Low Residual Feed Intake Line Research Articles

Physiological response to the weaning in two pig lines divergently selected for residual feed intake.

Breeding efficient pigs is a way to reduce dietary costs and environmental waste. However, optimization of feed efficiency must not be linked to a decrease of the ability of animals to cope with stress, such as the weaning. This study characterizes the response after weaning of pigs from two lines divergently selected for residual feed intake (RFI) during growth. Animals of the low (L) RFI line are more efficient than animals from the high (H) RFI line. Thirty-six piglets from each line weaned at 28days of age were individually housed and fed a conventional dietary sequence. Their performance, behaviour, health and oxidative status, immune and nutritional parameters were followed during three weeks. Daily feed intake and growth rate of pigs from the LRFI line were 35% and 40% lower compared with HRFI (p<0.001). Pigs from the LRFI-line had lower total tract apparent digestibility (-6% for OM) and suffered more from undernutrition with a 167 and 55% higher plasmatic concentration of NEFA and urea compared with HRFI (p<0.01). In the first week after the weaning, they had more diarrhoea and had a higher inflammatory status with concentration of haptoglobin 52% higher (p<0.001). These piglets then seemed to adapt to the weaning conditions and to recover during the second and third weeks. Both lines had similar zootechnical performance and physiological characteristics at the end of the post-weaning period. To conclude, the physiological responses to the weaning differed between lines. Pigs from the LRFI line, selected for greater feed efficiency, were more sensitive to the weaning stress. They were also more resilient as they finally adapted to the new condition and recovered to show similar performance results as pigs of the HRFI line.

Responses to weaning in two pig lines divergently selected for residual feed intake depending on diet.

Weaning is a stress every piglet has to face. It is a main cause of antibiotic uses due to digestive disorders. In this study, response to weaning was analyzed in pigs from two lines divergently selected for residual feed intake (RFI) during growth. A total of 132 pigs from each line, housed per line and diet in conventional postweaning units of 12 castrated males and 12 females, were fed either a conventional control (two successive diets) or a complex (three successive diets) dietary sequence during the postweaning period (4 to 10 wk of age). BWs were recorded at weaning (days 0 and 28 of age), days 1, 2, 6, 12, 19, 26, and 42 (10 wk of age), and at 23 wk of age. Feces texture was examined before weaning (day -1), at day 1, 2, 6, 12, and 19. Feed intake was recorded at pen level from days 0 to 42 after weaning, and individually thereafter. Plasma was collected after blood samplings at days -1, 6, 19, and 42 on half of the piglets: all piglets of a given sex in each pen were sampled, to achieve a balanced number across factors. Pigs of the low RFI (LRFI) line were heavier at weaning, had greater glucose concentration, and lower levels of diarrhea at days 1 and 2 than pigs from the high RFI (HRFI) line (P < 0.01). At day 42, there was no BW difference between lines, and G:F ratio did not differ between lines (P = 0.40). The LRFI pigs had lower feed intake and growth rate from day 0 to day 19 (P < 0.005), and greater plasma concentration of non-esterified fatty acid (P < 0.001), indicating an increased mobilization of body lipids and proteins immediately after weaning compared with HRFI pigs. They also had greater levels of diarrhea at day 6 (22% for LRFI vs. 14% for HRFI, P = 0.002), but the concentration of plasma haptoglobin did not indicate acute inflammation. The complex diet sequence improved feed intake and growth, and reduced diarrhea, mainly in the LRFI line (P < 0.001). To conclude, pigs from the LRFI line were more negatively affected by weaning stress, but managed to recover afterwards. The complex diet sequence ameliorated some of the negative effects that weaning had on the LRFI pigs, but limited effects of nursery period feeding sequence on growth performance were observed during the growing-finishing period.

