High RFI Pigs Research Articles

Response of pigs divergently selected for residual feed intake to experimental infection with the PRRS virus

Feed efficiency is of great importance to the swine industry, yet few studies have evaluated the robustness of pigs selected for increased feed efficiency based on residual feed intake (RFI) when challenged with disease. RFI is calculated as the difference between the observed and expected feed intake. The objective of this study was to assess the effect of porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) infection on lines of pigs divergently selected for RFI. Hypothesizing that the more feed efficient low RFI (LRFI) pigs would be more affected by PRRSV-infection, 97 piglets from LRFI and 99 piglets from high RFI (HRFI) selection lines were experimentally infected with the NVSL 97-7985 PRRSV isolate 1 to 3 weeks post-weaning. Pig body weight was recorded weekly and used to calculate average daily gain (ADG). For comparison, ADG was also evaluated on 489 non-challenged LRFI and HRFI pigs housed in a separate facility. Viral load (VL) was quantified as area under the curve for 0–21 days post-infection (dpi) of the log of PCR-based serum viremia. Antibody level was analyzed from serum samples collected at 4, 7, and 11 dpi by PRRS ELISA and MAGPIX assays to quantify PRRSV-specific IgG antibody and total antibody, respectively, during the early stages of PRRSV-infection. There was a tendency for pigs from the LRFI line to have lower VL (P=0.09), greater ADG (P=0.10), and be more likely to survive the PRRSV-challenge (P=0.06) than pigs from the HRFI line. However, joint analysis of challenged and non-challenged pigs showed a significant interaction between RFI line and challenge status (P=0.04), which demonstrated that growth of the LRFI line was less affected by PRRSV-challenge than growth of the HRFI line. Additionally, a significant interaction between RFI line and dpi for the ELISA (P<0.001) and MAGPIX (P=0.007) assays indicated that the increase in antibody levels from 7 to 11 dpi was greater for the LRFI line than for the HRFI line. In conclusion, the line selected for increased feed efficiency based on RFI (LRFI line) had greater growth under challenge and was therefore less affected by the PRRSV-challenge than the line selected for reduced efficiency (HRFI line). This suggests that the pigs selected for reduced RFI were more robust to the viral challenge.

Feed efficiency effects on barrow and gilt behavioral reactivity to novel stimuli tests.

Increasing feed efficiency is an important goal for improving sustainable pork production and profitability for producers. To study feed efficiency, genetic selection based on residual feed intake (RFI) was used to create 2 divergent lines. Low-RFI pigs consume less feed for equal weight gain compared to their less efficient, high-RFI counterparts. Therefore, our objective was to assess how a pig's behavioral reactivity toward fear-eliciting stimuli related to RFI selection and improvement of feed efficiency. In this study, behavioral reactivity of pigs divergently selected for RFI was evaluated using human approach (HAT) and novel object (NOT) tests. Forty low-RFI and 40 high-RFI barrows and gilts ( = 20 for each genetic line; 101 ± 9 d old) from ninth-generation Yorkshire RFI selection lines were randomly selected and evaluated once using HAT and once using NOT over a 2-wk period utilizing a crossover experimental design. Each pig was individually tested within a 4.9 × 2.4 m test arena for 10 min; behavior was evaluated using live and video observations. The test arena floor was divided into 4 zones; zone 1 being oral, nasal, and/or facial contact with the human (HAT) or orange traffic cone (NOT) and zone 4 being furthest from the human or cone and included the point where the pig entered the arena. During both HAT and NOT, low-RFI pigs entered zone 1 less frequently compared to high-RFI pigs ( ≤ 0.03). During NOT, low-RFI pigs changed head orientation more frequently ( = 0.001) but attempted to escape less frequently (low-RFI = 0.97 ± 0.21 vs. high-RFI = 2.08 ± 0.38; = 0.0002) and spent 2% less time attempting to escape compared to high-RFI pigs ( = 0.04). Different barrow and gilt responses were observed during HAT and NOT. During HAT, barrows spent 2% more time within zone 1 ( = 0.03), crossed fewer zone lines ( < 0.0001), changed head orientation less frequently ( = 0.002), and froze less frequently compared to gilts ( = 0.02). However, during NOT, barrows froze more frequently ( = 0.0007) and spent 2% longer freezing ( = 0.05). When the behavior and RFI relationship was examined using odds ratios, decreasing RFI by 1 kg/d decreased the odds of freezing by 4 times but increased the odds of attempting to escape by 5.26 times during NOT ( ≤ 0.04). These results suggest that divergent selection for RFI resulted in subtle behavioral reactivity differences and did not impact swine welfare with respect to responses to fear-eliciting stimuli.

