Composition and quality characteristics of carcasses from pigs divergently selected for residual feed intake on high- or low-energy diets

Multi-omics reveal the effects and regulatory mechanism of dietary neutral detergent fiber supplementation on carcass characteristics, amino acid profiles, and meat quality of finishing pigs

This study aimed to reveal the effects and regulatory mechanism of dietary NDF on the performance of pigs by multi-omics analysis. Results showed that 16 % dietary NDF significantly improved meat quality, increased flavor amino acid content, and reduced backfat thickness and the feed-to-gain ratio. 16S rDNA sequencing showed that 16 % NDF significantly increased the abundance of Akkermansia, Lachnoclostridium, and Ruminococcus. Transcript analysis showed that genes related to muscle development and lipid metabolism were significantly modified. Metabonomic analysis showed that 16 % NDF significantly increased amino and fatty acid related metabolites. Correlation analysis suggested that 16 % NDF treatment may alter the gut microbiota and metabolites, regulate the expression of genes related to lipid and amino metabolism, and ultimately affect the flavor and performance of pigs. This study provides a novel understanding about the effect and regulatory mechanism of NDF supplements on the finishing pigs and a relevant reference for the improvement of diet formulation.

Pork carcass composition, meat and belly qualities as influenced by feed efficiency selection in replacement boars from Large White sire and dam lines

This study evaluated carcass attributes, meat and belly qualities in finisher boars (n = 79) selected for feed efficiency (low, intermediate and high) based on estimated breeding value for feed conversion ratio within a Large White dam and sire genetic lines. The sire line had lower trimmed fat proportions and higher lean than the dam line (P < 0.01). Genetic lines expressed slight colour changes and drip losses (P < 0.05), with no differences in pH, marbling and cooking traits (P > 0.05). High-efficient animals presented the highest lean yield (P < 0.01), the lowest trimmed fat proportion (P < 0.01) and no effect on meat and belly quality attributes (P > 0.05) compared with other efficient groups. Interaction between efficiency group and genetic line was only detected for belly weight and thickness (P < 0.01). High-efficient animals offer a greater leanness level, with minimal impact on meat and belly quality traits.

Sire-feed interactions for fattening performance and meat quality traits in growing-finishing pigs under a conventional and an organic feeding regimen

In a two-factorial feeding trial 120 growing-finishing pigs from eleven sires were fed on an organic (ORG) or a conventional (CON) diet. Diet ORG contained mainly oil press cakes and legume grains as protein source containing higher protein and crude fiber content along with slight deficiencies of limiting amino acids. Pigs were allocated to treatments balanced according to litter, sex and initial weight. Feed was offered ad libitum. Feed consumption, weight gain as well as carcass, meat and fat quality traits were recorded. ORG fed animals had lower weight gain, poorer feed conversion, lower loin muscle area, higher intramuscular fat content, higher ultimate pH (loin, ham), and a higher PUFA content in backfat. Despite for cook loss and dressing percentage, no sire-feed interactions were found. This indicates no need for a performance test, specifically designed for organic production. However, weight of the breeding values for the various traits and selection criteria should be adapted to the needs of organic production.

Nutritional approaches to slow late finishing pig growth: implications on carcass composition and pork quality

