Transcriptomic analysis of intestinal organoids, derived from pigs divergent in feed efficiency, and their response to Escherichia coli

BACKGROUND

There is increasing interest in using intestinal organoids to study complex traits like feed efficiency (FE) and host-microbe interactions. The aim of this study was to investigate differences in the molecular phenotype of organoids derived from pigs divergent for FE as well as their responses to challenge with adherent and invasive Escherichia coli (E. coli).

RESULTS

Colon and ileum tissue from low and high FE pigs was used to generate 3D organoids and two dimensional (2D) monolayers of organoid cells for E. coli challenge. Genome-wide gene expression was used to investigate molecular differences between pigs that were phenotypically divergent for FE and to study the difference in gene expression after challenge with E. coli. We showed, (1) minor differences in gene expression of colon organoids from pigs with low and high FE phenotypes, (2) that an E. coli challenge results in a strong innate immune gene response in both colon and ileum organoids, (3) that the immune response seems to be less pronounced in the colon organoids of high FE pigs and (4) a slightly stronger immune response was observed in ileum than in colon organoids.

CONCLUSIONS

These findings demonstrate the potential for using organoids to gain insights into complex biological mechanisms such as FE.

Review: Methods and biomarkers to investigate intestinal function and health in pigs

Society is becoming increasingly critical of animal husbandry due to its environmental impact and issues involving animal health and welfare including scientific experiments conducted on farm animals. This opens up two new fields of scientific research, the development of non- or minimally invasive (1) methods and techniques using faeces, urine, breath or saliva sampling to replace existing invasive models, and (2) biomarkers reflecting a disease or malfunction of an organ that may predict the future outcome of a pig's health, performance or sustainability. To date, there is a paucity of non- or minimally invasive methods and biomarkers investigating gastrointestinal function and health in pigs. This review describes recent literature pertaining to parameters that assess gastrointestinal functionality and health, tools currently used to investigate them, and the development or the potential to develop new non- and minimally invasive methods and/or biomarkers in pigs. Methods described within this review are those that characterise gastrointestinal mass such as the citrulline generation test, intestinal protein synthesis rate, first pass splanchnic nutrient uptake and techniques describing intestinal proliferation, barrier function and transit rate, and microbial composition and metabolism. An important consideration is gut health, and several molecules with the potential to act as biomarkers of compromised gut health in pigs are reported. Many of these methods to investigate gut functionality and health are considered 'gold standards' but are invasive. Thus, in pigs, there is a need to develop and validate non-invasive methods and biomarkers that meet the principles of the 3 R guidelines, which aim to reduce and refine animal experimentation and replace animals where possible.

Transcriptome Profiling of the Liver in Nellore Cattle Phenotypically Divergent for RFI in Two Genetic Groups

The identification and selection of genetically superior animals for residual feed intake (RFI) could enhance productivity and minimize environmental impacts. The aim of this study was to use RNA-seq data to identify the differentially expressed genes (DEGs), known non-coding RNAs (ncRNAs), specific biomarkers and enriched biological processes associated with RFI of the liver in Nellore cattle in two genetic groups. In genetic group 1 (G1), 24 extreme RFI animals (12 low RFI (LRFI) versus 12 high RFI (HRFI)) were selected from a population of 60 Nellore bulls. The RNA-seq of the samples from their liver tissues was performed using an Illumina HiSeq 2000. In genetic group 2 (G2), 20 samples of liver tissue of Nellore bulls divergent for RFI (LRFI, n = 10 versus HRFI, n = 10) were selected from 83 animals. The raw data of the G2 were chosen from the ENA repository. A total of 1811 DEGs were found for the G1 and 2054 for the G2 (p-value ≤ 0.05). We detected 88 common genes in both genetic groups, of which 33 were involved in the immune response and in blocking oxidative stress. In addition, seven (B2M, ADSS, SNX2, TUBA4A, ARHGAP18, MECR, and ABCF3) possible gene biomarkers were identified through a receiver operating characteristic analysis (ROC) considering an AUC > 0.70. The B2M gene was overexpressed in the LRFI group. This gene regulates the lipid metabolism protein turnover and inhibits cell death. We also found non-coding RNAs in both groups. MIR25 was up-regulated and SNORD16 was down-regulated in the LRFI for G1. For G2, up-regulated RNase_MRP and SCARNA10 were found. We highlight MIR25 as being able to act by blocking cytotoxicity and oxidative stress and RMRP as a blocker of mitochondrial damage. The biological pathways associated with RFI of the liver in Nellore cattle in the two genetic groups were for energy metabolism, protein turnover, redox homeostasis and the immune response. The common transcripts, biomarkers and metabolic pathways found in the two genetic groups make this unprecedented work even more relevant, since the results are valid for different herds raised in different ways. The results reinforce the biological importance of these known processes but also reveal new insights into the complexity of the liver tissue transcriptome of Nellore cattle.

Comparative effects of dietary methionine and cysteine supplementation on redox status and intestinal integrity in immunologically challenged-weaned pigs

Sulfur-containing amino acids such as methionine and cysteine play critical roles in immune system and redox status. A body of evidence shows that metabolic aspects of supplemented Met and Cys may differ in the body. Therefore, the study aimed to investigate the effects of dietary Met and Cys supplementation in immunologically challenged weaned pigs. Forty weaned piglets (6.5 ± 0.3 kg) were randomly allocated to five treatment groups. The treatment included: (1) sham-challenged control (SCC), (2) challenged control (CC), (3) MET (CC + 0.1% _DL-Met), (4) CYS (CC + 0.1% _L-Cys), and (5) MET + CYS (CC + 0.1% _DL-Met + 0.1% _L-Cys). On day 7, all pigs were intramuscularly injected with either Escherichia coli O55:B5 lipopolysaccharides (LPS) or phosphate-buffered saline. Blood, liver, and jejunum samples were analyzed for immune response and redox status. The CC group had lower (P < 0.05) villus surface area and higher (P < 0.05) flux of 4-kDa fluorescein isothiocyanate dextran (FD4) than the SCC group. A lower (P < 0.05) glutathione (GSH) concentration was observed in the jejunum of pigs in the CC group than those in the SCC group. Dietary Cys supplementation increased (P < 0.05) villus surface area, GSH levels, and reduced (P < 0.05) the flux of FD4 in the jejunum of LPS-challenged pigs. Dietary Met supplementation enhanced (P < 0.05) hepatic GSH content. Pigs challenged with LPS in the MET group had lower serum IL-8 concentration than those in the CC group. There was a Met × Cys interaction (P < 0.05) in serum IL-4 and IL-8 concentrations, and Trolox equivalent antioxidant capacity. Dietary _L-Cys supplementation restored intestinal integrity and GSH levels that were damaged by lipopolysaccharides administration. Dietary _DL-Met supplementation improved hepatic GSH and reduced systemic inflammatory response, but antagonistic interaction with dietary _L-Cys supplementation was observed in the inflammatory response and redox status.

Development of Intestinal Injury and Restoration of Weaned Piglets under Chronic Immune Stress

This study aimed to investigate the effects of lipopolysaccharide (LPS)-induced chronic immune stress on intestinal morphology and function, immune system, oxidative status, and mitochondrial function in piglets. Fifty healthy Duroc × Landrace × Yorkshire piglets (21 ± 2 days old, barrow, 6.98 ± 0.14 kg body weight) were selected and randomly allotted to five groups, which were slaughtered at 0 (0 group), 1, 5, 9, and 15 d of LPS injection. The results showed that compared with the piglets without LPS injection, LPS injection significantly impaired the intestinal morphology and permeability at 1, 5, and 9 d, as manifested by the increased serum lactic acid and decreased ratio of villus height to crypt depth (p < 0.05). Moreover, intestinal inflammation and oxidative and mitochondrial injury were caused at 1 d, as manifested by upregulated IL-6 mRNA expression, increased malondialdehyde content, and impaired mitochondrial morphology (p < 0.05). However, these parameters were restored to levels identical to 0 group at 9~15 d, accompanied by significantly increased antioxidant capacity, enhanced protein expression of CD3+ and CD68+, and upregulated mRNA abundance of genes related to mitochondrial biogenesis and functions (p < 0.05). Collectively, these results suggest that the intestinal injury of piglets caused by chronic immune stress could be self-repaired.