Effects of genetic selection for residual feed intake on behavioral reactivity of castrated male pigs to novel stimuli tests

Increasing feed efficiency in swine is important for increasing sustainable food production and profitability for producers; therefore, this is often selected for at breeding. Residual feed intake (RFI) can be used for the genetic selection of pigs for feed efficiency. In our selection project, low-RFI pigs consume less feed for equal weight gain compared to their less efficient, high-RFI counterparts. However, little is known about how feed efficiency influences the pig's behavioral reactivity toward fear-eliciting stimuli. In this study, behavioral reactivity of pigs divergently selected for RFI was evaluated using human approach- (HAT) and novel object tests (NOT). Forty low-RFI (more feed efficient) and 40 high-RFI (less feed efficient) castrated male pigs (barrows; 46.5±8.6kg) from 8th generation Yorkshire RFI selection lines were randomly selected and evaluated once using HAT and once using NOT over a four week period utilizing a crossover experimental design. Each pig was individually tested within a 4.9×2.4m test arena for 10min; behavior was evaluated using live and video observations. The test arena floor was divided into four zones; zone 1 being oral, nasal, and/or facial contact with the human (HAT) or orange traffic cone (NOT) and zone 4 being furthest from the human or cone and included the point where the pig entered the arena. During both HAT and NOT, low-RFI pigs crossed fewer zones (P<0.0001), had fewer head movements (P≤0.02), defecated less frequently (P≤0.03), displayed a shorter duration of freezing (P=0.05), and froze less frequently (HAT: low-RFI=4.9±0.65 vs. high-RFI=7.5±0.96; NOT: low-RFI=4.7±0.66 vs. high-RFI=7.2±0.96; P<0.0001) compared to high-RFI pigs. During HAT, low-RFI pigs also attempted to escape less frequently (low-RFI=0.4±0.14 vs. high-RFI=1.1±0.30; P=0.001) compared to high-RFI pigs. In contrast, compared to the high-RFI pigs, low-RFI pigs took 48s longer during HAT and 52s longer during NOT to approach zone 1 (P≤0.04). These results indicate that low-RFI pigs had decreased behavioral reactivity during HAT and NOT compared to high-RFI pigs. This may suggest that reducing a pig's behavioral reactivity is an important component of improving feed efficiency; however, it may have implications for animal handling and facility design.

Difference in short-term responses to a high-fiber diet in pigs divergently selected for residual feed intake1

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

Improved nutrient digestibility and retention partially explains feed efficiency gains in pigs selected for low residual feed intake1