Although pork producers typically aim to optimize growth rates, occasionally it is necessary to slow growth, such as when harvest facility capacity is limited. In finishing pigs, numerous dietary strategies can be used to slow growth so pigs are at optimal slaughter body weights when harvest facility capacity and/or access is restored. However, the impact of these diets on pork carcass quality is largely unknown. Thus, this study aimed to evaluate the efficacy of dietary strategies to slow growth in late finishing pigs and evaluate their effects on carcass composition and pork quality. Mixed-sex pigs (n = 897; 125 ± 2 kg BW) were randomly allotted across 48 pens and assigned to 1 of 6 dietary treatments (n = 8 pens/treatment): (1) Control diet representative of a typical finisher diet (CON); (2) diet containing 3% calcium chloride (CaCl2); (3) diet containing 97% corn and no soybean meal (Corn); (4) diet deficient in isoleucine (LowIle); (5) diet containing 15% neutral detergent fiber (NDF) from soybean hulls (15% NDF); and (6) diet containing 20% NDF from soybean hulls (20% NDF). Over 42 d, pen body weights and feed disappearance were collected. Pigs were harvested in 3 groups (14, 28, and 42 d on feed) and carcass data collected. From the harvest group, 1 loin was collected from 120 randomly selected carcasses (20 loins/treatment) to evaluate pork quality traits. Overall, ADG was reduced in CaCl2, Corn, and 20% NDF pigs compared with CON pigs (P < 0.001). However, ADFI was only reduced in CaCl2 and 20% NDF pigs compared with CON (P < 0.001). Feed efficiency was reduced in CaCl2 and Corn pigs compared with CON (P < 0.001). Hot carcass weights were reduced in CaCl2 pigs at all harvest dates (P < 0.001) and were reduced in Corn and 20% NDF pigs at days 28 and 42 compared with CON pigs (P < 0.001). In general, CaCl2 and 20% NDF diets resulted in leaner carcasses, whereas the Corn diet increased backfat by 42 d on test (P < 0.05). Loin pH was reduced and star probe increased in CaCl2 pigs compared with CON pigs (P < 0.05); no treatments differed from CON pigs regarding drip loss, cook loss, color, firmness, or marbling (P ≥ 0.117). Overall, these data indicate that several dietary strategies can slow finishing pig growth without evidence of behavioral vices. However, changes to carcass composition and quality were also observed, indicating quality should be taken into consideration when choosing diets to slow growth.

Impact of a high-fibre diet on genetic parameters of production traits in growing pigs

The use of diets with increased fibre content from alternative feedstuffs less digestible for pigs is a solution considered to limit the impact of increased feed costs on pig production. This study aimed at determining the impact of an alternative diet on genetic parameters for growth, feed efficiency, carcass composition and meat quality traits. A total of 783 Large White pigs were fed a high-fibre (HF) diet and 880 of their sibs were fed a conventional (CO) cereal-based diet. Individual daily feed intake, average daily gain, feed conversion ratio and residual feed intake were recorded as well as lean meat percentage (LMP), carcass yield (CY) and meat quality traits. Pigs fed the CO diet had better performances for growth and feed efficiency than pigs fed the HF diet. They also had lower LMP and higher CY. In addition, pigs fed the CO diet had lower loin percentage and ham percentage and higher backfat percentage. No differences were observed in meat quality traits between diets, except for a* and b* values. For all traits, the genetic variances and heritability were not different between diets. Genetic correlations for traits between diets ranged between 0.80 ± 0.13 and 0.99 ± not estimable, and none were significantly different from 0.99, except for LMP. Thus, traits in both diets were considered as mainly affected by similar sets of genes in the two diets. A genetic correlation lower than 0.80 would justify redesigning the breeding scheme; however, some genetic correlations did not differ significantly from 0.80 either. Therefore, larger populations are needed for a more definitive answer regarding the design of the breeding scheme. To further evaluate selection strategies, a production index was computed within diets for the 29 sires with estimated breeding value reliability higher than 0.35. The rank correlation between indices estimated in the CO and in the HF diet was 0.72. Altogether, we concluded that limited interaction between feed and genetics could be evidenced, and based on these results there is no need to change pig selection schemes to adapt to the future increased use of alternative feedstuffs in production farms.