A quadruple protection procedure for resuming pig production in small-scale ASFV-positive farms in China

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African swine fever outbreak has caused serious economic losses in China. Pork supply in consequence faces huge demand.

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The small-scale farms in China are encountering difficulties in raising pigs.

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A comprehensive procedure was tested in 35 small pig farms that had been confirmed with African swine fever virus.

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During a one-year study, 100 percent of porkers and 98.8 percent of sows were healthy respectively.

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An effective biosafety procedure was developed for production of pigs in small-scale farms in China.

African swine fever (ASF) outbreak has caused serious economic losses in Asia since 2018. As ASF is a new emerging disease, many farmers hesitate to raise pigs before biosafety procedures were evaluated to be effective. To support small-scale farms in resuming pig production, a comprehensive procedure, called the quadruple protection procedure (QPP), was tested in 35 small farms which had been confirmed with African swine fever virus (ASFV). The QPP takes care of the farms' construction, environmental disinfection, regular immunization, and feed quality. Qualified daily management was supplemented as well. During a one-year survey four disinfectants and one piece of equipment were used in higher frequency. A 7- or 15-day empty period after the disinfection was suitable when it was combined with the rest of the protection measures from QPP. Totally 18,730 porkers and 3,006 sows were healthy by the end of the study with percentage of 100 and 98.8, respectively, indicating that QPP could protect pigs in small-scale farms from pathogens within China. This study developed an effective protective procedure system for small-scale farms to produce pigs under the risk of ASF outbreak.

Lawsonia intracellularis infected enterocytes lack sucrase-isomaltase which contributes to reduced pig digestive capacity

Lawsonia intracellularis is endemic to swine herds worldwide, however much is still unknown regarding its impact on intestinal function. Thus, this study aimed to characterize the impact of L. intracellularis on digestive function, and how vaccination mitigates these impacts. Thirty-six L. intracellularis negative barrows were assigned to treatment groups (n  =  12/trt): (1) nonvaccinated, L. intracellularis negative (NC); (2) nonvaccinated, L intracellularis challenged (PC); and (3) L. intracellularis challenged, vaccinated (Enterisol^® Ileitis, Boehringer Ingelheim) 7 weeks pre-challenge (VAC). On days post-inoculation (dpi) 0 PC and VAC pigs were inoculated with L. intracellularis. From dpi 19–21 fecal samples were collected for apparent total tract digestibility (ATTD) and at dpi 21, pigs were euthanized for sample collection. Post-inoculation, ADG was reduced in PC pigs compared with NC (41%, P  <  0.001) and VAC (25%, P  <  0.001) pigs. Ileal gross lesion severity was greater in PC pigs compared with NC (P  =  0.003) and VAC (P  =  0.018) pigs. Dry matter, organic matter, nitrogen, and energy ATTD were reduced in PC pigs compared with NC pigs (P  ≤  0.001 for all). RNAscope in situ hybridization revealed abolition of sucrase-isomaltase transcript in the ileum of PC pigs compared with NC and VAC pigs (P  <  0.01). Conversely, abundance of stem cell signaling markers Wnt3, Hes1, and p27^Kip1 were increased in PC pigs compared with NC pigs (P  ≤  0.085). Taken together, these data demonstrate that reduced digestibility during L. intracellularis challenge is partially driven by abolition of digestive machinery in lesioned tissue. Further, vaccination mitigated several of these effects, likely from lower bacterial burden and reduced disease severity.

Factors affecting performance response of pigs exposed to different challenge models: a multivariate approach

Factors associated with the severity with which different challenge models (CMs) compromise growth performance in pigs were investigated using hierarchical clustering on principal components (HCPC) analysis. One hundred seventy-eight studies reporting growth performance variables (average daily gain [ADG], average daily feed intake [ADFI], gain:feed [GF], and final body weight [FBW]) of a Control (Ct) vs. a Challenged (Ch) group of pigs using different CMs (enteric [ENT], environmental [ENV], lipopolysaccharide [LPS], respiratory [RES], or sanitary condition [SAN] challenges) were included. Studies were grouped by similarity in performance in three clusters (C1, C2, and C3) by HCPC. The effects of CM, cluster, and sex (males [M], females [F], mixed [Mi]) were investigated. Linear (LRP) and quadratic (QRP) response plateau models were fitted to assess the interrelationships between the change in ADG (∆ADG) and ADFI (∆ADFI) and the duration of challenge. All variables increased from C1 through C3, except for GF, which decreased (P < 0.05). LPS was more detrimental to ADG than ENV, RES, and SAN models (P < 0.05). Furthermore, LPS also lowered GF more than all the other CMs (P < 0.05). The ∆ADG independent of ∆ADFI was significant in LPS and SAN (P < 0.05), showed a trend toward the significance in ENT and RES (P < 0.10), and was not significant in ENV (P > 0.10), while the ∆ADG dependent on ∆ADFI was significant in ENT, ENV, and LPS only (P < 0.05). The critical value of ∆ADFI influencing the ∆ADG was significant in pigs belonging to C1 (P < 0.05) but not C2 or C3 (P > 0.10). The ∆ADG independent of duration post-Ch (irreparable portion of growth) was significant in C1 and C2 pigs, whereas the ∆ADFI independent of duration post-Ch (irreparable portion of feed intake) was significant in C1 pigs only (P < 0.05). Moreover, the time for recovery of ADG and ADFI after Ch was significant in pigs belonging to C1 and C2 (P < 0.05). Control F showed reduced ADG compared with Ct-M, and Ch-F showed reduced ADFI compared with Ch-M (P < 0.05). Moreover, the irreparable portion of ΔADG was 4.8 higher in F (-187.7; P < 0.05) compared with M (-39.1; P < 0.05). There are significant differences in growth performance response to CM based on cluster and sex. Furthermore, bacterial lipopolysaccharide appears to be an appropriate noninfectious model for immune stimulation and growth impairment in pigs.

Selection for feed efficiency elicits different postprandial plasma metabolite profiles in response to poor hygiene of housing conditions in growing pigs

This study was conducted to compare postprandial plasma concentrations of insulin, energy-related metabolites, and amino acids measured after a 6-week challenge consisting of exposure to good or poor hygiene of housing conditions of 24 growing pigs divergently selected for low-RFI (LRFI) and high-RFI (HRFI). Blood indicators of immune responses were assessed from samples collected before 0 (W0), and 3 (W3), and 6 weeks (W6) after pigs transfer to their respective hygiene of housing conditions. Plasma haptoglobin concentrations and blood neutrophil granulocyte numbers were greater in poor than in good hygiene of housing conditions at W3. Plasma concentrations of total immunoglobulin G were greater (p = 0.04) in poor than in good hygiene of housing conditions at W6. At W6, pigs were fitted with an intravenous catheter for serial blood samplings. Low-RFI pigs had greater insulin (p < 0.001) and lower triglyceride (p = 0.04) average plasma concentrations than HRFI pigs in both conditions. In poor hygiene of housing conditions, the peaks of insulin and glucose were observed earlier and that of insulin was greater in LRFI than in HRFI pigs. Irrespective of genetic line, average plasma concentrations of histidine, isoleucine, leucine, methionine, threonine, valine, and alanine were greater in poor compared with good hygiene of housing conditions. Only HRFI pigs had greater lysine, asparagine, proline, and tyrosine plasma concentrations in poor than in good hygiene of housing conditions. Conversely, arginine, tryptophan, proline, and tyrosine plasma concentrations were lower only for LRFI pigs housed in poor hygiene conditions. Our results suggest that, contrary to HRFI, LRFI pigs increase or maintain their utilization of tryptophan, arginine, and lysine when housed in poor hygiene conditions. This indicates that this difference may contribute to the better capacity of LRFI to cope with poor hygiene of housing conditions.