Sélection pour la consommation alimentaire moyenne journalière résiduelle chez le porc : impacts sur les caractères et défis pour la filière

L’amélioration de l’efficacité alimentaire est un enjeu majeur pour la compétitivité de la filière porcine. Elle est classiquement mesurée en élevage par l’indice de consommation, indicateur économique de l’efficacité d’utilisation des aliments pour la croissance. Un critère alternatif indépendant des performances des animaux, la Consommation Moyenne Journalière Résiduelle (CMJR), a été proposé dans les années 1960. Cet article synthétise les résultats obtenus à partir de la sélection divergente de deux lignées à l’INRA, une lignée à CMJR faible, animaux consommant moins que prédit pour leurs besoins de production et d’entretien, et donc plus efficaces, et une lignée à CMJR élevée, animaux consommant plus que prédit pour leurs besoins, moins efficaces. Ces recherches montrent qu’il est possible de sélectionner pour la CMJR chez le porc en croissance avec un impact limité sur les caractères de production et de reproduction femelle, permettant ainsi de diminuer les quantités d’aliments utilisées en élevage. La dégradation des paramètres de qualité technologique de la viande en réponse à l’amélioration génétique de l’efficacité alimentaire est un point de vigilance dans les stratégies de sélection, de même que la composition nutritionnelle de la ration alimentaire. Finalement, la capacité de réponse à des stress ou à des changements de conditions d’élevage ne semble pas affectée par la sélection, contrairement à ce qui est suggéré dans la littérature en réponse à la sélection pour une CMJR réduite. Les défis qui résultent de ces résultats pour poursuivre l’amélioration de ce caractère en production tout en répondant à l’évolution des contraintes de l’élevage sont discutés.

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.

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

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

A transcriptome multi-tissue analysis identifies biological pathways and genes associated with variations in feed efficiency of growing pigs

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

Serpina3 and Vitronectin as Biomarkers for Feed Efficiency in Swine

ObjectivesFeed represents over 60% of cost inputs in pork production in the United States. Residual feed intake (RFI) is a measure of feed efficiency representing the difference between observed and expected feed intake based on average daily gain and backfat. Two lines of pigs demonstrating differences in RFI have been generated by nine generations of selection. In previous two dimensional- difference in gel electrophoresis (2D-DIGE) experiments, vitronectin and the serine proteinase inhibitor A3 (serpinA3) were observed to be increased in the more efficient low RFI line, which suggests that they could serve as potential biomarkers for feed efficiency. SerpinA3 has many biological roles, including inflammation response, immune function, and tumor suppression. Roles of vitronectin include blood homeostasis, thrombosis, and fibrosis. Our objective was to determine the extent to which selection for RFI influences serum serpinA3 and vitronectin abundance for pigs fed traditional versus alternative low energy, high fiber diets.Materials and MethodsPigs from the ninth generation of the Iowa State University RFI Project were used for this study. Serum samples were collected from pigs between 35 and 42 d of age and stored at –80°C. During finishing, pigs from both lines were fed either a standard corn-soybean diet or a low energy, high fiber diet until slaughter. Individual feed intake data was collected to calculate RFI. Pigs from each line and diet (n = 7/diet/line, total n = 28) were selected from a larger set of animals to represent the most extreme RFI values for each diet. One dimensional western blot analysis was performed on SDS-PAGE gels to determine the relative abundance of serpinA3 and vitronectin in the individual samples. Samples were run in duplicate against a pooled reference of all samples. Data were analyzed using the mixed procedure of SAS version 9.3, with gel included as a random effect.ResultsRFI line did not significantly affect SerpnA3 abundance in serum. For the high fiber diet, serpinA3 abundance was numerically increased in the low RFI line (high RFI = 0.84, low RFI = 0.98, ± 0.09, P = 0.11).When fed the alternate diet, vitronectin was more abundant in serum from pigs the low RFI line (high RFI = 0.95, low RFI = 1.28 ± 0.15, P = 0.04).ConclusionSerpinA3 and vitronectin have shown potential as robust biomarkers in past 2D-DIGE experiments. However, based on this experiment serpinA3 and vitronectin do not appear to be consistently viable as biomarkers across different diet treatments when analyzed using one-dimensional western blot analysis. Though the proposed biomarkers show some promise in the high fiber diet, no noticeable difference was seen between the lines within the traditional diet treatment. This inconsistency may be caused by the inability of western blot techniques to show post-translational changes in protein that would be observed in 2D-DIGE. Based on their known biological roles, serpinA3 and vitronectin may play a part in protein turnover and ultimately postmortem proteolysis. Dietary factors may influence the viability of biomarkers for feed efficiency. This information could play a role in determining future biomarkers and methods of analysis that may be used in the pork industry. Supported by AFRI Grant 2011–68004–30336.