Effect of a dual enteric and respiratory pathogen challenge on swine growth, efficiency, carcass composition, and pork quality1

The objective of this study was to determine the influence of a dual respiratory and enteric pathogen challenge on growth performance, carcass composition, and pork quality of high and low feed efficient pigs. Pigs divergently selected for low and high residual feed intake (RFI, ~68 kg) from the 11th generation of Iowa State University RFI project were used to represent high and low feed efficiency. To elicit a dual pathogen challenge, half of the pigs (n = 12/line) were inoculated with Mycoplasma hyopneumoniae (Mh) and Lawsonia intracellularis (MhLI) on days post-inoculation (dpi) 0. Pigs in a separate room of the barn were not inoculated and used as controls (n = 12/RFI line). Pigs were weighed and feed intake was recorded to calculate ADG, ADFI, and G:F for the acclimation period (period 1: dpi -21 to 0), during peak infection (period 2: dpi 0 to 42), and during the remaining growth period to reach market weight (period 3: dpi 42 to harvest). At ~125 kg, pigs were harvested using standard commercial procedures. Carcasses were evaluated for composition (weight, fat free lean, loin eye area, 10th rib fat depth) and meat quality (pH decline, temperature decline, Hunter L, a, and b, subjective color and marbling, star probe, drip loss, cook loss, proximate composition, and desmin degradation). Challenged pigs had lesser ADFI than controls during period 2 (P < 0.05), but had greater ADG and G:F during period 3 (P < 0.05). Selection for feed efficiency did not result in a differential response to MhLI (P > 0.05). Loin chops from the less feed efficient, high RFI pigs, had greater drip loss, greater cook loss, lesser moisture content, greater Hunter L values, and greater Hunter b values (P < 0.05) than loin chops from low RFI pigs. Infection status did not significantly affect carcass composition or pork quality traits (P > 0.05). These results indicate that a MhLI challenge early in growth did not significantly affect ultimate carcass composition or meat quality traits. Selection for greater feed efficiency in pigs did not affect their response to pathogenic challenge.

Influence of postmortem aging and post-aging freezing on pork loin quality attributes

The objectives were to determine 1) the interaction between aging duration and post-aging freezing on pork loin quality attributes and 2) the relationship between pork loin star probe (SP) and Warner-Bratzler shear force (WBS). Loins from 20 carcasses were collected 1 d postmortem. Chops (n = 9; 2.54-cm thick) were fabricated from each loin and vacuum packaged. Four chops from each loin were aged at 4°C for 1, 8, 14, and 21 d and immediately evaluated (Fresh). Four adjacent chops were aged (1, 8, 14, and 21 d), frozen for 14 d, and thawed for evaluation (Frozen). An additional chop was used for evaluation of sarcomere length, intact desmin, and troponin-T degradation. Purge, objective color, pH, subjective color and marbling score, cook loss, SP, and WBS were evaluated at each aging period. Desmin and troponin-T degradation, and sarcomere length were measured on fresh samples at each day of aging. Post-aging freezing had no significant impact on SP, WBS, pH, and subjective color or marbling score at any aging period. Fresh chop purge increased at each day of aging (P < 0.01). Post-aging freezing resulted in greater purge at 1, 8, and 14 d aging (P < 0.01). Fresh chop cook loss was greater than post-aging freezing chop cook loss at 14 and 21 d aging (P < 0.05). Across all aging periods and treatments, SP was correlated (r = 0.85; P < 0.01) with WBS. Fresh chop SP and WBS decreased from 1 to 8 d aging but was not different after 8 d aging. The abundance of intact desmin decreased (P < 0.01) between 1, 8, and 14 d aging. Troponin-T degradation increased (P < 0.01) with each aging period. Sarcomere length was not different across aging periods (P > 0.05). Aging, without freezing, for 14 or 21 d did not improve SP or WBS observed at 8 d, corresponding with changes in desmin degradation.