Brain Transcriptome Analysis Reveals Potential Transcription Factors and Biological Pathways Associated with Feed Efficiency in Commercial DLY Pigs

Feed efficiency (FE) is one of the most important economic traits in the porcine industry. In this study, high-throughput RNA sequencing (RNA-seq) was first utilized for brain tissue transcriptome analysis in pigs to indicate the potential genes and biological pathways related to FE in pigs. A total of 8 pigs with either extremely high-FE group (HE-group) or low-FE group (LE-group) were selected from 225 Duroc × (Landrace × Yorkshire) (DLY) pigs for transcriptomic analysis. RNA-seq analysis was performed to determine differentially expressed genes (DEGs) between the HE- and LE-group, and 430 DEGs were identified in brain tissues of pigs (|log₂(FoldChange)| > 1; adjusted p-values <0.05). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEGs were mainly enriched in synaptic signaling or transmission, and hormone secretion pathways, in which insulin secretion, and oxytocin signaling pathways were closely associated with FE by regulating feeding behavior and energy metabolism (adjusted p-values <0.05). Further, the transcription factors (TFs) analysis and gene co-expression network analysis indicated three hub differentially expressed TFs (NR2F2, TFAP2D, and HNF1B) that affected FE by mainly regulating feeding behavior, insulin sensitivity, or energy metabolism. Our findings suggest several potential TFs and biological pathways for further investigations of FE in pigs.

Effects of divergent selection for residual feed intake on nitrogen metabolism and lysine utilization in growing pigs

A study was conducted to evaluate the effects of divergent genetic selection for residual feed intake (RFI) on nitrogen (N) metabolism and lysine utilization in growing pigs. Twenty-four gilts (body weight [BW] 66 ± 5 kg) were selected from generation nine of the low RFI (LRFI; n = 12) and high RFI (HRFI; n = 12) Iowa State University Yorkshire RFI selection lines. Six pigs from each genetic line were assigned to each of two levels of lysine intake: 70% and 100% of estimated requirements based on the potential of each genetic line for protein deposition (PD) and feed intake. For all diets, lysine was first limiting among amino acids. Using isotope tracer, N-balance, and nutrient digestibility evaluation approaches, whole-body N metabolism and the efficiency of lysine utilization were determined for each treatment group. No significant interaction effects of line and diet on dietary N or gross energy digestibility, PD, and the efficiency of lysine utilization for PD were observed. The line did not have a significant effect on PD and digestibility of dietary N and GE. An increase in lysine intake improved N retention in both lines (from 15.0 to 19.6 g/d, SE 1.44, in LRFI pigs; and from 16.9 to 19.8 g/d, SE 1.67, in HRFI pigs; P < 0.01). At the low lysine intakes and when lysine clearly limited PD, the efficiency of using available lysine intake (above maintenance requirements) for PD was 80% and 91% (SE 4.6) for the LRFI and HRFI pigs, respectively (P = 0.006). There were no significant effects of line or of the line by diet interaction on N flux, protein synthesis, and protein degradation. Lysine intake significantly increased (P < 0.05) N flux (from 119 to 150, SE 8.7 g/d), protein synthesis (from 99 to 117, SE 10.6 g of N/d), and protein degradation (from 85 to 100, SE 6.6 g of N/d). The protein synthesis-to-retention ratio tended to be higher in the LRFI line compared with the HRFI line (6.5 vs. 5.8 SE 0.62; P = 0.06), indicating a tendency for the lower efficiency of PD in this group. Collectively, these results indicate that genetic selection for low RFI is not associated with improvements in lysine utilization efficiency, protein turnover, and nutrient digestibility.

Colonic microbiome profiles for improved feed efficiency can be identified despite major effects of farm of origin and contemporary group in pigs

While feed efficiency (FE) is a trait of great economic importance to the pig industry, the influence of the intestinal microbiome in determining FE is not well understood. The objective of this experiment was to determine the relative influence of FE and farm of birth on the pig colonic microbiome. Animals divergent in residual feed intake (RFI) were sourced from two geographically distinct locations (farms A + B) in Ireland. The 8 most efficient (low RFI (LRFI)) and 8 least efficient (high RFI, (HRFI)) pigs from farm A and 12 LRFI and 12 HRFI pigs from farm B were sacrificed. Colonic digesta was collected for microbial analysis using 16S ribosomal RNA gene sequencing and also for volatile fatty acid analysis. The α-diversity differed between the farms in this study, with pigs from farm A having greater diversity based on Shannon and InvSimpson measures compared to pigs from farm B (P < 0.05), with no difference identified in either Chao1 or observed measures of diversity (P > 0.05). In the analysis of β-diversity, pigs clustered based on farm of birth rather than RFI. Variation in the management of piglets, weight of the piglets, season of the year, sanitary status and dam dietary influence could potentially be causative factors in this large variation between farms. However, despite significant variation in the microbial profile between farms, consistent taxonomic differences were identified between RFI groups. Within the phylum Bacteroidetes, the LRFI pigs had increased abundance of BS11 (P < 0.05) and a tendency toward increased Bacteroidaceae (P < 0.10) relative to the HRFI group. At genus level, the LRFI pigs had increased abundance of Colinsella (P < 0.05), a tendency toward increased Bacteroides and CF231 (P < 0.10). At species level, Ruminococcus flavefaciens had increased abundance in the LRFI compared to the HRFI animals. In conclusion, while farm of birth has a substantial influence on microbial diversity in the pig colon, a microbial signature indicative of FE status was apparent.

Impact of viral disease hypophagia on pig jejunal function and integrity

Pathogen challenges are often accompanied by reductions in feed intake, making it difficult to differentiate impacts of reduced feed intake from impacts of pathogen on various response parameters. Therefore, the objective of this study was to determine the impact of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) and feed intake on parameters of jejunal function and integrity in growing pigs. Twenty-four pigs (11.34 ± 1.54 kg BW) were randomly selected and allotted to 1 of 3 treatments (n = 8 pigs/treatment): 1) PRRSV naïve, ad libitum fed (Ad), 2) PRRSV-inoculated, ad libitum fed (PRRS+), and 3) PRRSV naïve, pair-fed to the PRRS+ pigs' daily feed intake (PF). At 17 days post inoculation, all pigs were euthanized and the jejunum was collected for analysis. At days post inoculation 17, PRRS+ and PF pigs had decreased (P < 0.05) transepithelial resistance compared with Ad pigs; whereas fluorescein isothiocyanate-dextran 4 kDa permeability was not different among treatments. Active glucose transport was increased (P < 0.05) in PRRS+ and PF pigs compared with Ad pigs. Brush border carbohydrase activity was reduced in PRRS+ pigs compared with PF pigs for lactase (55%; P = 0.015), sucrase (37%; P = 0.002), and maltase (30%; P = 0.015). For all three carbohydrases, Ad pigs had activities intermediate that of PRRS+ and PF pigs. The mRNA abundance of the tight junction proteins claudin 2, claudin 3, claudin 4, occludin, and zonula occludens-1 were reduced in PRRS+ pigs compared with Ad pigs; however, neither the total protein abundance nor the cellular compartmentalization of these tight junction proteins differed among treatments. Taken together, this study demonstrates that the changes that occur to intestinal epithelium structure, function, and integrity during a systemic PRRSV challenge can be partially explained by reductions in feed intake. Further, long term adaptation to PRRSV challenge and caloric restriction does reduce intestinal transepithelial resistance but does not appear to reduce the integrity of tight junction protein complexes.

Acute systemic inflammatory response to lipopolysaccharide stimulation in pigs divergently selected for residual feed intake

Background

It is unclear whether improving feed efficiency by selection for low residual feed intake (RFI) compromises pigs’ immunocompetence. Here, we aimed at investigating whether pig lines divergently selected for RFI had different inflammatory responses to lipopolysaccharide (LPS) exposure, regarding to clinical presentations and transcriptomic changes in peripheral blood cells.