Impact of selection for residual feed intake on production traits and behavior of mule ducks

A divergent selection experiment of Muscovy sires based on the residual feed intake (RFI) of their male mule progeny was initiated in 2009. Using electronic feeders, the aim of this study was to establish whether 3 generations of selection for RFI had an impact on feeding behavior traits and general behavior, and to examine its effect on liver and meat quality. Eighty mule ducks, issued from 8 Muscovy drakes per line with extreme RFI, were tested in a pen equipped with 4 electronic feeders. Feeding behaviors were recorded from 3 to 7 wk after hatching under ad libitum feeding conditions. Then animals were prepared for overfeeding with a 3-week period of restricted feeding, and overfed during 12 d before slaughter. The RFI was significantly lower in the low RFI line than in the high RFI line (−5.4 g/d, P = 0.0005) and daily feed intake was reduced both over the entire test period (−5 g/d, P = 0.049) and on a weekly basis (P = 0.006). Weekly and total feed conversion ratios were also significantly lower (−0.08, P = 0.03 and −0.06, P = 0.01, respectively). Low RFI ducks had more frequent meals, spent as much time eating as high RFI ducks, and their feeding rate was lower when analyzed at the wk level only. Additionally no significant correlation between feed efficiency and feeding behavior traits was evidenced, indicating only limited relationships between RFI and feeding patterns. Some differences in behavioral responses to stressors (open field test combined with a test measuring the response to human presence) suggested that a lower RFI is associated with less fearfulness. Selection for RFI had no effect on liver weight and quality and a slightly deleterious impact on meat quality (decreased drip loss and L*). Finally, low RFI animals had higher body weights after restricted feeding from wk 10 to wk 12 and after overfeeding than high RFI ducks. This suggests that selection for reduced RFI until 7 wk of age increases the feed efficiency up to slaughter.

The effect of selection for residual feed intake on scale-activity and scale-exit scores in Yorkshire gilts

The objectives of the present study were to use scale-activity and scale-exit scores to (1) determine the extent to which selection for improved residual feed intake (RFI) correlates with individual gilt temperament, (2) determine whether the timing of assessment affects the scores, and (3) determine whether gilts habituate to the process of weighing. To achieve these objectives, 192 grow–finish purebred Yorkshire gilts (39.7 ± 5.7 kg; 98 ± 6 days old) were utilised. Ninety-six gilts were from the 5th generation of a line selected for low residual feed intake (LRFI), and 96 gilts were from the 5th generation of a randomly selected control line (CRFI). Gilt activity and exit behaviour were scored on the weigh scale. The activity score was taken at two time points, namely, t = 0 (immediately on the back gate closing on the weight scale) and t = 15 (15 s later). Activity was assessed using a 5-point scoring system (1 = calm, minimal movement; 5 = continuous rapid movement and an escape attempt), and exit score was assessed using a 3-point scoring system (1 = no encouragement needed, full exit; 3 = encouragement needed). Gilts were weighed once every 2 weeks (each weighing considered a testing round) for a maximum of eight scores per gilt. Statistical differences were identified in all rounds for activity between genetic lines, except Rounds 2, 4 and 5. For both lines, gilt-activity scores decreased over rounds. The LRFI line began with a lower activity score (2.31 vs 2.65 ± 0.13), but did not experience as great of a drop in average score over rounds as did the CRFI gilts (0.62 vs 1.21). By the end of the trial, the CRFI gilts scored lower than the LRFI gilts. Activity was greater at t = 15 than at t = 0. Although timing affected the score, the pattern was similar, and so consistency will be more important than timing procedure. For exit scores, in Rounds 5 and 7, the LRFI line scored lower than the CRFI line, and there was a trend for the LRFI line to score lower in Round 6. Across all gilts, the mean exit score increased slowly throughout the trial. In conclusion, selection for lower RFI in purebred Yorkshires has an effect on activity score but this relationship is complex and warrants further research. The observation that gilts become habituated to the process of weighing supports the conclusion that the process is not aversive.

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.