Effect of lower-energy, higher-fiber diets on pigs divergently selected for residual feed intake when fed higher-energy, lower-fiber diets

Residual feed intake (RFI) is the difference between observed and predicted feed intake of an animal, based on growth and maintenance requirements. In Yorkshire pigs, divergent selection for increased (Low RFI) and decreased (High RFI) RFI was carried out over 10 generations (G) while feeding a corn- and soybean-meal-based, higher-energy, lower-fiber (HELF) diet. In G8 to G10, representing 4 replicates, barrows and gilts (n = 649) of the RFI lines were fed the HELF diet and a diet incorporating coproducts that were lower in energy and higher in dietary fiber (LEHF). The diets differed in ME, 3.32 vs. 2.87 Mcal/kg, and in neutral detergent fiber (NDF), 9.4% vs. 25.9%, respectively. The impact of the LEHF diet on 1) performance and growth, 2) diet digestibility, 3) genetic parameter estimates, and 4) responses to selection for RFI, when fed the HELF, was assessed. In general, the LEHF diet reduced the performance of both lines. When fed the HELF diet, the Low RFI pigs had lower (P < 0.05) ADFI (-12%), energy intake (-12%), ADG (-6%), and backfat depth (-12%); similar (P > 0.05) loin muscle area (LMA; +5%); and greater (P < 0.05) feed efficiency (i.e., 8% higher G:F and 7% lower RFI) than the High RFI line. These patterns of line differences were still present under the LEHF diet but differences for ADFI (-11%), energy intake (-10%), G:F (+2%), and RFI (-6%) were reduced compared to the HELF diet. Apparent total tract digestibility (ATTD) of the HELF and LEHF diets was assessed using 116 barrows and gilts from G8. When fed the HELF diet, ATTD of DM, GE, N, and NDF were similar between lines (P ≥ 0.27), but when fed the LEHF diet, the Low RFI pigs had greater digestibility (7%, 7%, 10%, and 32%) than the High RFI line (P ≤ 0.04). To measure responses to selection for RFI and estimate genetic parameters, data from all 10 generations were used (HELF; n = 2,310; LEHF, n = 317). Heritability estimates of performance traits ranged from 0.19 to 0.63, and genetic correlations of traits between diets were high and positive, ranging from 0.87 (RFI) to 0.99 (LMA). By G10, RFI in the Low RFI line was 3.86 and 1.50 genetic SD lower than in the High RFI line when fed the HELF and LEHF diets, respectively. Taken together, the results of this study demonstrate that responses to selection for RFI when fed a HELF diet are not fully realized when pigs are fed an extremely LEHF diet. Thus, feeding diets that differ from those used for selection may not maximize genetic potential for feed efficiency.

Porcine Reproductive and Respiratory Syndrome virus reduces feed efficiency, digestibility, and lean tissue accretion in grow-finish pigs

Porcine reproductive and respiratory syndrome (PRRS) virus is a major swine virus that causes reproductive impairment in sows, as well as respiratory disease, reduction in growth rates, and mortalities in all ages of pigs. The objective of this study was to quantify the impact PRRS has on grower-finisher pig feed efficiency and tissue accretion rates. Thirty PRRS naïve, littermate pairs of maternal line Choice Genetics gilts (33.6 ± 0.58 kg BW) were selected and pairs split across 2 barns consisting of 5 pens (n = 6 pigs/pen per barn). Pigs in both barns were fed corn-soybean-DDGS diets ad libitum. All pigs in one barn were inoculated (CHAL) via an i.m. injection of a live PRRS strain isolated from the region (0 d post inoculation, dpi), while pigs in the other barn were given a saline control injection (CONT). Pig performance (ADG, ADFI, G:F) was assessed from 35 kg BW until each group reached market BW (128 kg). Additionally, longitudinal apparent total tract digestibility (ATTD) and body composition was assessed using Dual-energy X-ray absorptiometry (DXA) post inoculation (dpi) to estimate lean, protein, fat and bone accretion rates. Serological data from CHAL pigs showed that PRRS titers peaked 7 dpi and these pigs seroconverted by 35 dpi. According to both genomic and protein PRRS titers, CONT pigs were naïve to CHAL throughout the study. The PRRS infection reduced (P < 0.001) ATTD of dry matter, energy and nitrogen by 3 to 5% at 21 dpi and the reduction in ATTD persisted after 65 dpi. Compared to the CONT, CHAL pigs had decreased ADG (0.89 vs. 0.80 kg/d, P < 0.001), ADFI (2.05 vs. 1.93 kg/d, P < 0.001), and G:F (0.44 vs. 0.41 kg/d, P < 0.001) over the entire test period. The CHAL pigs also had attenuated DXA predicted whole body accretion of lean (547 vs. 633 g/d, P = 0.001), protein (109 vs. 126 g/d, P = 0.001) and fat (169 vs. 205 g/d, P = 0.001) compared to their CONT counterparts from dpi 0 to 80. Based on carcass data at slaughter (and consistent with the DXA data), CHAL pigs had leaner carcasses and reduced yields. These data clearly demonstrate that PRRS infection reduces digestibility, feed efficiency and protein accretion rates in grower-finisher pigs.