Results

LPS injection induced acute systemic inflammation in both the low-RFI and high-RFI line (n = 8 per line). At 4 h post injection (hpi), the low-RFI line had a significantly lower (p = 0.0075) mean rectal temperature compared to the high-RFI line. However, no significant differences in complete blood count or levels of several plasma cytokines were detected between the two lines. Profiling blood transcriptomes at 0, 2, 6, and 24 hpi by RNA-sequencing revealed that LPS induced dramatic transcriptional changes, with 6296 genes differentially expressed at at least one time point post injection relative to baseline in at least one line (n = 4 per line) (|log₂(fold change)| ≥ log₂(1.2); q < 0.05). Furthermore, applying the same cutoffs, we detected 334 genes differentially expressed between the two lines at at least one time point, including 33 genes differentially expressed between the two lines at baseline. But no significant line-by-time interaction effects were detected. Genes involved in protein translation, defense response, immune response, and signaling were enriched in different co-expression clusters of genes responsive to LPS stimulation. The two lines were largely similar in their peripheral blood transcriptomic responses to LPS stimulation at the pathway level, although the low-RFI line had a slightly lower level of inflammatory response than the high-RFI line from 2 to 6 hpi and a slightly higher level of inflammatory response than the high-RFI line at 24 hpi.

Conclusions

The pig lines divergently selected for RFI had a largely similar response to LPS stimulation. However, the low-RFI line had a relatively lower-level, but longer-lasting, inflammatory response compared to the high-RFI line. Our results suggest selection for feed efficient pigs does not significantly compromise a pig’s acute systemic inflammatory response to LPS, although slight differences in intensity and duration may occur.

Immune system stimulation induced by porcine reproductive and respiratory syndrome virus alters plasma free amino acid flux and dietary nitrogen utilization in starter pigs1

Changes in plasma free amino acid (AA) flux reflect the modification of AA metabolism in different metabolic states. Infectious diseases repartition AA away from protein retention toward processes involved in immune defense, thus impacting AA utilization in pigs. The current study sought to evaluate the effects of disease induced by a live pathogen on plasma free AA flux and whole-body nitrogen (N) utilization. Twenty gilts (BW 9.4 ± 0.9 kg) were surgically catheterized into the jugular vein, individually housed in metabolism crates, and feed-restricted (550 g/d). Intramuscular inoculation of a live field strain of porcine reproductive and respiratory syndrome virus (PRRSV) was used to induce disease. Whole-body N-balance was conducted across 3 d both before PRRSV inoculation (PRRSV-) and also after PRRSV inoculation (PRRSV+). At the end of each N-balance period, a bolus dose of a labeled [U-13C, U-15N]-AA mixture (Ile, Leu, Lys, Met, Phe, Thr, Trp, Val, and Gln) was infused intravenously, followed by serial blood collection for measurement of isotopic enrichment. A double exponential model was fitted with plasma enrichment data for each pig and each AA, and equation parameters were used to estimate plasma free AA flux and pool size. Apparent ileal digestibility (AID) of dietary N was determined using the slaughter technique and an indigestible marker. Blood chemistry, hematology, body temperature, and serum viremia indicated that PRRSV induced effective immune response in pigs (P < 0.05). Challenge with PRRSV reduced the AID of N (P < 0.05), but had no effect on apparent total tract digestibility of dietary energy (P = 0.12). Plasma flux (µmol/kg BW/h) for Met and Thr was increased by PRRSV infection (P < 0.05). A strong tendency of increased Val flux was observed in PRRSV+ pigs (P = 0.06). Infection with PRRSV increased the pool size for Lys, Met, Thr, Trp, Leu, Val, and Gln (P < 0.05). Collectively, these results suggest that PRRSV alters the utilization of dietary N and AA flux, as well as pool size, in growing pigs. The increase in Thr and Met flux in PRRSV+ pigs may be associated with enhanced utilization of these AA for the synthesis of immune system metabolites and increased catabolism of these AA. Thus, dietary Met, Thr, and Val requirements may increase in pigs infected with PRRSV, relative to the requirements for other AA.

Analysis of the basal colonic innate immune response of pigs divergent in feed efficiency and following an ex vivo lipopolysaccharide challenge

While feed efficiency is influenced by multiple physiological processes, it is not known how efficient and inefficient pigs differ in relation to their basal immune response, and particularly their innate immune response to a microbial challenge. Hence, the objective was to examine the expression of genes encoding innate immune response markers in basal colonic tissue and colonic tissue following an ex vivo lipopolysaccharide (LPS) challenge from pigs divergent in residual feed intake (RFI). Pigs that differed in RFI were selected from two different farms of origin. Colonic tissue was harvested from high RFI (HRFI) and low (LRFI) pigs, and two experimental conditions were explored: the first was basal unchallenged tissue and the second was colonic tissue following an ex vivo LPS challenge. RNA was extracted and tested on a Nanostring panel of 72 genes coding for barrier defense proteins, transmembrane receptors, kinases, transcription regulators, cytokines, and cytokine regulators. In the basal unchallenged tissue, the LRFI pigs had increased expression of AOAH, AP1, and TRAM and the cytokines TNF, IL10, and CXCL8, compared with the HRFI pigs (P < 0.05), with a significant effect of farm of origin on 31 genes (P < 0.05). In the LPS-challenged tissues, the LRFI group had higher expression of TLR1, TLR7, TLR8, GPR43/FFAR2, JAK2, and NFAM1 compared with the HRFI group (P < 0.05). In conclusion, these data suggest that LRFI pigs have an upregulated basal colonic inflammatory state and a heightened response to an LPS challenge compared with the inefficient HRFI pigs. This immune profile potentially enhances their capacity to respond to an infectious challenge.

Immune System Stimulation Reduces the Efficiency of Whole-Body Protein Deposition and Alters Muscle Fiber Characteristics in Growing Pigs

Simple Summary

Disease reduces growth and protein retention in pigs. Protein retention is the balance between two energy-consuming processes in the body of pigs: protein synthesis and breakdown. Previous reports on the effects of disease on these components of protein metabolism and their consecutive effects on protein retention are inconsistent. In addition, limited information is available about the effects of disease on the composition of muscle fibers in pigs. Thus, we evaluated these parameters, since they help us to understand protein metabolism during disease in pigs. We used twelve gilts; five were used as a control and seven were made ill. Experimental diets were designed to supply nutrients that closely met the daily requirements of each group. Protein synthesis, protein breakdown, and protein retention were measured over 72 h. Pigs were then euthanized and various muscles were sampled. Our findings suggested that disease not only reduces protein retention by decreasing protein synthesis and protein breakdown, but also by reducing the efficiency of protein deposition. In other words, ill pigs synthesize more protein per unit of protein retention, compared to healthy pigs. In addition, disease reduces muscle mass and changes the composition of the muscle fibers. The latter might negatively affect pork quality.

Abstract

The effects of immune system stimulation (ISS), induced by repeated injection of Escherichia coli lipopolysaccharide, on the whole-body protein synthesis versus degradation rates, the efficiency of protein deposition (PD), and muscle fiber characteristics in pigs were evaluated. Twelve growing gilts were assigned to two levels of amino acid intake that was predicted based on the potential of each group’s health status for PD and feed intake. Isotope tracer, nitrogen balance, and immunohistochemical staining techniques were used to determine protein turnover, PD, and muscle fiber characteristics, respectively. Protein synthesis, degradation, and PD were lower in immune-challenged pigs than in control pigs (p < 0.05). Strong tendencies for a higher protein synthesis-to-PD ratio (p = 0.055) and a lower protein synthesis-to-degradation ratio (p = 0.065) were observed in immune-challenged pigs. A decrease in muscle cross-sectional area of fibers and a shift from myosin heavy chain (MHC)-II towards MHC-I fibers (p < 0.05) were observed in immune-challenged pigs. These results indicated that ISS reduces PD not only by suppressing the whole-body protein synthesis and degradation rates, but also by decreasing the efficiency of PD in growing pigs. In addition, ISS induces atrophy in skeletal muscles and favors a slow-twitch oxidative fiber type composition.

A comparative analysis of the transcriptome profiles of liver and muscle tissue in pigs divergent for feed efficiency

BACKGROUND

The improvement of feed efficiency is a key economic goal within the pig production industry. The objective of this study was to examine transcriptomic differences in both the liver and muscle of pigs divergent for feed efficiency, thus improving our understanding of the molecular mechanisms influencing feed efficiency and enabling the identification of candidate biomarkers. Residual feed intake (RFI) was calculated for two populations of pigs from two different farms of origin/genotype. The 6 most efficient (LRFI) and 6 least efficient (HRFI) animals from each population were selected for further analysis of Longissimus Dorsi muscle (n = 22) and liver (n = 23). Transcriptomic data were generated from liver and muscle collected post-slaughter.

