements, with the goal to optimize sustainable farm feed efficiency. The economic and environmental features of the strategy were evaluated using life cycle assessment (LCA) and bio-economic models. An individual trait-based LCA model was applied to evaluate global warming potential (GWP), terrestrial acidification potential (AP), freshwater eutrophication potential (EP), and land occupation (LO) of the combined genetics and nutrition optimization to produce 1kg of live pig weighing 120kg at the farm gate. A parametric individual trait-based bio-economic model was developed and applied to determine the cost breakdown, revenue and profit to be gained from a 120kg live pig at the farm gate. Applying the combined genetics and nutrition optimization, the individual performance traits of pigs from two genetic lines with contrasted levels of feed efficiency were simulated with InraPorc in response to diets formulated for least cost, least environmental impacts, or minimum combination of cost and environmental impacts objectives, and accounting for the nutritional requirements of each line. Significant differences in the environmental impacts (P < 0.0001) and profit (P < 0.05) between lines predicted the same reference diet showed that selection for feed efficiency (residual feed intake, RFI) in pigs improves pig production sustainability. When pig responses were simulated with their line optimized diets, except for EP, all the line environmental impacts were less (P < 0.05) than with the reference diet. The high correlations of feed conversion ratio (FCR) with the environmental impacts (> 0.82) and the profit (< -0.88) in both lines underline the importance of feed efficiency as a lever for the sustainability of pig production systems. Implementing combined genetics and nutrition optimization, the inherent profit and environmental differences between the genetic lines was predicted to be reduced from 23.4% with the reference diet to 7.6% with the diet optimized jointly for economic and environmental objectives (joint diet). Consequently, for increased pig sustainability, diet optimization for sustainability objectives should be applied to cover the specific nutritional requirements arising in the herd from the pigs’ genetic level.

International audience; Purpose Use a holistic individual life cycle assessment (LCA) to investigate possible mitigation of environmental impacts through optimisation of overall farm feed efciency by combining animal selection for feed efciency and formulation of diets with minimum environmental impacts tailored to pig nutritional requirements.Methods A linear multi-objective optimisation method was used to combine diet optimisation tailored to meet the representative nutritional requirements of genetic lines with environmental optimisation of the environmental impacts of the diet. Environmental optimisation was obtained by weighting the environmental impacts of the diet in a single environmental impact score. An individual trait-based LCA model with a cradle-to-farm-gate system boundary and functional unit of 1 kg live pig at the farm gate was applied to genetic lines selected for high (LRFI, high feed efcient line) and low (HRFI, low feed efcient line) feed efciency data. The production traits of each individual animal in response to the optimised diets were simulated with InraPorc® and imported into the individual LCA model to assess global warming potential (GWP), terrestrial acidifcation potential (AP), freshwater eutrophication potential (EP), and land occupation (LO) of the overall farm feed efciency approach.Results and discussion Integrating selection for feed efciency, nutritional requirements of genetic lines (HRFI and LRFI) and environmental diet optimisation resulted in overall mitigation of environmental impacts. Compared to the conventional diet, the environmental score of the optimised tailored diets was reduced by 5.8% and 5.2% for LRFI and HRFI lines, respectively. At the general production system level, the environmental impacts decreased by an average of 4.2% for LRFI and 3.8% for HRFI lines compared to environmental impacts of the lines fed the conventional diet (P < 0.05). The HRFI line with its optimised tailored diet had fewer impacts than the LRFI line with the conventional diet, except for EP. Individual LCA revealed high correlations between environmental impacts and feed efciency and protein deposition traits.Conclusions Implementation of overall farm feed efciency would efectively mitigate environmental impacts. A holistic economic evaluation of the resulting trade-of between diet costs and pig performances is now needed

International audience; Hypothermia is a factor of piglet neonatal mortality. This study used Infra-Red Thermography (IRT) to assess thermoregulation abilities of piglets from two lines divergent for residual feed intake (RFI). At birth, body weight and rectal temperature were recorded from piglets of the 11th generation of the low RFI (LRFI, more efficient; n=34) and the high RFI (HRFI, less efficient; n=28). IRT images were taken at 8, 15, 30 and 60 min post-partum. Temperatures of the ear base and tip, and minimum, maximum and average temperatures of the back (i.e. shoulders to rumps) were extracted with Thermacam Researcher Pro 2.0, and analysed with linear mixed models (SAS 9.4). All temperatures increased overtime. The rectal temperature of piglets at birth was correlated with the initial temperature of the ear base and the maximum back temperature (0.36 and 0.35, respectively, P

