Quantitative trait loci analysis on Sus scrofa chromosome 7 for meat production, meat quality, and carcass traits within a Duroc purebred population

Many QTL analyses related to meat production and meat quality traits have been carried out using an F(2) resource population produced by crossing 2 genetically different breeds. This experiment was intended to investigate whether these QTL were segregating in a purebred Duroc population that had been selected for meat production and meat quality traits during 7 generations. Sus scrofa chromosome 7, for which significant QTL of intramuscular fat and many other traits have already been reported, was studied. The polymorphism of 10 microsatellite markers that were arranged at about 20-cM intervals was investigated on 1,004 pigs. In the selected population, 954 progeny were produced from mating of 99 sires and 286 dams. The QTL analysis for a full-sib family population was examined with the multigeneration pedigree structure of the population. Variance component analysis was used to detect QTL in this population and was examined for the multigeneration pedigree population. In this study, multigenerational pedigree estimated identical by descent coefficients among sibs were produced using Markov chain Monte Carlo methods. The maximum likelihood of odds score was found at the 70-cM position for the LM area, at the 0-cM position for the pork color standard, and at the 120-cM position for the number of thoracic vertebra, but no significant QTL for intramuscular fat were detected on SSC 7. These results indicate that QTL analysis via a variance component method within a purebred population was effective to determine that QTL were segregating in a population of purebred Durocs.     

Quantitative trait locus mapping in an F2 Duroc x Pietrain resource population: II. Carcass and meat quality traits

Pigs from the F(2) generation of a Duroc x Pietrain resource population were evaluated to discover QTL affecting carcass composition and meat quality traits. Carcass composition phenotypes included primal cut weights, skeletal characteristics, backfat thickness, and LM area. Meat quality data included LM pH, temperature, objective and subjective color information, marbling and firmness scores, and drip loss. Additionally, chops were analyzed for moisture, protein, and fat composition as well as cook yield and Warner-Bratzler shear force measurements. Palatability of chops was determined by a trained sensory panel. A total of 510 F(2) animals were genotyped for 124 microsatellite markers evenly spaced across the genome. Data were analyzed with line cross, least squares regression interval, mapping methods using sex and litter as fixed effects and carcass weight or slaughter age as covariates. Significance thresholds of the F-statistic for single QTL with additive, dominance, or imprinted effects were determined on chromosome- and genome-wise levels by permutation tests. A total of 94 QTL for 35 of the 38 traits analyzed were found to be significant at the 5% chromosome-wise level. Of these 94 QTL, 44 were significant at the 1% chromosome-wise, 28 of these 44 were also significant at the 5% genome-wise, and 14 of these 28 were also significant at the 1% genome-wise significance thresholds. Putative QTL were discovered for 45-min pH and pH decline from 45 min to 24 h on SSC 3, marbling score and carcass backfat on SSC 6, carcass length and number of ribs on SSC 7, marbling score on SSC 12, and color measurements and tenderness score on SSC 15. These results will facilitate fine mapping efforts to identify genes controlling carcass composition and meat quality traits that can be incorporated into marker-assisted selection programs to accelerate genetic improvement in pig populations.     

Identification of quantitative trait loci for carcass composition and pork quality traits in a commercial finishing cross

A QTL study for carcass composition and meat quality traits was conducted on finisher pigs of a cross between a synthetic Piétrain/Large White boar line and a commercial sow cross. The mapping population comprised 715 individuals evaluated for a total of 30 traits related to growth and fatness (4 traits), carcass composition (11 traits), and meat quality (15 traits). Offspring of 8 sires (n = 715) were used for linkage analysis and genotyped for 73 microsatellite markers covering 14 chromosomal regions representing approximately 50% of the pig genome. The regions examined were selected based on previous studies suggesting the presence of QTL affecting carcass composition or meat quality traits. Thirty-two QTL exceeding the 5% chromosome-wise significance level were identified. Among these, 5 QTL affecting 5 different traits were significant at the 1% chromosome-wise level. The greatest significance levels were found for a QTL affecting loin weight on SSC11 and a QTL with an effect on the Japanese color scale score of the loin on SSC4. About one-third of the identified QTL were in agreement with QTL previously reported. Results showed that QTL affecting carcass composition and meat quality traits segregated within commercial lines. Use of these results for marker-assisted selection offers opportunities for improving pork quality by within-line selection.     