RESULTS

The transcriptomic data segregated based on the RFI value of the pig rather than genotype/farm of origin. A total of 6463 genes were identified as being differentially expressed (DE) in muscle, while 964 genes were identified as being DE in liver. Genes that were commonly DE between muscle and liver (n = 526) were used for the multi-tissue analysis. These 526 genes were associated with protein targeting to membrane, extracellular matrix organisation and immune function. In the muscle-only analysis, genes associated with RNA processing, protein synthesis and energy metabolism were down regulated in the LRFI animals while in the liver-only analysis, genes associated with cell signalling and lipid homeostasis were up regulated in the LRFI animals.

CONCLUSIONS

Differences in the transcriptome segregated on pig RFI value rather than the genotype/farm of origin. Multi-tissue analysis identified that genes associated with GO terms protein targeting to membrane, extracellular matrix organisation and a range of terms relating to immune function were over represented in the differentially expressed genes of both liver and muscle.

Immune system stimulation increases dietary threonine requirements for protein deposition in growing pigs

Previous studies have reported an increase in the utilization of threonine (Thr) during immune system stimulation (ISS). However, increased utilization of an AA during ISS may not reflect an increased dietary requirement, as endogenous sources may supply AA to meet the need for enhanced utilization. The current study evaluated the impact of ISS on components of dietary Thr requirements, i.e., maintenance requirement and the efficiency of Thr utilization. Thirty-nine gilts (initial BW 32 ± 2.1 kg) of commercially relevant genetics were individually housed in metabolism crates and fed one of six experimental diets in which Thr was the first limiting among other AA. Three levels of dietary Thr were tested within each ISS group: 70%, 90%, and 110% of daily Thr requirements, which were estimated based on the potential of each ISS group for protein deposition (PD). Following adaptation to the experimental diets, pigs from each dietary treatment group were injected with either increasing amounts of Escherichia coli lipopolysaccharide (ISS+; 25 and 35 µg/kg BW) or saline (ISS-). Injections were given 48-h apart and whole-body nitrogen balance was measured for 72-h following the first injection. Body temperature (BT) was monitored and blood samples were collected 24 h after initiation of ISS and evaluated for measures of blood chemistry. Blood chemistry and BT results indicated an effective ISS in pigs (P < 0.03). Threonine intake increased PD in a linear fashion in both ISS groups (P < 0.01). The marginal efficiency of standardized ileal digestible (SID) Thr utilization for PD, represented by the slope, was not affected by ISS. However, ISS substantially increased the extrapolated maintenance SID Thr requirements, represented by the intercept at zero PD (ISS- vs. ISS+, -11.2 vs. -56.3 SE 13.2; P < 0.05). Collectively, our results indicated that the physiological changes associated with ISS increased the dietary SID Thr requirements for PD due to an increase in maintenance requirements.

Immune system stimulation induced by Escherichia coli lipopolysaccharide alters plasma free amino acid flux and dietary nitrogen utilization in growing pigs

Changes in plasma free AA flux reflect the modification of AA metabolism in different metabolic states. Immune system stimulation (ISS) in growing pigs may redistribute AA from protein retention towards processes involved in the immune response, thus impacting AA utilization. The aim of the current study was to evaluate the effect of ISS on whole-body nitrogen (N) utilization and the kinetics of plasma free AA. Ten gilts (BW 9.4 ± 1.1 kg) were surgically fitted with jugular vein catheters, individually housed in metabolism crates, and feed-restricted (550 g/d). Repeated intramuscular injections of increasing amounts of Escherichia coli lipopolysaccharide (LPS) were used to induce ISS (30 and 36 µg/kg BW, given 48 h apart). Whole-body N-balance was determined for 3-d before ISS (ISS-) and 3-d during ISS (ISS+). At the end of each N-balance period, a bolus dose of labeled [U-13C, U-15N]-AA mixture (Ile, Leu, Lys, Met, Phe, Thr, Trp, Val, and Gln) was infused intravenously, followed by serial blood collection for determination of isotopic enrichment. A double exponential model was fitted with plasma enrichment data for each pig and each AA, and equation parameters were used to estimate plasma-free AA flux and pool size. Apparent ileal digestibility (AID) of N was determined using the slaughter technique and an indigestible marker. Blood samples were collected before and 76-h after the initiation of ISS and assayed for hematology and blood chemistry. Body temperature (BT) was monitored during the course of study. Blood chemistry, hematology, and BT results indicated that LPS induced effective ISS in pigs (P < 0.05). ISS tended to reduce N retention (P = 0.09) and the N retention-to-N intake ratio (P = 0.08). Apparent total tract digestibility of dietary energy and AID of N were reduced by ISS (P < 0.05). Plasma flux (µmol/kg BW/h) for Ile and Phe was reduced by ISS (P < 0.05). Strong tendencies for decreased Lys flux and N retention were observed in ISS pigs (P < 0.10). ISS increased the pool size for Leu but reduced the pool size for Ile (P < 0.05). Collectively, these results suggest that ISS alters the utilization of dietary N and AA flux, as well as pool size in growing pigs. The decrease in Lys, Phe, and Ile flux during ISS may be attributed to a reduction in whole-body protein synthesis or decreased catabolism of these AA. Relative to other AA, dietary Lys, Phe, and Ile requirements may decrease in ISS pigs.

Metabolic adaptation of pigs to a Mycoplasma hyopneumoniae and Lawsonia intracellularis dual challenge

Respiratory and enteric pathogens such as Mycoplasma hyopneumoniae (Mh) and Lawsonia intracellularis (LI) reduce lean accretion and feed efficiency (FE) in growing pigs. However, the metabolic mechanism by which this occurs is still unknown. Therefore, the primary aim of this study was to examine the metabolic adaptation of pigs presented with a dual Mh and LI challenge (MhLI). A secondary objective was to examine if selection for high FE, modeled by selection for low residual feed intake (RFI), alters molecular response to disease. Using a 2 × 2 factorial design, 6 littermate pairs from a high RFI (HRFI) and 6 littermate pairs from a low RFI (LRFI) line (barrows, 66 ± 2 kg BW) were selected, with 1 pig from each pair assigned to individual pens in either the challenge or the nonchallenge (control) rooms (n = 6 barrows per line/challenge). On days post inoculation (dpi) 0, MhLI pigs were inoculated intragastrically with LI and intratracheally with Mh. Pig and feeder weights were recorded at dpi 0, 7, 14, and 21. On dpi 21, pigs were euthanized and tissues and blood were collected. Markers of oxidative stress, skeletal muscle metabolism and proteolysis, and liver gluconeogenesis were evaluated to determine the effects of MhLI, RFI line, and their interaction. The interaction of line and challenge was not significant (P > 0.05) for any measure. Overall, MhLI pigs had lower ADG (38%, P < 0.001), ADFI (25%, P < 0.001), and G:F (19%, P = 0.012) compared with controls. As expected, LRFI pigs had lower ADFI (P = 0.028) for the same ADG, giving them greater G:F (P = 0.021) than HRFI pigs. Challenged pigs had greater reactive oxygen species (ROS) production in the LM and liver (P < 0.10) but did not have greater skeletal muscle proteolysis. Liver gluconeogenesis was also not upregulated (P > 0.05) due to MhLI. These results provide further evidence that selection for LRFI does not negatively affect response to disease. In addition, these results suggest that postabsorptive metabolic functions are altered due to MhLI challenge. The MhLI challenge induced mitochondrial dysfunction, evident by greater ROS production, and caused pigs to favor glycolytic energy generation. However, skeletal muscle proteolysis and liver gluconeogenesis were not upregulated during MhLI challenge. These data suggest that during mild disease stress, pigs can meet energy demands without reliance on nutrient mobilization and gluconeogenesis.