Background Animal’s efficiency in converting feed into lean gain is a critical issue for the profitability of meat industries. This study aimed to describe shared and specific molecular responses in different tissues of pigs divergently selected over eight generations for residual feed intake (RFI). Results Pigs from the low RFI line had an improved gain-to-feed ratio during the test period and displayed higher leanness but similar adiposity when compared with pigs from the high RFI line at 132 days of age. Transcriptomics data were generated from longissimus muscle, liver and two adipose tissues using a porcine microarray and analyzed for the line effect (n = 24 pigs per line). The most apparent effect of the line was seen in muscle, whereas subcutaneous adipose tissue was the less affected tissue. Molecular data were analyzed by bioinformatics and subjected to multidimensional statistics to identify common biological processes across tissues and key genes participating to differences in the genetics of feed efficiency. Immune response, response to oxidative stress and protein metabolism were the main biological pathways shared by the four tissues that distinguished pigs from the low or high RFI lines. Many immune genes were under-expressed in the four tissues of the most efficient pigs. The main genes contributing to difference between pigs from the low vs high RFI lines were CD40, CTSC and NTN1. Different genes associated with energy use were modulated in a tissue-specific manner between the two lines. The gene expression program related to glycogen utilization was specifically up-regulated in muscle of pigs from the low RFI line (more efficient). Genes involved in fatty acid oxidation were down-regulated in muscle but were promoted in adipose tissues of the same pigs when compared with pigs from the high RFI line (less efficient). This underlined opposite line-associated strategies for energy use in skeletal muscle and adipose tissue. Genes related to cholesterol synthesis and efflux in liver and perirenal fat were also differentially regulated in pigs from the low vs high RFI lines. Conclusions Non-productive functions such as immunity, defense against pathogens and oxidative stress contribute likely to inter-individual variations in feed efficiency. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-3639-0) contains supplementary material, which is available to authorized users.

International audience; Selection for residual feed intake (RFI), which is used to select animals for feed efficiency, also influences nutrient partitioning between growth and maintenance functions. This study was designed to investigate if selection for reduced RFI can alter the trade-off between growth and immunity and contributes to differences in metabolic responses to an inflammatory challenge. Piglets from 2 lines divergently selected on RFI (low: RFI−, n = 10, and high: RFI+, n = 11) were challenged at 55 d of age (on d 0) with complete Freund’s adjuvant (CFA) to induce a noninfectious pneumonia. Plasma haptoglobin and nutrient concentrations (in fasted state and 2 h after feeding) were determined from d −1 to d 7, and tissue protein metabolism was determined on d 8. Haptoglobin concentrations were greater from d 1 to d 7 relative to d −1 (P < 0.01). Feed intake was less on d 1 than on the other days (P < 0.001), as was total AA plasma concentrations at fasted state (P < 0.05). Fasted concentrations of His (P = 0.06) and Trp (P = 0.05) tended to be less, those of Val were less (P < 0.05), and fed concentrations of Lys were increased (P < 0.05) on d 7 compared to d −1. Uremia was less on d 7 than on d −1 at fasted state (P < 0.05), whereas it did not vary at fed state (P > 0.1). Fasted glucose and insulin plasma concentrations were stable across days (P > 0.1). In the fed state and in only RFI+ pigs, glucose concentration was greater on d 1 than on d 3, 5, and 7 (P < 0.05). Total AA, Gln, Ile, Leu, Pro (P < 0.05), and hydroxyproline (P = 0.07) were less in RFI− than RFI+ pigs at fed state, whereas Ala and Gly were less in RFI− pigs at fasted and fed states (P < 0.05). Citrulline (P < 0.05) and Met (P < 0.01) concentrations were greater in RFI− than RFI+ pigs in the fasted state, whereas Asp was greater in RFI− pigs in both fasted and fed states (P < 0.05). On d 8, liver and LM protein synthesis tended to be lower (P = 0.07 and 0.09, respectively) and liver calpain activity was greater (P = 0.07) in RFI− than RFI+ pigs. Liver and LM proteasome did not differ between lines (P > 0.1). The metabolic differences between lines were not associated with differences in feed intake, ADG between d −1 and d 8, and haptoglobin concentration (P > 0.1). Thus, it seems that that, using different metabolic strategies, both lines coped similarly with the CFA challenge. Contrary to our hypothesis, this experiment showed, in young pigs, no advantage of RFI+ animals in response to an inflammatory challenge.

International audience; Performances of growing rabbits are determined by their genotype and their environment. The effect of maternal environment is particularly important in this species. Improvement of feed efficiency is essential to increase the competitiveness of the rabbit industry but also to reduce the animal excretion, and consequently decrease the environmental impact of the production. It can be achieved in rabbit by selection on residual feed intake (RFI) or on growth under restricted feeding (Drouilhet et al., 2013, 2015). However, these selection strategies do not take into account the contribution of gut microbiota to improved feed efficiency, although some previous results have demonstrated its relation with digestive efficiency in chicken (Mignon-Grasteau et al., 2015). To further investigate the effects of the animal genotype and maternal environment on feed efficiency, an experiment based on cross fostering between a line selected on RFI and a non-selected control line was performed. Ultimately, it should allow disentangling the effect of animal genetic and dam microbiota transmission on the traits. The objective of this preliminary study was to estimate both host genotype effect and maternal environment effect on growth and feed efficiency in rabbit.