Evaluation of approaches to detect quantitative trait loci for growth, carcass, and meat quality on swine chromosomes 2, 6, 13, and 18. I. Univariate outbred F2 and sib-pair analyses

Results from univariate outbred F2 interval mapping and sib-pair analyses of 12 growth and 28 carcass traits to identify QTL on SSC 2, 6, 13, and 18 were compared. Phenotypic and genetic data were recorded on a three-generation resource population including 832 F2 pigs from a cross between three Berkshire sires and 18 Duroc dams. Thirty markers with an average spacing of approximately 16 cM were genotyped across the four chromosomes. The outbred F2 mixed model included the effects of sex, birth month, and year, one-QTL additive, dominance and imprinting coefficients calculated every 1 cM using interval mapping, and a random family effect. The general sib-pair model used to describe the phenotypic differences between sib-pairs included the same systematic and random effects and a one-QTL additive coefficient calculated every 1 cM. The outbred F2 analysis found significant evidence of QTL on SSC 2 associated with 105-d weight, backfat thicknesses, LM area, fat percent, shear force, juiciness, marbling, and tenderness. In addition, QTL were identified on SSC 6 relating to 42-d weight and LM area, and on SSC 18 for fat and moisture percents. In most instances, the outbred F2 approach offered greater power to detect QTL; however, the sib-pair analysis offered greater power in several instances. The trait-specific superiority could be due to the relative advantage of each model within a trait data set. The two approaches provided complementary evidence for QTL segregating between the Berkshire and Duroc breeds used in the study that may be used to aid marker-assisted introgression and selection and candidate gene studies to improve swine growth and meat quality characteristics.     

Effect of VRTN gene polymorphisms on Duroc pig production and carcass traits,and their genetic relationships

The thoracic vertebral number is associated with body length and carcass traits, and represents one of the most important traits in the pig industry. Recent studies have shown that vertnin (VRTN) gene is associated with variations in the vertebral number in commercial European pigs. However, the genetic relationships and effect of this VRTN gene in pig production and carcass traits remain uncertain. Therefore, we investigated the genetic relationships among traits such as vertebral numbers, carcass weight and length‐related traits, and meat production traits, and the effect of VRTN gene polymorphisms on these traits in a Duroc purebred population selected for its meat production traits. Highly positive genetic correlations were obtained between the thoracic vertebral numbers and length‐related traits (0.56 to 0.84), whereas low correlations were obtained with production traits and carcass weight (?0.16 to 0.05). VRTN gene polymorphisms indicated that the number of thoracic vertebrae and length‐related traits were significantly associated with the VRTN genotype, but had no significant effect on production traits and carcass weight. The results indicate that VRTN gene may be used as an effective selection marker to obtain pigs with high thoracic vertebral numbers and length‐related traits, without adversely affecting meat production traits.     

Quantitative trait loci analysis for growth and carcass traits in a Meishan x Duroc F2 resource population

We constructed a pig F2 resource population by crossing a Meishan sow and a Duroc boar to locate economically important trait loci. The F2 generation was composed of 865 animals (450 males and 415 females) from four F1 males and 24 F1 females and was genotyped for 180 informative microsatellite markers spanning 2,263.6 cM of the whole pig genome. Results of the genome scan showed evidence for significant quantitative trait loci (<1% genomewise error rate) affecting weight at 30 d and average daily gain on Sus scrofa chromosome (SSC) 6, carcass yield on SSC 7, backfat thickness on SSC 7 and SSC X, vertebra number on SSC 1 and SSC 7, loin muscle area on SSC 1 and SSC 7, moisture on SSC 13, intramuscular fat content on SSC 7, and testicular weight on SSC 3 and SSC X. Moreover, 5% genomewise significant QTL were found for birth weight on SSC 7, average daily gain on SSC 4, carcass length on SSC 6, SSC 7, and SSC X and lightness (L value) on SSC 3. We identified 38 QTL for 28 traits at the 5% genomewise level. Of the 38 QTL, 24 QTL for 17 traits were significant at the 1% genomewise level. Analysis of marker genotypes supported the breed of origin results and provided further evidence that a suggestive QTL for circumference of cannon bone also was segregating within the Meishan parent. We identified genomic regions related with growth and meat quality traits. Fine mapping will be required for their application in introgression programs and gene cloning.     