Lipopolysaccharide immune stimulation but not β-mannanase supplementation affects maintenance energy requirements in young weaned pigs

Background

Pathogen or diet-induced immune activation can partition energy and nutrients away from growth, but clear relationships between immune responses and the direction and magnitude of energy partitioning responses have yet to be elucidated. The objectives were to determine how β-mannanase supplementation and lipopolysaccharide (LPS) immune stimulation affect maintenance energy requirements (MEm) and to characterize immune parameters, digestibility, growth performance, and energy balance.

Methods

In a randomized complete block design, 30 young weaned pigs were assigned to either the control treatment (CON; basal corn, soybean meal and soybean hulls diet), the enzyme treatment (ENZ; basal diet + 0.056% β-mannanase), or the immune system stimulation treatment (ISS; basal diet + 0.056% β-mannanase, challenged with repeated increasing doses of Escherichia coli LPS). The experiment consisted of a 10-d adaptation period, 5-d digestibility and nitrogen balance measurement, 22 h of heat production (HP) measurements, and 12 h of fasting HP measurements in indirect calorimetry chambers. The immune challenge consisted of 4 injections of either LPS (ISS) or sterile saline (CON and ENZ), one every 48 h beginning on d 10. Blood was collected pre- and post-challenge for complete blood counts with differential, haptoglobin and mannan binding lectin, 12 cytokines, and glucose and insulin concentrations.

Results

Beta-mannanase supplementation did not affect immune status, nutrient digestibility, growth performance, energy balance, or ME_m. The ISS treatment induced fever, elevated proinflammatory cytokines and decreased leukocyte concentrations (P < 0.05). The ISS treatment did not impact nitrogen balance or nutrient digestibility (P > 0.10), but increased total HP (21%) and ME_m (23%), resulting in decreased lipid deposition (−30%) and average daily gain (−18%) (P < 0.05).

Conclusions

This experiment provides novel data on β-mannanase supplementation effects on immune parameters and energy balance in pigs and is the first to directly relate decreased ADG to increased ME_m independent of changes in feed intake in immune challenged pigs. Immune stimulation increased energy partitioning to the immune system by 23% which limited lipid deposition and weight gain. Understanding energy and nutrient partitioning in immune-stressed pigs may provide insight into more effective feeding and management strategies.

Electronic supplementary material

The online version of this article (10.1186/s40104-018-0264-y) contains supplementary material, which is available to authorized users.

Impact of Mycoplasma hyopneumoniae and Lawsonia intracellularis on the performance of pigs divergently selected for feed efficiency

Feed efficiency (FE) is a valuable trait, yet how genetic selection for enhanced FE affects other processes such as response to disease is unknown. Disease from endemic respiratory and enteric pathogens such as Mycoplasma hyopneumoniae (Mh) and Lawsonia intracellularis (LI) are common in swine production. Therefore, the aim of this study was to examine if pigs selected for high vs. low FE based on residual feed intake (RFI) respond differently to a dual respiratory and enteric challenge. Pigs selected for low RFI (LRFI, high FE) are considered more FE compared to their high RFI (HRFI, low FE) selected counterparts. Using a 2 × 2 factorial design, 25 littermate pairs from the HRFI and 25 littermate pairs from the LRFI line (barrows, 50 ± 7 kg BW) were selected, with one pig from each pair assigned to individual pens in either the challenge or the nonchallenge (control) rooms (n = 25 barrows/line/challenge). On days post inoculation (dpi) 0, the challenged pigs were inoculated with LI and Mh (MhLI). Feed intake, BW, fecal swabs, and serum samples were collected and recorded weekly for 42 d. On dpi -2 and 47, 14 littermate pairs (n = 7 barrows/line/challenge) were utilized for initial and final body composition scans using dual-energy X-ray absorptiometry to calculate longitudinal whole body tissue accretion rates for lean, protein, fat, and bone mineral content. Serum antibody levels and fecal shedding of LI were used to confirm infection. Control pigs remained negative by all measures during the 6-wk trial and MhLI inoculated pigs were confirmed positive via serological antibody responses by dpi 14 for LI and Mh. There were no interactions between RFI line and challenge status for any overall performance parameter (P > 0.05). The 6-wk MhLI challenge resulted in a 17% reduction in ADG, a 12% reduction in ADFI, and a 7% reduction in G:F vs. Controls (P < 0.05). In addition, compared to the Control pigs, MhLI challenge reduced lean, protein, and lipid accretion rates by 16% (P < 0.05). Genetic selection for high FE resulted in decreased ADFI and increased G:F (P < 0.01), but did not impact ADG or tissue accretion vs. low FE pigs. Collectively, these results demonstrate that a dual enteric and respiratory pathogen challenge reduced ADG, ADFI, G:F, and tissue accretion in growing pigs. Further, there was no evidence that selection for enhanced FE based on RFI index affects response to disease.

Diurnal heat stress reduces pig intestinal integrity and increases endotoxin translocation

Heat stress negatively affects performance and intestinal integrity of pigs. The objective of this study was to characterize the effects of diurnal heat stress (dHS) on nursery-grower pig performance, intestinal integrity, and lipopolysaccharide (LPS) translocation. Forty-eight nursery-grower gilts, individually penned, were randomly assigned to two treatments. Twenty-four pigs were then exposed to dHS for 3 d, 6 h at 38°C and 18 h at 32°C, at 40-60% humidity. The remaining pigs were maintained under thermal neutral (TN) conditions. Changes in pig rectal temperatures (Tr), respiration rates (RR), performance, and blood parameters were evaluated. Additionally, ex vivo ileum integrity was assessed with the Ussing chamber by measuring transepithelial resistance (TER), and 4 kDa fluorescein isothiocyanate (FITC)-dextran (FD4) and FITC-LPS mucosal to serosal flux. As expected, dHS increased pig Tr and RR (P < 0.05) and reduced pig performance (P < 0.05) on the 3-d period. Compared with TN, ileum TER (P = 0.04), FITC-LPS (P < 0.001), and FD4 (P = 0.011) permeability were significantly increased due to dHS. Compared with TN pigs, dHS increased serum endotoxin by 150% (P = 0.031). Altogether, 3-d dHS significantly reduced pig performance and intestinal integrity and increased blood endotoxin concentrations.

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.

Genome-wide association analysis and functional annotation of positional candidate genes for feed conversion efficiency and growth rate in pigs

Feed conversion efficiency is a measure of how well an animal converts feed into live weight and it is typically expressed as feed conversion ratio (FCR). FCR and related traits like growth rate (e.g. days to 110 kg—D110) are of high interest for animal breeders, farmers and society due to implications on animal performance, feeding costs and environmental sustainability. The objective of this study was to identify genomic regions associated with FCR and D110 in pigs. A total of 952 terminal line boars, showing an individual variation in FCR, were genotyped using 60K SNP-Chips. Markers were tested for associations with estimated breeding values (EBV) for FCR and D110. For FCR, the largest number of associated SNPs was located on chromosomes 4 (30 SNPs), 1 (25 SNPs), X (15 SNPs) and 6 (12 SNPs). The most prominent genomic regions for D110 were identified on chromosomes 15 (10 SNPs), 1 and 4 (both 9 SNPs). The most significantly associated SNPs for FCR and D110 mapped 129.8 Kb from METTL11B (chromosome 4) and 32Kb from MBD5 (chromosome 15), respectively. A list of positional genes, closest to significantly associated SNPs, was used to identify enriched pathways and biological functions related to the QTL for both traits. A number of candidate genes were significantly overrepresented in pathways of immune cell trafficking, lymphoid tissue structure, organ morphology, endocrine system function, lipid metabolism, and energy production. After resequencing the coding region of selected positional and functional candidate genes, six SNPs were genotyped in a subset of boars. SNPs in PRKDC, SELL, NR2E1 and AKRIC3 showed significant associations with EBVs for FCR/D110. The study revealed a number of chromosomal regions and candidate genes affecting FCR/D110 and pointed to corresponding biological pathways related to lipid metabolism, olfactory reception, and also immunological status.