International audience; Selection for residual feed intake (RFI), which is used to select animals for feed efficiency, also influences nutrient partitioning between growth and maintenance functions. This study was designed to investigate if selection for reduced RFI can alter the trade-off between growth and immunity and contributes to differences in metabolic responses to an inflammatory challenge. Piglets from 2 lines divergently selected on RFI (low: RFI−, n = 10, and high: RFI+, n = 11) were challenged at 55 d of age (on d 0) with complete Freund’s adjuvant (CFA) to induce a noninfectious pneumonia. Plasma haptoglobin and nutrient concentrations (in fasted state and 2 h after feeding) were determined from d −1 to d 7, and tissue protein metabolism was determined on d 8. Haptoglobin concentrations were greater from d 1 to d 7 relative to d −1 (P < 0.01). Feed intake was less on d 1 than on the other days (P < 0.001), as was total AA plasma concentrations at fasted state (P < 0.05). Fasted concentrations of His (P = 0.06) and Trp (P = 0.05) tended to be less, those of Val were less (P < 0.05), and fed concentrations of Lys were increased (P < 0.05) on d 7 compared to d −1. Uremia was less on d 7 than on d −1 at fasted state (P < 0.05), whereas it did not vary at fed state (P > 0.1). Fasted glucose and insulin plasma concentrations were stable across days (P > 0.1). In the fed state and in only RFI+ pigs, glucose concentration was greater on d 1 than on d 3, 5, and 7 (P < 0.05). Total AA, Gln, Ile, Leu, Pro (P < 0.05), and hydroxyproline (P = 0.07) were less in RFI− than RFI+ pigs at fed state, whereas Ala and Gly were less in RFI− pigs at fasted and fed states (P < 0.05). Citrulline (P < 0.05) and Met (P < 0.01) concentrations were greater in RFI− than RFI+ pigs in the fasted state, whereas Asp was greater in RFI− pigs in both fasted and fed states (P < 0.05). On d 8, liver and LM protein synthesis tended to be lower (P = 0.07 and 0.09, respectively) and liver calpain activity was greater (P = 0.07) in RFI− than RFI+ pigs. Liver and LM proteasome did not differ between lines (P > 0.1). The metabolic differences between lines were not associated with differences in feed intake, ADG between d −1 and d 8, and haptoglobin concentration (P > 0.1). Thus, it seems that that, using different metabolic strategies, both lines coped similarly with the CFA challenge. Contrary to our hypothesis, this experiment showed, in young pigs, no advantage of RFI+ animals in response to an inflammatory challenge.

National audience

Chantier qualité GA; Residual feed intake (RFI) has been explored as an alternative selection criterion to feed conversion ratio to capture the fraction of feed intake not explained by expected production and maintenance requirements. Selection experiments have found that low RFI in the growing pig is genetically correlated with reduced fatness and feed intake. Selection for feed conversion ratio also reduces sow appetite and fatness, which, together with increased prolificacy, has been seen as a hindrance for sow lifetime performance. The aims of our study were to derive equations for sow RFI during lactation (SRFI) and to evaluate the effect of selection for RFI during growth on sow traits during lactation. Data were obtained on 2 divergent lines selected for 7 generations for low and high RFI during growth in purebred Large Whites. The RFI was measured on candidates for selection (1,065 pigs), and sow performance data were available for 480 sows having from 1 to 3 parities (1,071 parities). Traits measured were sow daily feed intake (SDFI); sow BW and body composition before farrowing and at weaning (28.4 +/- 1.7d); number of piglets born total, born alive, and surviving at weaning; and litter weight, average piglet BW, and within-litter SD of piglet BW at birth, 21 d of age (when creep feeding was available), and weaning. Sow RFI was defined as the difference between observed SDFI and SDFI predicted for sow maintenance and production. Daily production requirements were quantified by litter size and daily litter BW gain as well as daily changes in sow body reserves. The SRFI represented 24% of the phenotypic variability of SDFI. Heritability estimates for RFI and SRFI were both 0.14. The genetic correlation between RFI and SRFI was 0.29 +/- 0.23. Genetic correlations of RFI with sow traits were low to moderate, consistent with responses to selection; selection for low RFI during growth reduced SDFI and increased number of piglets and litter growth, but also increased mobilization of body reserves. No effect on rebreeding performance was found. Metabolic changes previously observed during growth in response to selection might explain part of the better efficiency of the low-RFI sows, decreasing basal metabolism and favoring rapid allocation of resources to lactation. We propose to consider SRFI as an alternative to SDFI to select for efficient sows with reduced input demands during lactation.

Residual feed intake (RFI), defined as the difference between observed and predicted feed intakes, has been explored as a relevant selection criterion to improve feed efficiency in growing pigs. Previous studies exploring the genetic and physiological bases of RFI have been focused on pigs fed a regular diet. The aim of this study was to evaluate the effects of RFI selection on pigs' ability to digest and metabolize a diet enriched in fiber. After 11 wk of age, pigs of 2 lines divergently selected for RFI (low or high; n = 7 pairs of littermates in each line) were fed either a control diet (133 g NDF and 9.69 MJ NE/kg) or a high-fiber diet (244 g NDF and 8.36 MJ NE/kg) for 3 wk. Irrespective of diet, ADFI and water consumption were lower (P < 0.001) in the low RFI line, whereas G:F over the test period was 16% greater (P < 0.001) in that line compared with the high RFI line. There was no line-associated difference in the digestibility of nutrients and energy, despite a lighter digestive tract (-6.4%, P = 0.04) and a lower colon weight (-8.6%, P = 0.03) in the low RFI pigs than in the high RFI pigs. As compared with the control diet, ADFI was reduced (-7.5%, P < 0.001) in both lines when fed a high-fiber diet, but ADG and G:F were lowered for the high RFI line only (P < 0.05). The high-fiber diet decreased (P < 0.01) the digestibility values of nutrients and energy similarly in both lines. However, it increased the ratio of acetate to propionate concentrations in the distal part of the gastrointestinal tract for the high RFI line only (P < 0.07). The pattern of response of plasma metabolites and hormones to a meal test was altered by RFI selection, but it was not affected by the diet. The increase in glucose concentration after meal ingestion was more pronounced (P < 0.05) in the low RFI line, and long-lasting plasma concentrations of lactate tended to be lower (P < 0.10) in the low RFI line than in high RFI line. Plasma NEFA concentrations were greater in that line compared with the high RFI line. The activity levels of catabolic enzymes in muscle and the liver did not differ between lines and diets. In conclusion, the low RFI pigs seem to better utilize a high-fiber diet than high RFI pigs. This was not associated with marked changes in digestion, and the underlying metabolic mechanisms remain to be clarified.