Selection for productivity and robustness traits in pigs

Pig breeding programs worldwide continue to focus on both productivity and robustness. This selection emphasis has to be accompanied by provision of better-quality environments to pigs to improve performance and to enhance health and welfare of pigs. Definition of broader breeding objectives that include robustness traits in addition to production traits is the first step in the development of selection strategies for productivity and robustness. An approach has been presented which facilitates extension of breeding objectives. Post-weaning survival, maternal genetic effects for growth as an indicator of health status and sow mature weight are examples of robustness traits. Further, breeding objectives should be defined for commercial environments and selection indexes should account for genotype by environment interactions (GxE). Average performances of groups of pigs have been used to quantify the additive effects of multiple environmental factors on performance of pigs. For growth, GxE existed when environments differed by 60 g/day between groups of pigs. This environmental variation was observed even on well managed farms. Selection for improved health of pigs should focus on disease resistance to indirectly reduce pathogen loads on farms and on disease resilience to improve the ability of pigs to cope with infection challenges. Traits defining disease resilience may be based on performance and immune measures, disease incidence or survival rates of pigs. Residual feed intake is a trait that quantifies feed efficiency. The responses of divergent selection lines for residual feed intake to various environmental challenges were often similar or even favourable for the more efficient, low residual feed intake line. These somewhat unexpected results highlight the need to gain a better understanding of the metabolic differences between more or less productive pigs. These physiological differences lead to interactions between the genetic potential of pigs for productivity and robustness and the prevalence of specific environmental conditions.

Liver and skeletal muscle mitochondria proteomes are altered in pigs divergently selected for residual feed intake1,2

Animals selected for residual feed intake (RFI) can be used as a model to elucidate molecular explanations for differences in growth efficiency. The objective of this study was to determine the extent to which the protein profile and posttranslational modifications of mitochondria from skeletal muscle and liver relate to feed efficiency gains in pigs divergently selected for RFI. Mitochondria were isolated from the longissimus dorsi (LD) muscle and the liver from pigs (n = 9 each for the high and low RFI line; BW = 95.8 kg). Mitochondria protein profile differences were determined using two-dimensional difference in gel electrophoresis. Proteins were identified using electrospray ionization mass spectrometry. In the line comparison, the β subunit of ATP synthase, heat shock protein (HSP) 60, and HSP70, were identified as being increased in mitochondria from the liver of the low RFI line (23 to 50%; P < 0.1). These differences were not observed in the other comparisons. In the LD, proteins identified as being different between RFI phenotypes included HSP70 and subunit 1 of the cytochrome bc1 complex. These data indicate that genetic selection for RFI tends to result in a consistent change in mitochondrial protein profile. In contrast, classification by phenotype demonstrates that phenotypic differences in RFI are not specifically associated with alterations of the mitochondria protein profile.

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.

Divergent genetic selection for residual feed intake impacts mitochondria reactive oxygen species production in pigs1

The objective of this study was to determine the extent to which genetic selection for residual feed intake (RFI) impacts electron leakage and reactive oxygen species (ROS) production in mitochondria from muscle and liver tissue. Understanding how genetic selection for RFI impacts animal physiology and growth efficiency is of the utmost importance as the world population increases. Production efficiency is tied directly to energy use. Mitochondria were used in this study because they produce 90% of the ATP in the body and use a large majority of dietary energy. Mitochondria were isolated from both muscle and liver tissue from pigs genetically selected for RFI (n = 8 per RFI line; 34 ± 4 kg). A 2,7-dichlorofluorscein diacetate assay was used to detect differences in hydrogen peroxide production between the more efficient low RFI line and the less efficient high RFI line. Our hypothesis was that greater efficiency would be linked to less ROS production from the mitochondria. There was less ROS production in mitochondria from the white portion of the semitendinosus in the low RFI line compared with the high RFI line, when both NADH and Flavin Adenine Dinucleotide (FADH2) energy substrates were used (glutamate and succinate, respectively). Additionally, mitochondria from the red portion of the semitendinosus in the low RFI line had less ROS production when succinate was used as an energy substrate (P < 0.05). A positive correlation was observed between RFI and ROS in mitochondria from the LM. These data indicate genetic selection for RFI may influence mitochondrial ROS production and efficiency of pork production.