Effect of supplemental dietary leucine and immune system stimulation on whole-body nitrogen utilization in starter pigs

The increase in circulating pro-inflammatory cytokines following an immune challenge (e.g., with bacterial lipopolysaccharide [LPS]) causes a disruption in normal AA metabolism and increases visceral protein synthesis at the expense of muscle protein synthesis. The objective of this study was to determine the effect of supplemental dietary Leu on the dynamics of whole body nitrogen (N) retention in starter pigs before and after immune system stimulation (ISS) induced by LPS. A total of 28 starter pigs (14.46 ± 0.73 kg BW) were assigned to isoenergetic and isonitrogenous diets formulated to supply essential AA 10% above estimated requirements for maximum whole-body protein deposition (PD) and to contain increasing amounts of Leu: CON (1.36% SID Leu); LEU-M (2.04% SID Leu); and LEU-H (2.72% SID Leu). Pigs were housed in metabolic crates, scale-fed every 4 h based on BW, and adjusted to dietary treatments for 5 d. The 108-h N-balance experiment was divided into two periods: prechallenge (before LPS challenge; six 12-h collections) and challenge (after LPS challenge; three 12-h collections) periods. In both periods, blood was collected to determine plasma AA and urea N concentrations. At the start of the challenge period, one-half of the pigs fed CON and all pigs fed LEU-M and LEU-H were challenged with LPS (ISS+; 30 µg/kg injected intramuscularly); the remaining pigs fed CON were injected with saline (ISS-). Whole-body N retention was determined during subsequent 12-h collections. Plasma free Leu concentration increased linearly with increasing Leu content in the diet before LPS was administered (CON, 124 µmol/L; LEU-M, 185 µmol/L; LEU-H, 227 µmol/L; < 0.01). During the prechallenge period, N retention was lower in pigs fed LEU-M ( < 0.01) and there was no difference between pigs fed CON and LEU-H (7.91, 7.18, and 7.71 g/12 h for CON, LEU-M, and LEU-H, respectively). During the challenge period, N retention in pigs fed CON was higher in ISS- than ISS+ (5.37 vs. 3.83 g/12 h; < 0.01) but was not affected by diet in ISS+ pigs (3.83, 3.21, and 3.45 g/12 h for CON, LEU-M, and LEU-H, respectively; > 0.10). In healthy pigs, feeding a high excess of dietary Leu induced an anabolic response to compensate for reduced N retention that occurred in pigs fed an intermediate excess of dietary Leu. There was no effect of supplemental Leu on N retention in pigs after an LPS challenge.

Metabolic response to an inflammatory challenge in pigs divergently selected for residual feed intake

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, = 10, and high: RFI, = 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 ( < 0.01). Feed intake was less on d 1 than on the other days ( < 0.001), as was total AA plasma concentrations at fasted state ( < 0.05). Fasted concentrations of His ( = 0.06) and Trp ( = 0.05) tended to be less, those of Val were less ( < 0.05), and fed concentrations of Lys were increased ( < 0.05) on d 7 compared to d -1. Uremia was less on d 7 than on d -1 at fasted state ( < 0.05), whereas it did not vary at fed state ( 0.1). Fasted glucose and insulin plasma concentrations were stable across days ( 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 ( < 0.05). Total AA, Gln, Ile, Leu, Pro ( < 0.05), and hydroxyproline ( = 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 ( < 0.05). Citrulline ( < 0.05) and Met ( < 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 ( < 0.05). On d 8, liver and LM protein synthesis tended to be lower ( = 0.07 and 0.09, respectively) and liver calpain activity was greater ( = 0.07) in RFI than RFI pigs. Liver and LM proteasome did not differ between lines ( 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 ( 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.

The effect of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus challenge on growing pigs I: Growth performance and digestibility

Porcine reproductive and respiratory syndrome (PRRS) and porcine epidemic diarrhea (PED) are two diseases costly to the U.S. swine industry. The objective of this study was to determine the impact of PRRS virus and PED virus, alone or in combination, on growth performance, feed efficiency, and digestibility in grower pigs. Forty-two gilts (16 ± 0.98 kg BW) naïve for PRRS and PED were selected and allocated to 1 of 4 treatments. Treatments included 1) a control, 2) PRRS virus infected, 3) PED virus infected, and 4) PRRS+PED coinfection (PRP). Pigs in treatments 2 and 4 were inoculated with a live field strain of PRRS virus via intramuscular and intranasal routes at 0 d after inoculation (dpi). Treatments 3 and 4 were orally inoculated with a cloned PED virus at 15 dpi. Infection with PRRS virus was confirmed by quantitative PCR and seroconversion. Infection with PED virus was confirmed with PCR. Control pigs remained PRRS and PED virus negative throughout the study. All pigs were offered, ad libitum, a standard diet with free access to water. During the test period, PRRS reduced ADG and ADFI by 30 and 26%, respectively (P < 0.05), compared with control pigs, whereas PRP decreased ADG, ADFI, and G:F by 45, 30, and 23%, respectively (P < 0.05). Additional reductions in ADG and G:F were detected in PRP pigs compared with singular PED or PRRS treatments (33 and 16%, respectively). The impact of PED, alone or in combination, on performance (15–21 dpi) reduced ADG (0.66 vs. 0.35 vs. 0.20 kg/d; P < 0.01), ADFI (1.22 vs. 0.88 vs. 0.67 kg/d; P = 0.003), and G:F (0.54 vs. 0.39 vs. 0.31; P = 0.001) compared with control pigs. Compared with control pigs, PRRS infection did not reduce apparent total tract digestibility (ATTD) of nutrients and energy. However, PED infection, alone or in combination, decreased ATTD of DM and energy by 8 and 12%, respectively (P < 0.05). Compared with control pigs, PRP reduced N and OM ATTD by 13 and 3%, respectively (P < 0.05). No significant differences in apparent ileal digestibility (AID) were detected between virus challenges. However, Lys AID tended to be reduced in both PED treatments compared with the control (10 and 12%; P = 0.095). Altogether, PRRS reduced growth but did not alter digestibility. Pigs challenged with PED and, to a greater extent, the coinfection of PED and PRRS viruses had reduced ADG, ADFI, G:F, and ATTD of nutrients and energy.

The effect of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus challenge on growing pigs II: Intestinal integrity and function

The objective of this study was to determine if intestinal function and integrity is altered due to porcine reproductive and respiratory syndrome (PRRS) virus and porcine epidemic diarrhea (PED) virus infection in growing pigs. Forty-two gilts (16.8 ± 0.6 kg BW), naïve for PRRS and PED, were selected and randomly assigned to 1 of 4 treatments: 1) a control (CON; = 6), 2) PRRS virus challenge only (PRRS; = 12), 3) PED virus challenge only (; = 12), or 4) coinfection of PRRS + PED viruses (PRP; = 12). Treatments 2 and 4 were inoculated with a live field strain of PRRS virus on d 0 after inoculation. Treatments 3 and 4 were inoculated with PED virus on 14 d after inoculation (dpi) and all pigs were euthanized 7 d later (21 dpi). Infection with PRRS virus was determined by viremia and seroconversion. Fecal quantitative PCR was used to confirm PED virus infection. Control pigs remained PRRS and PED virus negative throughout the study. Compared with the CON, intestinal morphology was unaffected by PRRS. As expected, PED and PRP treatments resulted in duodenum, jejunum, and ileum villus atrophy compared with the CON treatment ( < 0.01). Ex vivo transepithelial electrical resistance (TER) did not differ between CON and PRRS pigs (P < 0.05) but was reduced by 40% in PED alone ( < 0.01). Interestingly, TER was increased ( < 0.01) in the PRP pigs. Active transport of glucose was increased in PRRS pigs over CON pigs ( < 0.01), whereas PED had pigs increased ( < 0.01) active glutamine transport over the CON pigs. Jejunum GLUT2 mRNA abundance and sucrase, maltase, and Na+/K+ adenosine triphosphatase activities tended to be increased in PRRS pigs compared with CON pigs ( < 0.06). The jejunum AA transporter, SLC6A14, and mucin 2 mRNA abundance tended to be increased in PED-only pigs ( < 0.10). These data suggest that PRRS infection supports a higher affinity for glucose uptake, whereas PED favors glutamine uptake. Interestingly, digestive machinery during PED challenge remained intact. Altogether, PED but not PRRS challenges alter intestinal morphology and integrity in growing pigs.