The aim of the study was to evaluate the consequences of a divergent selection for residual feed intake (RFI) during growth in a temperate environment (TEMP) on sow performance in a tropical environment (TROP). Sows came from a selection experiment conducted at INRA in which 2 lines were selected for larger (RFI(+)) or smaller (RFI(─)) feed intake than predicted from performance. In the first analysis, a subsample of data obtained in TROP conditions (49 lactations) was compared to those obtained in TEMP on their sibs mated with the same boars (54 lactations). In the second analysis, data obtained in the TROP environment (82 lactations) were analyzed for testing the effect of season (warm vs. hot) and line on sow performance. Except for the lactation length, the interaction between line and climatic environment was not significant for the others traits (P > 0.05). The ADFI expressed per kilogram of litter BW gain tended to be higher in the RFI(+) line bred in the TROP environment (P = 0.080), together with piglet BW at weaning, which tended to be lower (P = 0.080). The ADFI was lower in TROP than in TEMP (4.56 vs. 5.86 kg/d; P = 0.003), with negative consequence on litter BW gain and maternal BW loss. The RFI(-) sows tended to eat less feed than RFI(+) sows during lactation (4.55 vs. 5.86 kg/d; P = 0.099). Litter BW at weaning was higher in the RFI(─) line. The RFI(─) sows ate significantly less feed to produce 1 kg of litter than the RFI(+) sows and tended to lose a larger amount of BW during lactation than the RFI(+) sows (2.40 vs. 3.02 kg/kg and -0.66 vs. -0.39 kg/d, respectively, P < 0.10). Whatever the line, ADFI was reduced by about 21% in the hot season (P < 0.05). Litter BW gain was depressed (P < 0.05) in the hot season (1.72 vs. 2.08 kg/d in the warm season; P = 0.023). Lactation maternal BW loss tended to increase in the hot season (1.10 vs. 0.71 kg/d in the warm season; P = 0.016), but back fat loss remained constant (P = 0.295). In the TROP environment, the amount of feed required to produce 1 kg of litter was not influenced by the line in the warm season (2.53 kg/kg on average; P = 0.99), but it tended to be lower in the RFI(─) line when compared to the RFI(+) line in the hot season (2.06 vs. 3.45 kg/kg; P = 0.050). This higher apparent efficiency in RFI(─) sows was mainly related to greater maternal body reserve mobilization (i.e., BW and back fat losses). In conclusion, selection for low RFI during growth in a TEMP environment did not impair sow and litter performance in tropical conditions.

Chantier qualité GA; Improvement of feed efficiency can be achieved by genetic selection directly on feed to BW gain ratio or for alternative traits. In the present study, 2 different traits were explored in the growing rabbit and their heritability and genetic correlations with traits recorded between weaning (30 d) and 63 d of age: i) residual feed intake (RFI), to select animals having low ad libitum feed intake independently from their production level, and ii) ADG under restricted feeding (ADGR; with a restriction level of 80% compared with ad libitum feeding of a control group), to select animals having high growth rate despite limited feed intake. To study these traits, 2 rabbit lines were established named i) ConsoResidual line and ii) ADGrestrict line. Under ad libitum or restricted feeding, it comes to select animals that waste less energy for maintenance, metabolism, or activity and retain more for tissue deposition. The selection process was similar in both lines. Data comprised records from generations 0 to 6 for about 1,800 rabbits per line measured for their BW at weaning and 63 d of age (BW63) and their individual feed consumption. Under ad libitum feeding, the heritability estimates were moderate for RFI (0.16 ± 0.05), ADG (0.19 ± 0.05), and feed conversion ratio (FCR; 0.22 ± 0.05). The high genetic correlation estimated between RFI and FCR (0.96 ± 0.03) was in accordance with the literature. The genetic correlation between RFI and ADG traits was not significant. Thus, selection for low RFI with ad libitum feeding was confirmed as a potential trait to improve FCR and reduce feed intake, with little effect on ADG. To our knowledge, there is no previous selection experiment on growing rabbits with restricted feeding. Our heritability estimates for ADGR and feed conversion ratio under restricted feeding (FCRR) were moderate (0.22 ± 0.06 and 0.23 ± 0.07, respectively) and had very high negative genetic correlation. Both selection criteria were found with high and favorable genetic correlations with feed efficiency recorded under each feeding regimen. However, their different genetic correlations with BW at weaning and at 63 d of age (BW63R; respectively, 0.85 and 0.17 for RFI and -0.25 and 0.81 for ADGR) suggested different impacts on major production traits that need further analyses to decipher the relative advantages of the 2 selection criteria, together with interactions between genotypes and feeding regimen.