Residual feed intake (RFI) is a unique measure of feed efficiency (FE) and an alternative to traditional measures. The RFI is defined as the difference between the actual feed intake of a pig and its expected feed intake based on a given amount of growth and backfat. Therefore, selecting pigs with a low RFI (LRFI) results in a more feed-efficient animal for a given rate of growth. Our objective was to determine the extent to which apparent total tract digestibility of nutrients and energy use and retention may explain FE differences between pigs divergently selected for LRFI or high RFI (HRFI). After 7 generations of selection, 12 HRFI and 12 LRFI pigs (62 ± 3 kg BW) were randomly assigned to metabolism crates. Pigs had free access to a standard diet based on corn (Zea mays) and soybean (Glycine max) meal containing 0.4% TiO(2), an exogenous digestibility marker. After a 7-d acclimation, total urine and feces were collected for 72 h. Nutrient and energy digestibility, P digestibility, and N balance were then measured and calculated to determine differences between the RFI lines. As expected, ADFI was lower (2.0 vs. 2.6 kg; P < 0.01), ADG did not differ, and FE was higher in the LRFI (P < 0.001) compared to the HRFI pigs. The digestibility values for DM (87.3 vs. 85.9%), N (88.3 vs. 86.1%), and GE (86.9 vs. 85.4%) were higher (P ≤ 0.003) in the LRFI vs. HRFI pigs, respectively. The DE (16.59 vs. 16.32 MJ/kg DM) and ME (15.98 vs. 15.72 MJ/kg DM) values were also greater (P < 0.001) in LRFI pigs. When correcting for ADFI, P digestibility did not differ between the lines. However, the LRFI pigs tended to have improved N retention (P = 0.08) compared to HRFI pigs (36.9 vs. 32.1 g/d). In conclusion, the higher energy and nutrient digestibility, use, and retention may partially explain the superior FE seen in pigs selected for LRFI.

Protein profile in mitochondria of pigs selected for residual feed intake

The efficiency nutrients utilization depends partially on mitochondrial efficiency and function. Additionally, mitochondria are a prime source of reactive oxygen species. The purpose of this study was to compare mitochondria protein profile in pigs (n = 11 per line) divergently selected for feed efficiency (low or high residual feed intake, RFI). Mitochondria were freshly isolated from the longissimus dorsi muscle by differential centrifugation, leaving an enriched mitochondria pellet. The pellets were solubilized and 2D‐Differential In Gel Electrophoresis, pH 3–10 11cm strips in the first dimension and 12.5 % acrylamide gels in the second dimension, were performed. Proteins were identified by electrospray mass spectrometry (ESI/MS). ERO1α was found to be increased in high RFI pigs (P = 0.073). ERO1α impacts mitochondria permeability transition pore through production of reactive oxygen species. SLC41a2, a Mg transporter, was increased (P = 0.13), possibly impacting superoxide dismutase conversion of superoxide to hydrogen peroxide. Cytochrome P450 4A11, a potential source of oxidative stress, was found to be increased (P = 0.14) in high RFI pigs. These data tend to indicate less efficient, high RFI, pigs may be more prone to intracellular oxidative stress than low RFI pigs. This research was supported by USDA‐AFRI grant# 2010‐65206‐20670.

Muscle characteristics and meat quality traits are affected by divergent selection on residual feed intake in pigs1

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

Leptin mediates discriminate response to feed restriction in feed efficient pigs

Genetic mechanisms that control feed efficiency (FE) and feed intake are not well understood. Residual feed intake (RFI) is a measure of FE, in which low RFI designates high FE. Transcriptional profiling coupled with serum metabolite analyses were used to identify genes and pathways that respond to a feed restriction (FR) in high or low RFI pigs. Low RFI (n=10) and high RFI Yorkshire pigs (n=10) of ~82 kg were fed ad lib. or fed 80% of maintenance for 7 days in a 2x2 factorial treatment design. Microarray analysis declared 6,114 genes in fat and 305 genes in liver as differentially expressed (DE) in response to FR and 311 fat genes and 147 liver genes due to RFI. Functional annotation of DE genes due to RFI in fat indicates that pathways such as K+ transport and monocarboxylic acid metabolism were overrepresented. Genes that were DE due to FR in fat overrepresented many pathways, including TCA cycle, apoptosis, and MAPK signaling. Concentrations of serum T3 and glucose were higher in the low RFI vs. high RFI pigs. Serum leptin concentration was decreased by FR in high RFI pigs but had the opposite effect in low RFI pigs. Leptin expression was 2.4‐fold down‐regulated in the low RFI pigs and in silico pathway analysis indicates that leptin had the highest number of interacting neighbors among genes that were DE due to RFI in fat. Leptin may play a key role in determining pathways that respond to FR in feed efficient pigs. USDA‐NRI‐2005‐3560415618