Pigs that are divergent in feed efficiency, differ in intestinal enzyme and nutrient transporter gene expression, nutrient digestibility and microbial activity

Feed efficiency is an important trait in the future sustainability of pig production, however, the mechanisms involved are not fully elucidated. The objective of this study was to examine nutrient digestibility, organ weights, select bacterial populations, volatile fatty acids (VFA's), enzyme and intestinal nutrient transporter gene expression in a pig population divergent in feed efficiency. Male pigs (n=75; initial BW 22.4 kg SEM 2.03 kg) were fed a standard finishing diet for 43 days before slaughter to evaluate feed intake and growth for the purpose of calculating residual feed intake (RFI). Phenotypic RFI was calculated as the residuals from a regression model regressing average daily feed intake (ADFI) on average daily gain (ADG) and midtest BW0.60 (MBW). On day 115, 16 pigs (85 kg SEM 2.8 kg), designated as high RFI (HRFI) and low RFI (LRFI) were slaughtered and digesta was collected to calculate the coefficient of apparent ileal digestibility (CAID), total tract nutrient digestibility (CATTD), microbial populations and VFA's. Intestinal tissue was collected to examine intestinal nutrient transporter and enzyme gene expression. The LRFI pigs had lower ADFI (P<0.001), improved feed conversion ratio (P<0.001) and an improved RFI value relative to HRFI pigs (0.19 v. -0.14 SEM 0.08; P<0.001). The LRFI pigs had an increased CAID of gross energy (GE), and an improved CATTD of GE, nitrogen and dry matter compared to HRFI pigs (P<0.05). The LRFI pigs had higher relative gene expression levels of fatty acid binding transporter 2 (FABP2) (P<0.01), the sodium/glucose co-transporter 1 (SGLT1) (P<0.05), the glucose transporter GLUT2 (P<0.10), and the enzyme sucrase-isomaltase (SI) (P<0.05) in the jejunum. The LRFI pigs had increased populations of lactobacillus spp. in the caecum compared with HRFI pigs. In colonic digesta HRFI pigs had increased acetic acid concentrations (P<0.05). Differences in nutrient digestibility, intestinal microbial populations and gene expression levels of intestinal nutrient transporters could contribute to the biological processes responsible for feed efficiency in pigs.

The Effect of Divergence in Feed Efficiency on the Intestinal Microbiota and the Intestinal Immune Response in Both Unchallenged and Lipopolysaccharide Challenged Ileal and Colonic Explants

Feed efficiency is an important trait in pig production, with evidence to suggest that the efficiencies of a variety of biological systems contribute to variation in this trait. Little work has been conducted on the contribution of the intestinal innate immune response to divergence in feed efficiency. Hence, the objective of this study was to examine select bacterial populations and gene expression profiles of a range of targets relating to gut health and immunity in the intestine of pigs phenotypically divergent in feed efficiency in: a) the basal state; and (b) following an ex-vivo lipopolysaccharide (LPS) challenge of ileal and colonic tissue. Male pigs (initial BW 22.4 kg (SD = 2.03)) were fed a standard finishing diet for the final 43 days prior to slaughter to evaluate feed intake and growth for the purpose of calculating residual feed intake (RFI). On day 115, 16 animals (average weight 85 kg, SEM 2.8 kg), designated high RFI (HRFI) and low RFI (LRFI) were slaughtered. The LRFI pigs had increased lactobacillus spp. in the caecum compared to HRFI pigs (P < 0.05). RFI groups did not differ in the expression of the measured genes involved in the innate immune system in the basal ileal or colonic tissues (P > 0.10). Interestingly, there was an interaction between RFI and LPS for the cytokines IL-8, IL-1, IL-6, TNF-α, Interferon-γ (IFN-γ) and SOCS3, with the LRFI group having consistently lower gene expression in the colon following the LPS challenge, compared to the HRFI group. The lower gene expression of SOCS and cytokines following an ex vivo LPS challenge supports the theory that a possible energy saving mechanism exists in the intestinal innate immune response to an immune challenge in more feed efficient pigs.

Fatty acids, inflammation and intestinal health in pigs

The intestine is not only critical for nutrient digestion and absorption, but also is the largest immune organ in the body. However, in pig production, inflammation induced by numerous factors, such as pathogen infection and stresses (e.g., weaning), results in intestinal mucosal injury and dysfunction, and consequently results in poor growth of pigs. Dietary fatty acids not only play critical roles in energy homeostasis and cellular membrane composition, but also exert potent effects on intestinal development, immune function, and inflammatory response. Recent studies support potential therapeutic roles for specific fatty acids (short chain and medium chain fatty acids and long chain polyunsaturated fatty acids) in intestinal inflammation of pigs. Results of these new lines of work indicate trophic and cytoprotective effects of fatty acids on intestinal integrity in pigs. In this article, we review the effect of inflammation on intestinal structure and function, and the role of specific fatty acids on intestinal health of pigs, especially under inflammatory conditions.

A review of feed efficiency in swine: biology and application

Feed efficiency represents the cumulative efficiency with which the pig utilizes dietary nutrients for maintenance, lean gain and lipid accretion. It is closely linked with energy metabolism, as the oxidation of carbon-containing components in the feed drive all metabolic processes. While much is known about nutrient utilization and tissue metabolism, blending these subjects into a discussion on feed efficiency has proven to be difficult. For example, while increasing dietary energy concentration will almost certainly increase feed efficiency, the correlation between dietary energy concentration and feed efficiency is surprisingly low. This is likely due to the plethora of non-dietary factors that impact feed efficiency, such as the environment and health as well as individual variation in maintenance requirements, body composition and body weight.

Nonetheless, a deeper understanding of feed efficiency is critical at many levels. To individual farms, it impacts profitability. To the pork industry, it represents its competitive position against other protein sources. To food economists, it means less demand on global feed resources. There are environmental and other societal implications as well.

Interestingly, feed efficiency is not always reported simply as a ratio of body weight gain to feed consumed. This review will explain why this arithmetic calculation, as simple as it initially seems, and as universally applied as it is in science and commerce, can often be misleading due to errors inherent in recording of both weight gain and feed intake.

This review discusses the importance of feed efficiency, the manner in which it can be measured and reported, its basis in biology and approaches to its improvement. It concludes with a summary of findings and recommendations for future efforts.

Short-term exposure to heat stress attenuates appetite and intestinal integrity in growing pigs

Acute heat stress (HS) and heat stroke can be detrimental to the health, well-being, and performance of mammals such as swine. Therefore, our objective was to chronologically characterize how a growing pig perceives and initially copes with a severe heat load. Crossbred gilts (n=32; 63.8±2.9 kg) were subjected to HS conditions (37°C and 40% humidity) with ad libitum intake for 0, 2, 4, or 6 h (n=8/time point). Rectal temperature (Tr), respiration rates (RR), and feed intake were determined every 2 h. Pigs were euthanized at each time point and fresh ileum and colon samples were mounted into modified Ussing chambers to assess ex vivo intestinal integrity and function. Transepithelial electrical resistance (TER) and fluorescein isothiocyanate-labeled dextran (FD4) permeability were assessed. As expected, Tr increased linearly over time (P<0.001) with the highest temperature observed at 6 h of HS. Compared to the 0-h thermal-neutral (TN) pigs, RR increased (230%; P<0.001) in the first 2 h and remained elevated over the 6 h of HS (P<0.05). Feed intake was dramatically reduced due to HS and this corresponded with significant changes in plasma glucose, ghrelin, and glucose-dependent insulinotropic peptide (P<0.050). At as early as 2 h of HS, ileum TER linearly decreased (P<0.01), while FD4 linearly increased with time (P<0.05). Colon TER and FD4 changed due to HS in quadratic responses over time (P=0.050) similar to the ileum but were less pronounced. In response to HS, ileum and colon heat shock protein (HSP) 70 mRNA and protein abundance increased linearly over time (P<0.050). Altogether, these data indicated that a short duration of HS (2-6 h) compromised feed intake and intestinal integrity in growing pigs.