Chantier qualité GA; Castrated males from 2 lines of purebred French Large White obtained from a divergent selection experiment for their residual feed intake (RFI) over 7 generations were measured for their energy utilization during thermal acclimation to increased ambient temperature. The RFI+ line consumed more feed than predicted from its performance, whereas the RFI− line consumed less feed. Each pig was exposed to 24°C for 7 d (P0) and thereafter to a constant temperature of 32°C for 3 consecutive periods of 7 d (P1, P2, P3). Feed intake, feeding behavior parameters, digestibility, components of heat production (HP; measured by indirect calorimetry in respiration chambers), and energy, nitrogen, fat, and water balance were measured in pigs offered feed and water ad libitum and individually housed in respiratory chambers. Two identical respiratory chambers were simultaneously used, and 5 pigs of each line were measured successively. Whatever the trait, the interaction between line and period was not significant (P > 0.10). On average, ADFI was greater in the RFI+ than in the RFI− line (1,945 vs. 1,639 g/d; P = 0.051) in relation to an increase of the mean size of each feeding bout (128 vs. 82 g/visit; P < 0.001). There was no line effect on nutrient and energy digestibility. Total HP tended to be greater in RFI+ than in RFI− lines (1,279 vs. 1,137 kJ*kg BW-0.60*d−1; P = 0.065), which tended to retain more energy (968 vs. 798 kJ*kg BW-0.60*d−1; P = 0.050). The sensible heat loss was greater in RFI+ compared with the RFI− line (644 vs. 560 kJ*kg BW-0.60*d−1; P = 0.020). The RFI+ pigs consumed more water (+981 vs. 657 g*kg BW-0.60*d−1; P = 0.085) and produced more urine (589 vs. 292 g*kg BW-0.60*d−1; P < 0.001) than RFI− pigs, whereas water evaporation was similar for both lines. On average, ME intake and HP declined by about 38% and 20%, respectively, from P0 to P1 (P < 0.001). In contrast to ME intake, HP gradually decreased (P < 0.05) from P1 to P3 in connection with a reduction of the activity related HP. The evaporative heat loss represented 30% on the total heat loss on P0, and this proportion significantly increased on P1 (61%; P < 0.001) and remained constant thereafter. In conclusion, our results suggest that thermal heat acclimation in pigs is mainly related to a biphasic reduction of HP rather than a change in the ability of losing heat, and it did not significantly differ between RFI+ and RFI− lines despite a decreased HP in the latter ones.

Chantier qualité GA; Previous selection experiments using residual feed intake (RFI) to select pigs with a high feed efficiency have reported that a low RFI was associated with a reduced body fat content and a greater muscle glycogen content. In the current study, growing Large White female piglets from 2 lines divergently selected for RFI were used to determine the changes in energy and protein metabolisms in key tissues and their cross talks in response to selection. Pigs of low RFI (RFI(-); n = 26) or high RFI (RFI(+); n = 36) selection lines were offered free access to feed during postweaning and growing periods. Pigs of each line were then slaughtered at 19 kg (n = 8 per line) or 115 kg BW (n = 14 to 18 per line). A third group of pigs of the RFI(+) line was offered feed at the same level per metabolic BW (BW0.60) as RFI- pigs (group RFI+R, n = 14). Regardless of the growth period considered, G:F was less in RFI(+) pigs than in RFI(-) pigs. At 19 kg BW, RFI(+) and RFI(-) pigs had a similar body composition and tissue lipid content. The fractional rate of protein synthesis and proteasome activity were decreased (P < 0.090) in the livers of RFI(+) pigs compared with RFI(-) pigs whereas activities of energy catabolic enzymes did not differ in the liver and LM samples. Plasma insulin was conversely greater (P = 0.049) in RFI(+) pigs at this stage. At 115 kg BW, enzyme activities of protein catabolism in the liver and in the LM did not differ (P > 0.10) between RFI(+) pigs and RFI(-) pigs. Both lactate dehydrogenase activity participating in glucose metabolism and hydroxylacylCoA dehydrogenase activity involved in fatty acid oxidation were greater (P < 0.05) in the liver and LM of RFI(+) pigs compared with RFI(-) pigs. In the liver, contrary to the LM, those differences in enzyme activities were directly associated with selection on RFI regardless of ADFI. Increased backfat depth and content and greater lipid content and adipocyte hypertrophy (P < 0.05) in subcutaneous adipose tissue were reported in RFI(+) pigs compared with RFI(-) pigs at 115 kg BW without marked changes in key lipogenic enzyme activities; these changes were directly associated with ADFI. In conclusion, the present study shows an increase of catabolic pathway activities in the liver and muscle of RFI(+) pigs at market weight that is likely to generate more ATP compared with RFI(-) pigs.