Postmortem protein degradation is a key contributor to fresh pork loin tenderness

The objective of this study was to determine factors that influence tenderness independent of variation in pH, color, or marbling. To achieve the objective, 2 sample groups were chosen from a population of 159 pork loins aged 11 to 16 d. Predetermined ranges (ultimate pH, 5.54 to 5.86; marbling score, 1.0 to 3.0; percent total lipid, 1.61 to 3.37%) were defined for inclusion of individual loins in the study. The pork loins with the greatest ( = 12) and least ( = 12) Instron star probe values were assigned to 2 classification groups. The high star probe group had an average star probe that was 2.8 kg greater than the low star probe group (7.75 vs. 4.95 kg). Pork quality and sensory characteristics of pH, subjective and instrumental color values, cook loss, sensory tenderness, chewiness, juiciness, pork flavor, and off flavor were determined on fresh, never frozen pork chops. Lipid content, sarcomere length, myosin heavy-chain profile, and calpain autolysis were determined. Degradation of troponin-T, desmin, filamin, and titin were evaluated on the protein extracts from each sample. Pork loin pH, subjective color scores, Minolta L values, sarcomere length, and myosin heavy-chain composition were not different across groups. Chops from the low star probe group had a significantly greater marbling score (2.3 vs. 1.9) and lipid content (2.61 vs. 2.23%). Calpain-1 was completely autolyzed in both high and low star probe samples, demonstrating that calpain-1 potentially had been active in all samples. Low star probe whole-muscle protein extracts had more troponin-T ( < 0.01), desmin ( < 0.01), and filamin degradation ( < 0.01) than high star probe samples. Both classification groups showed degradation of titin. Remarkably, some high star probe samples still had observable intact bands of titin on SDS-PAGE gels. These results demonstrate that significant variation in instrumental tenderness is observed within a moderate pH range. Lipid content and proteolysis both appear to contribute to this variation.