Selection for residual feed intake alters the mitochondria protein profile in pigs

Residual feed intake (RFI) is a production efficiency measurement used to account for the growth performance of an individual animal. Less efficient animals have greater levels of oxidative stress. A major source of in vivo oxidative stress is the mitochondria. In this study the protein profile of mitochondria was investigated to determine differences between pigs genetically selected for high and low RFI (less and more efficient, respectively). Mitochondria were isolated from the red and white portions of the semitendinosus muscle (STR and STW respectively), from the longissimus dorsi (LD) muscle, and the liver from pigs (n=24, 12 per line) genetically selected for low or high RFI. Mitochondrial protein differences between lines were determined using 2-D DIGE, and spots were identified using electrospray ionization mass spectroscopy. Heat shock protein (HSP) 60 and HSP70, which have been linked to anti-apoptotic pathways in the mitochondria, were increased in the low RFI line. Endoplasmic reticulum oxidase-1 α (ERO1α) was decreased in LD mitochondria from the low RFI line. The protein profile of mitochondria from the more efficient pigs indicates an increase in anti-oxidant defenses and potential modifications of metabolic pathways leading to oxidative stress, metabolism, and cellular repair. Observed shifts in the mitochondria protein profile indicate that pigs divergently selected for low residual feed intake (RFI) may be less prone to muscular oxidative stress, and the liver may have a greater metabolic capacity when compared to their less efficient high RFI contemporaries. Both oxidative stress and metabolic capacity are key areas of interest with regard to increasing the efficiency of pork production. Through the use of divergent selection for RFI and investigation of protein profile and other biological differences between RFI lines of pigs, it is possible to determine biological pathways that affect efficiency of food production.

Onset of puberty and early-life reproduction in Angus females divergently selected for post-weaning residual feed intake

Angus cattle that had been divergently selected for Low and High post-weaning residual feed intake (RFI) were used in two projects to evaluate early-life reproductive performance and onset of puberty in females. In the first project, data on the 1999-born females (n = 64) were evaluated for weight, subcutaneous fat (P8 fat depth) and reproductive performance over two breeding cycles. These females that were the result of 1.0–2.5 (mean of 1.8) generations of selection, had mean (±s.e.) post-weaning RFI of –0.82 ± 0.19 kg/day and 0.57 ± 0.18 kg/day for the Low and High RFI selection lines, respectively. In the second project, ultrasonography was used to scan the ovaries of the 2008-born heifers (n = 121) on four occasions following weaning. In these heifers the presence of corpus luteum provided evidence of ovulation, and hence the commencement of onset of puberty. The average of the estimated breeding value (EBV) for RFI of the parents of the Low RFI and the High RFI selection line heifers were –0.72 ± 0.05 and 0.37 ± 0.03 kg/day, respectively. In the first project, no significant selection line differences were evident for weight, age at first mating, pregnancy and calving rates (percentage of females that were pregnant, or the percentage that calved out of the total number used for mating), calf birthweight and weight of calf born per female exposed to bull. Females from the Low RFI line had significantly (P &lt; 0.05) lower P8 fat depth relative to their High RFI contemporaries at most of the measurement dates (e.g. 9.2 ± 0.5 versus 12.0 ± 0.5 mm at the start of first mating). Low RFI females also calved significantly (P &lt; 0.05) later in the calving season than High RFI females (35.7 ± 3.0 versus 27.6 ± 2.4 days). The results indicate that there is a delayed pregnancy date during the first mating season leading to a later calving date for the Low RFI heifers. The later first calving date was then maintained at subsequent calving. The later calving, however, did not impact on pregnancy and calving rates. In the second project, it was observed that irrespective of selection line, heifers that had attained onset of puberty had significantly (P &lt; 0.05) greater P8 fat depth than those that had not. Hence the expectation was that, relative to High RFI heifers, the Low RFI heifers with their lower P8 fat, will attain onset of puberty at a slightly older age. This expected trend was observed but the difference was not significant, and further investigations are recommended.

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.