Residual feed intake (RFI) is defined as the difference between the observed feed intake and that expected based on requirements for maintenance and production. A divergent selection was conducted during 4 generations in Large White male pigs to produce low and high RFI lines. The present study aims at determining the influence of this selection on biochemical and histological traits of skeletal muscle, and relating these changes to correlated effects on growth, carcass composition, and meat quality traits. At 8 d preslaughter, biopsies from the LM were taken in the fed state on 14 females from each RFI line fed ad libitum. Animals were slaughtered at 107.8 ± 8.0 kg of BW without any previous fasting. Samples of LM, semimembranosus (SM), biceps femoris (BFM), and rhomboideus muscles were taken at both 30 min and 24 h postmortem. Myofiber typing was only assessed in LM. Low RFI pigs (“efficient”) had leaner carcasses with greater muscle content (P < 0.001), less backfat thickness (P < 0.001), and less intramuscular fat content in all 4 muscles (P < 0.01 to P = 0.04). Their greater muscle content was associated with hypertrophy of all fast-twitch fibers. Glycogen content in all glycolytic muscles (i.e., LM, SM and BFM), was greater in low than high RFI pigs. The greater accumulation of glycogen in LM of low RFI pigs was specifically located in the fast-twitch glycolytic IIBW fibers, which correspond to fibers containing IIb, IIb + IIx, or IIx myosin heavy chains. The difference in muscle glycogen content between RFI line pigs was more significant in the living animals (P = 0.0003) than at 30 min postmortem (P = 0.08). This was associated with a decreased ultimate pH (P = 0.001), and greater lightness of color (P = 0.002) and drip loss (P = 0.04) in LM of low than high RFI line pigs, suggesting that selection for reduced RFI may impair some meat quality traits, such as water-holding capacity. Pigs from the low RFI line exhibited a greater (P = 0.02) percentage of IIBW fibers in LM and tended (P < 0.10) to have less lipid β-oxidative capacity in LM, SM, and BFM. In contrast, no difference (P > 0.10) between lines was found for citrate synthase and lactate dehydrogenase activities, mitochondrial activity, and expression of genes coding for uncoupling proteins 2 and 3. Differences between RFI pigs in plasma leptin, cortisol, and thyroid hormone concentrations are presented and discussed. In conclusion, selection for low RFI influenced muscle properties in a way favoring muscle mass, but likely impairing meat quality.

Residual feed intake (RFI) is defined as the difference between the observed feed intake and that expected based on requirements for maintenance and production. A divergent selection was conducted during 4 generations in Large White male pigs to produce low and high RFI lines. The present study aims at determining the influence of this selection on biochemical and histological traits of skeletal muscle, and relating these changes to correlated effects on growth, carcass composition, and meat quality traits. At 8 d preslaughter, biopsies from the LM were taken in the fed state on 14 females from each RFI line fed ad libitum. Animals were slaughtered at 107.8 ± 8.0 kg of BW without any previous fasting. Samples of LM, semimembranosus (SM), biceps femoris (BFM), and rhomboideus muscles were taken at both 30 min and 24 h postmortem. Myofiber typing was only assessed in LM. Low RFI pigs ("efficient") had leaner carcasses with greater muscle content (P < 0.001), less backfat thickness (P < 0.001), and less intramuscular fat content in all 4 muscles (P < 0.01 to P = 0.04). Their greater muscle content was associated with hypertrophy of all fast-twitch fibers. Glycogen content in all glycolytic muscles (i.e., LM, SM and BFM), was greater in low than high RFI pigs. The greater accumulation of glycogen in LM of low RFI pigs was specifically located in the fast-twitch glycolytic IIBW fibers, which correspond to fibers containing IIb, IIb + IIx, or IIx myosin heavy chains. The difference in muscle glycogen content between RFI line pigs was more significant in the living animals (P = 0.0003) than at 30 min postmortem (P = 0.08). This was associated with a decreased ultimate pH (P = 0.001), and greater lightness of color (P = 0.002) and drip loss (P = 0.04) in LM of low than high RFI line pigs, suggesting that selection for reduced RFI may impair some meat quality traits, such as water-holding capacity. Pigs from the low RFI line exhibited a greater (P = 0.02) percentage of IIBW fibers in LM and tended (P < 0.10) to have less lipid β-oxidative capacity in LM, SM, and BFM. In contrast, no difference (P > 0.10) between lines was found for citrate synthase and lactate dehydrogenase activities, mitochondrial activity, and expression of genes coding for uncoupling proteins 2 and 3. Differences between RFI pigs in plasma leptin, cortisol, and thyroid hormone concentrations are presented and discussed. In conclusion, selection for low RFI influenced muscle properties in a way favoring muscle mass, but likely impairing meat quality.