Review: divergent selection for residual feed intake in the growing pig

This review summarizes the results from the INRA (Institut National de la Recherche Agronomique) divergent selection experiment on residual feed intake (RFI) in growing Large White pigs during nine generations of selection. It discusses the remaining challenges and perspectives for the improvement of feed efficiency in growing pigs. The impacts on growing pigs raised under standard conditions and in alternative situations such as heat stress, inflammatory challenges or lactation have been studied. After nine generations of selection, the divergent selection for RFI led to highly significant (P<0.001) line differences for RFI (-165 g/day in the low RFI (LRFI) line compared with high RFI line) and daily feed intake (-270 g/day). Low responses were observed on growth rate (-12.8 g/day, P<0.05) and body composition (+0.9 mm backfat thickness, P=0.57; -2.64% lean meat content, P<0.001) with a marked response on feed conversion ratio (-0.32 kg feed/kg gain, P<0.001). Reduced ultimate pH and increased lightness of the meat (P<0.001) were observed in LRFI pigs with minor impact on the sensory quality of the meat. These changes in meat quality were associated with changes of the muscular energy metabolism. Reduced maintenance energy requirements (-10% after five generations of selection) and activity (-21% of time standing after six generations of selection) of LRFI pigs greatly contributed to the gain in energy efficiency. However, the impact of selection for RFI on the protein metabolism of the pig remains unclear. Digestibility of energy and nutrients was not affected by selection, neither for pigs fed conventional diets nor for pigs fed high-fibre diets. A significant improvement of digestive efficiency could likely be achieved by selecting pigs on fibre diets. No convincing genetic or blood biomarker has been identified for explaining the differences in RFI, suggesting that pigs have various ways to achieve an efficient use of feed. No deleterious impact of the selection on the sow reproduction performance was observed. The resource allocation theory states that low RFI may reduce the ability to cope with stressors, via the reduction of a buffer compartment dedicated to responses to stress. None of the experiments focussed on the response of pigs to stress or challenges could confirm this theory. Understanding the relationships between RFI and responses to stress and energy demanding processes, as such immunity and lactation, remains a major challenge for a better understanding of the underlying biological mechanisms of the trait and to reconcile the experimental results with the resource allocation theory.

Proteomic features linked to tenderness of aged pork loins

There is considerable evidence that the protein component of fresh pork makes a major contribution to tenderness. In particular, the proteomic profile can be linked to postmortem events including pH decline, tissue oxidation, and protein degradation. The objectives for this study were to determine differences in sarcoplasmic proteomes that contribute to tenderness variation in aged pork longissimus dorsi muscles (LM). A defined set of pork loins selected to be similar in pH, color, and lipid yet different in tenderness were used. Pork loins were assigned to tenderness groups based on their star probe values; a high star probe group (HSP; n=12 mean star probe 7.75 kg) and low star probe group (LPS; n=12 star probe 4.95 kg) Samples were selected for proteomic experiments based on star probe values, and selected samples were within specified ranges for ultimate pH (5.54-5.86), marbling score (1.0-3.0), and percent total lipid (1.61-3.37%). Two-dimensional difference in gel electrophoresis (2D-DIGE) and mass spectrometry were used to examine sarcoplasmic protein abundance and potential modifications. Proteins spots that were significantly different across groups were selected for identification. Results from 2D-DIGE showed that HSP samples had significantly more abundant metabolic, stress response, and regulatory proteins in the sarcoplasmic fraction compared with LSP samples. The stress response protein peroxiredoxin-2 was more abundant in HSP samples as determined by 2D-DIGE ( ≤ 0.01; 2 spots) and western blot assay ( = 0.02). Low star probe samples showed significantly more degradation of the structural protein desmin in 2D-DIGE ( < 0.01) and western blot assay ( < 0.01). These results demonstrate that extreme proteolytic differences influenced measured tenderness of LSP and HSP samples and that soluble desmin and peroxiredoxin-2 may be used as biomarkers to differentiate between tough and tender aged pork products.

Post-weaning blood transcriptomic differences between Yorkshire pigs divergently selected for residual feed intake

Background

Improving feed efficiency (FE) of pigs by genetic selection is of economic and environmental significance. An increasingly accepted measure of feed efficiency is residual feed intake (RFI). Currently, the molecular mechanisms underlying RFI are largely unknown. Additionally, to incorporate RFI into animal breeding programs, feed intake must be recorded on individual pigs, which is costly and time-consuming. Thus, convenient and predictive biomarkers for RFI that can be measured at an early age are greatly desired. In this study, we aimed to explore whether differences exist in the global gene expression profiles of peripheral blood of 35 to 42 day-old pigs with extremely low (more efficient) and high RFI (less efficient) values from two lines that were divergently selected for RFI during the grow-finish phase, to use such information to explore the potential molecular basis of RFI differences, and to initiate development of predictive biomarkers for RFI.