A calcitonin receptor (CALCR) single nucleotide polymorphism is associated with growth performance and bone integrity in response to dietary phosphorus deficiency

Although concerns over the environmental impact of excess P in the excreta from pig production and governmental regulations have driven research toward reducing dietary supplementation of P to swine diets for over a decade, recent dramatic increases in feed costs have further motivated researchers to identify means to further reduce dietary P supplementation. We have demonstrated that genetic background impacts P utilization in young pigs and have identified genetic polymorphisms in several target genes related to mineral utilization. In this study, we examined the impact of a SNP in the calcitonin receptor gene (CALCR) on P utilization in growing pigs. In Exp. 1, 36 gilts representing the 3 genotypes identified by this CALCR SNP (11, 12, and 22) were fed a P-adequate (PA) or a marginally P-deficient (approximately 20% less available P; PD) diet for 14 wk. As expected, P deficiency reduced plasma P concentration, bone strength, and mineral content (P < 0.05). However, the dietary P deficiency was mild enough to not affect the growth performance of these pigs. A genotype x dietary P interaction (P < 0.05) was observed in measures of bone integrity and mineral content, with the greatest reduction in bone strength and mineral content due to dietary P deficiency being associated with the allele 1. In Exp. 2, 168 pigs from a control line and low residual feed intake (RFI) line were genotyped for the CALCR SNP and fed a PA diet. As expected, pigs from the low RFI line consumed less feed but also gained less BW when compared with the control line (P < 0.05). Although ADFI did not differ between genotypes, pigs having the 11 genotype gained less BW (P < 0.05) than pigs having the 12 or 22 genotypes. Pigs of the 11 and 12 genotypes had bones that tolerated greater load when compared with animals having the 22 genotype (P < 0.05). A similar trend was observed in bone modulus and ash % (P < 0.10). These data are supportive of the association of this CALCR SNP with bone integrity and its response to dietary P restriction. Although the allele 1 is associated with greater bone integrity and mineral content during adequate P nutrition, it is also associated with the greatest loss in bone integrity and mineral content in response to dietary P restriction. Understanding the underlying genetic mechanisms that regulate P utilization may lead to novel strategies to produce more environmentally friendly pigs.

Selection response and genetic parameters for residual feed intake in Yorkshire swine1

Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between the observed feed intake and that predicted from the average requirements for growth and maintenance. The objective of this study was to evaluate the response in a selection experiment consisting of a line selected for low RFI and a random control line and to estimate the genetic parameters for RFI and related production and carcass traits. Beginning with random allocation of purebred Yorkshire littermates, in each generation, electronically measured ADFI, ADG, and ultrasound backfat (BF) were evaluated during a approximately 40- to approximately 115-kg of BW test period on approximately 90 boars from first parity and approximately 90 gilts from second parity sows of the low RFI line. After evaluation of first parity boars, approximately 12 boars and approximately 70 gilts from the low RFI line were selected to produce approximately 50 litters for the next generation. Approximately 30 control line litters were produced by random selection and mating. Selection was on EBV for RFI from an animal model analysis of ADFI, with on-test group and sex (fixed), pen within group and litter (random), and covariates for interactions of on- and off-test BW, on-test age, ADG, and BF with generations. The RFI explained 34% of phenotypic variation in ADFI. After 4 generations of selection, estimates of heritability for RFI, ADFI, ADG, feed efficiency (FE, which is the reciprocal of the feed conversion ratio and equals ADG/ ADFI), and ultrasound-predicted BF, LM area (LMA), and intramuscular fat (IMF) were 0.29, 0.51, 0.42, 0.17, 0.68, 0.57, and 0.28, respectively; predicted responses based on average EBV in the low RFI line were -114, -202, and -39 g/d for RFI (= 0.9 phenotypic SD), ADFI (0.9 SD), and ADG (0.4 SD), respectively, and 1.56% for FE (0.5 SD), -0.37 mm for BF (0.1 SD), 0.35 cm(2) for LMA (0.1 SD), and -0.10% for IMF (0.3 SD). Direct phenotypic comparison of the low RFI and control lines based on 92 low RFI and 76 control gilts from the second parity of generation 4 showed that selection had significantly decreased RFI by 96 g/d (P = 0.002) and ADFI by 165 g/d (P < 0.0001). The low RFI line also had 33 g/d lower ADG (P = 0.022), 1.36% greater FE (P = 0.09), and 1.99 mm less BF (P = 0.013). There was not a significant difference in LMA and other carcass traits, including subjective marbling score, despite a large observed difference in ultrasound-predicted IMF (-1.05% with P < 0.0001). In conclusion, RFI is a heritable trait, and selection for low RFI has significantly decreased the feed required for a given rate of growth and backfat.