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Genetic selection on residual feed intake (RFI) can be used as an alternative method to G: F to improve feed efficiency in pigs. The objective of this study was to determine the effects of selection for RFI on digestive and metabolic utilization of energy in 2 lines of purebred French Large White castrated male pigs obtained from a divergent selection experiment over 6 generations. The RFI(+) (high RFI) line consumed more feed than predicted from performance compared with the RFI(-) (low RFI) line. Digestibility of energy and nutrients, total heat production (HP), HP related to physical activity, and energy and N balance were measured in respiration chambers for a 6-d period in pigs offered feed ad libitum. Pigs remained in the chamber for an additional day and did not receive any feed to estimate the fasting HP and calculate the thermic effect of feeding. Five pairs of 2 littermates from the same farrowing batch were used in each line. Because 2 respiration chambers were available for the trial, pigs were measured regularly during the 25- to 95-kg growing period. Two pigs per chamber were used until pigs reached 45 kg of BW, and 1 pig per chamber was used thereafter. Individual feed intake and BW gain were measured continuously from weaning to the end of the trial. Pigs were fed 3 diets with decreasing CP contents during the 25 to 45 (period 1), 45 to 65 (period 2), and 65 to 95 (period 3) kg of BW periods. Average daily feed intake was greater in RFI(+) pigs than in RFI(-) pigs between 25 and 65 kg of BW (2,128 vs. 1,891 g/d; P < 0.01) and G: F was 8% greater in RFI(-) pigs compared with RFI(+) pigs (P < 0.01). There was no line effect on digestibility coefficients or N retention, irrespective of the experimental period studied. Nitrogen retention was 31.2, 28.7, and 20.8 g/d at periods 1, 2, and 3, respectively (P < 0.001). The HP was greater in RFI(+) pigs than in RFI(-) pigs (1,497 vs. 1,383 kJ.kg of BW(-0.60).d(-1); P < 0.01), with no subsequent line effect on energy retention. The activity-related HP tended to be greater in RFI(+) pigs than in RFI(-) pigs (250 vs. 218 kJ.kg of BW(-0.60).d(-1); P = 0.09), and the fasting HP was 10% greater (P = 0.04) in RFI(+) pigs than in RFI(-) pigs (846 vs. 771 kJ.kg of BW(-0.60).d(-1)). The thermic effect of feeding, expressed as a percentage of ME intake, was the same for both lines of pigs (average, 14.7%). In conclusion, the RFI(+) pigs are energetically less efficient because of their greater HP related to physical activity and basal metabolic rate.

Chantier qualité GA; Genetic selection on residual feed intake (RFI) can be used as an alternative method to G: F to improve feed efficiency in pigs. The objective of this study was to determine the effects of selection for RFI on digestive and metabolic utilization of energy in 2 lines of purebred French Large White castrated male pigs obtained from a divergent selection experiment over 6 generations. The RFI(+) (high RFI) line consumed more feed than predicted from performance compared with the RFI(-) (low RFI) line. Digestibility of energy and nutrients, total heat production (HP), HP related to physical activity, and energy and N balance were measured in respiration chambers for a 6-d period in pigs offered feed ad libitum. Pigs remained in the chamber for an additional day and did not receive any feed to estimate the fasting HP and calculate the thermic effect of feeding. Five pairs of 2 littermates from the same farrowing batch were used in each line. Because 2 respiration chambers were available for the trial, pigs were measured regularly during the 25- to 95-kg growing period. Two pigs per chamber were used until pigs reached 45 kg of BW, and 1 pig per chamber was used thereafter. Individual feed intake and BW gain were measured continuously from weaning to the end of the trial. Pigs were fed 3 diets with decreasing CP contents during the 25 to 45 (period 1), 45 to 65 (period 2), and 65 to 95 (period 3) kg of BW periods. Average daily feed intake was greater in RFI(+) pigs than in RFI(-) pigs between 25 and 65 kg of BW (2,128 vs. 1,891 g/d; P < 0.01) and G: F was 8% greater in RFI(-) pigs compared with RFI(+) pigs (P < 0.01). There was no line effect on digestibility coefficients or N retention, irrespective of the experimental period studied. Nitrogen retention was 31.2, 28.7, and 20.8 g/d at periods 1, 2, and 3, respectively (P < 0.001). The HP was greater in RFI(+) pigs than in RFI(-) pigs (1,497 vs. 1,383 kJ.kg of BW(-0.60).d(-1); P < 0.01), with no subsequent line effect on energy retention. The activity-related HP tended to be greater in RFI(+) pigs than in RFI(-) pigs (250 vs. 218 kJ.kg of BW(-0.60).d(-1); P = 0.09), and the fasting HP was 10% greater (P = 0.04) in RFI(+) pigs than in RFI(-) pigs (846 vs. 771 kJ.kg of BW(-0.60).d(-1)). The thermic effect of feeding, expressed as a percentage of ME intake, was the same for both lines of pigs (average, 14.7%). In conclusion, the RFI(+) pigs are energetically less efficient because of their greater HP related to physical activity and basal metabolic rate.