Results

We identified 1972 differentially expressed genes (DEGs) (q ≤ 0.15) between the low (n = 15) and high (n = 16) RFI groups of animals by using RNA sequencing technology. We validated 24 of 37 selected DEGs by reverse transcription-quantitative PCR (RT-qPCR) in a joint analysis of 24 (12 per line) of the 31 samples already used for RNA-seq plus 24 (12 per line) novel samples from the same contemporary group of pigs. Using an analysis of the 24 novel samples alone, only nine of the 37 selected DEGs were validated. Genes involved in small molecule biosynthetic process, antigen processing and presentation of peptide antigen via major histocompatibility complex (MHC) class I, and steroid biosynthetic process were overrepresented among DEGs that had higher expression in the low versus high RFI animals. Genes known to function in the proteasome complex or mitochondrion were also significantly enriched among genes with higher expression in the low versus high RFI animals. Alternatively, genes involved in signal transduction, bone mineralization and regulation of phosphorylation were overrepresented among DEGs with lower expression in the low versus high RFI animals. The DEGs significantly overlapped with genes associated with disease, including hyperphagia, eating disorders and mitochondrial diseases (q < 1E-05). A weighted gene co-expression network analysis (WGCNA) identified four co-expression modules that were differentially expressed between the low and high RFI groups. Genes involved in lipid metabolism, regulation of bone mineralization, cellular immunity and response to stimulus were overrepresented within the two modules that were most significantly differentially expressed between the low and high RFI groups. We also found five of the DEGs and one of the co-expression modules were significantly associated with the RFI phenotype of individual animals (q < 0.05).

Conclusions

The post-weaning blood transcriptome was clearly different between the low and high RFI groups. The identified DEGs suggested potential differences in mitochondrial and proteasomal activities, small molecule biosynthetic process, and signal transduction between the two RFI groups and provided potential new insights into the molecular basis of RFI in pigs, although the observed relationship between the post-weaning blood gene expression and RFI phenotype measured during the grow-finish phase was not strong. DEGs and representative genes in co-expression modules that were associated with RFI phenotype provide a preliminary list for developing predictive biomarkers for RFI in pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2395-x) contains supplementary material, which is available to authorized users.

Whole Blood Transcriptomics Is Relevant to Identify Molecular Changes in Response to Genetic Selection for Feed Efficiency and Nutritional Status in the Pig

The molecular mechanisms underlying feed efficiency need to be better understood to improve animal efficiency, a research priority to support a competitive and sustainable livestock production. This study was undertaken to determine whether pig blood transcriptome was affected by differences in feed efficiency and by ingested nutrients. Growing pigs from two lines divergently selected for residual feed intake (RFI) and fed isoproteic and isocaloric diets contrasted in energy source and nutrients were considered. Between 74 and 132 days of age, pigs (n = 12 by diet and by line) received a regular diet rich in cereals and low in fat (LF) or a diet where cereals where partially substituted by lipids and fibers (HF). At the end of the feeding trial, the total number of white blood cells was not affected by the line or by the diet, whereas the red blood cell number was higher (P<0.001) in low RFI than in high RFI pigs. Analysis of the whole blood transcriptome using a porcine microarray reveals a higher number of probes differentially expressed (DE) between RFI lines than between diets (2,154 versus 92 probes DE, P<0.01). This corresponds to 528 overexpressed genes and 477 underexpressed genes in low RFI pigs compared with high RFI pigs, respectively. Overexpressed genes were predominantly associated with translational elongation. Underexpressed genes were mainly involved in the immune response, regulation of inflammatory response, anti-apoptosis process, and cell organization. These findings suggest that selection for RFI has affected the immune status and defense mechanisms of pigs. Genes DE between diets were mainly related to the immune system and lipid metabolism. Altogether, this study demonstrates the usefulness of the blood transcriptome to identify the main biological processes affected by genetic selection and feeding strategies.