International audience

The main objective of the thesis was to investigate how genomic tools applied to the animal and its microbiota can contribute to improving selection for feed efficiency in pigs. The thesis relied on data from two pig lines from 10 generations of divergent selection for feed efficiency. Together with phenotypic records for about 200 pigs per line in all generations, 588 feces samples from generations 9 and 10 were collected. In addition, SNP genotyping data for about 1000 animals per line were available. Five traits were investigated: residual feed intake, feed conversion ratio, daily feed intake, average daily gain and backfat thickness. Throughout the thesis, we showed that molecular information acquired on the pigs or their microbiota could improve selection for feed efficiency. This trait is costly to record, whereas molecular information could be easier to obtain on a large number of pigs. In this project, the potential of genomic tools applied to pigs was examined in the second chapter, and it was explored in the two subsequent ones for the gut microbiota. We then first showed that when data availability is limited, genomic prediction using a training set combining animals from genetically related lines can be as accurate as genomic prediction using a training set from the target population only. Based on numerous scenario comparisons, our results provided insights into the design of reference populations to initiate genomic selection in livestock lines with small population size, do not have a large number of historical samples or data, and are developed simultaneously, as can be encountered in poultry and pig breeding, as well as in other crossbreeding schemes. Further studies would be needed to assess the economic potential of this approach and clarify the optimum balance between genotyping and phenotyping efforts. In the following chapters, we showed that the gut microbiota variability, captured via partial 16S rRNA gene sequencing, contributes to the variability of production traits, in particular feed efficiency traits. First, we identified microbiota components (genera, OTU, α-diversity indexes) with significant heritability (48 genera out of the 75 analysed, plus two α-diversity indexes). Twenty-one of these genera, belonging to the Lachnospiraceae, Ruminococcaceae, Prevotellaceae, Lactobacillaceae, Streptococcaceae, Rikenellaceae and Desulfovibrionaceae families, and the two α- diversity indexes were genetically correlated with some of the traits. Second, the study of the microbiability showed a substantial contribution of the microbial effects on the variability of feed efficiency traits (> 10%) and negligible contribution for other traits (, L'objectif principal de la thèse était d'étudier comment les informations génomiques de l'animal et de son microbiote peuvent contribuer à améliorer la sélection pour l'efficacité alimentaire chez le porc. La thèse s'est appuyée sur les données de deux lignées de porcs issues de 10 générations de sélection divergente pour l'efficacité alimentaire. En plus de phénotypes enregistrés pour environ 200 porcs par lignée et par génération, 588 échantillons de fèces ont été collectés en générations 9 et 10. De plus, des génotypes pour environ 1000 animaux par lignée étaient disponibles. Cinq caractères ont été étudiés: la consommation moyenne journalière résiduelle, l’indice de consommation, la consommation moyenne journalière, le gain moyen quotidien et l'épaisseur de lard dorsal. Dans cette thèse, nous avons montré que les informations moléculaires sur les porcs ou leur microbiote peuvent améliorer la sélection pour l'efficacité alimentaire. Ce caractère est coûteux à enregistrer, alors que les informations moléculaires pourraient être plus faciles à obtenir sur un grand nombre de porcs. Dans ce projet, le potentiel du génotypage des animaux a été examiné dans le premier chapitre, et celui du microbiote intestinal a été exploré dans les deux suivants. Nous avons d'abord montré que lorsque la disponibilité des données est limitée, la prédiction génomique avec une population de référence combinant des animaux de lignées génétiquement liées peut être aussi précise qu’une prédiction génomique utilisant une population de référence de la lignée cible uniquement. Comparant de nombreux scénarios, nos résultats ont fourni des repères pour la construction de populations de référence pour initier la sélection génomique dans des lignées petites, qui ne disposent pas d'un grand nombre d'échantillons ou de données historiques et sont développées simultanément. Cette situation peut être rencontrée en volaille et en porc ainsi que dans d'autres populations en croisement. Des études complémentaires seront nécessaires pour quantifier le potentiel économique de cette approche et clarifier l'équilibre optimal entre génotypage et de phénotypage. Dans les chapitres suivants, nous avons montré que la variabilité du microbiote intestinal, captée par séquençage partiel du gène de l'ARNr 16S, contribue à la variabilité des caractères de production, en particulier de l'efficacité alimentaire. Dans un premier temps, nous avons identifié des composantes du microbiote (genres, OTU, indices de -diversité) héritables (48 genres sur les 75 analysés, plus deux indices de -diversité). Vingt et un de ces genres, appartenant aux familles Lachnospiraceae, Ruminococcaceae, Prevotellaceae, Lactobacillaceae, Streptococcaceae, Rikenellaceae et Desulfovibrionaceae, et les deux indices de -diversité étaient génétiquement corrélés à certains caractères. Deuxièmement, l'étude de la microbiabilité a montré une contribution substantielle des effets microbiote à la variabilité de l'efficacité alimentaire (> 10%) et une contribution négligeable pour les autres caractères (< 5%). De plus, cette étude a révélé que la génétique de l'hôte avait une contribution plus élevée que le microbiote à la variance des caractères étudiés (héritabilité plus élevée que les valeurs de microbiabilité). Cette dernière étude a également montré des associations significatives de certains taxons microbiens avec les performances. Ces résultats ont souligné la possibilité d'utiliser certains caractères microbiens comme marqueurs pour la sélection de l'efficacité alimentaire chez les porcs. Des études complémentaires seront nécessaires pour évaluer comment les informations génomiques de l'hôte et du microbiote peuvent être combinées dans des modèles de prédiction pour soit mieux prédire les valeurs génétiques elles- mêmes, soit même obtenir des prédictions conjointes des valeurs génétiques et microbiote, qui conduiraient à la sélection de l'hologénome pour une efficacité de production améliorée.