Validation of the QTL on SSC4 for meat and carcass quality traits in a commercial crossbred pig population

Porcine chromosome 4 harbours many quantitative trait loci (QTL) affecting meat quality, fatness and carcass composition traits, detected in resource pig populations previously. However, prior to selection in commercial breeds, QTL identified in an intercross between divergent breeds require confirmation, so that they can be segregated. Consequently, the objective of this study was to validate several QTL on porcine chromosome 4 responsible for meat and carcass quality traits. The experimental population consisted of 14 crossbred paternal half-sib families. The region of investigation was the q arm of SSC4 flanked by the markers S0073 and S0813. Regression analysis resulted in the validation of three QTL within the interval: Minolta a * loin, back fat thickness and the weight of trimmed ham. The results were additionally confirmed by factor analysis. Candidate genes were proposed for meat colour, which was the most evident QTL validated in this study.     

基于选择信号分析揭示猪终端父本群体间性状趋同的关键基因

【目的】试验旨在揭示终端父本皮特兰猪与杜洛克猪在人工选择作用下重要经济性状呈现出表型趋同的基因组变化特征。【方法】利用376头皮特兰猪、451头杜洛克猪品系Ⅰ、841头杜洛克猪品系Ⅱ和497头杜洛克猪品系Ⅲ群体的50K SNP芯片数据,以100 kb窗口、50 kb步长计算综合单倍型评分(iHS)和等位基因频率差(△AF),分别取前5%作为猪群体内、群体间的基因组选择信号候选区域;利用bedtools分别对iHS、△AF按照左右200 kb进行合并,每2个群体间合并后的iHS、△AF统计量的重叠区域定义为性状趋同区域,并挖掘该区域与猪重要经济性状相关的平行选择信号。【结果】iHS结果显示,在皮特兰猪和杜洛克猪4个群体内共检测到5 112个选择信号候选区域,总长约487.51 Mb。基于△AF方法,于皮特兰猪和杜洛克猪每2个群体间共检测到9 579个选择信号显著区域,总长约913.50 Mb。基于合并后的iHS和△AF,共检测到52个性状趋同区域,总长约4.67 Mb,注释到88个与猪的繁殖、胴体和肉质等性状相关的平行选择候选基因。【结论】皮特兰猪和杜洛克猪群体间存在性状趋同的基因组选择区域有52个,平行选择信号主要涉及猪的繁殖、胴体及肉质等重要经济性状,这与瘦肉型猪种相同的育种方向相关,这些关键基因的发现可为后续商业猪品种遗传改良提供参考。     

Exclusion of the swine leukocyte antigens as candidate region and reduction of the position interval for the Sus scrofa chromosome 7 QTL affecting growth and fatness

Pig chromosome 7 (SSC 7) has been shown to be rich in QTL affecting performance and quality traits. Most studies mapped the QTL close to the swine leukocyte antigens (SLA), which has a large effect on adaptability and natural selection. Previous comparative mapping studies suggested that the 15-cM region limited by markers LRA1 (mapped at 55 cM) and S0102 (mapped at 70 cM) contains hundreds of genes. To decrease the number of candidate genes, we improved the mapping resolution with a genetic chromosome dissection through a backcross recombinant progeny test program between Meishan (MS) and European (EU; i.e., Large White or Landrace) breeds. Three first-generation backcross--(EU x MS) x EU--and two second-generation backcross--([EU x MS] x EU) x EU--sires carrying a recombination in the QTL mapping interval were progeny-tested (i.e., measured for a total of 44 growth, fatness, carcass and meat quality traits). Progeny family size varied from 29 to 119 pigs. Animals were genotyped for markers covering the region of interest. Progeny-test results allowed the QTL interval to be decreased from 15 to 20 cM down to 10 cM, and even less than 6 cM if we assumed that the EU pigs used in this study share only one QTL allele. Except for a putative QTL affecting some carcass composition traits, the SLA is excluded as a candidate region, suggesting that it might be possible to apply a marker-assisted selection strategy for this QTL, while controlling SLA allele diversity. The strong QTL effects remaining in animals with only 12.5% (issued from first-generation backcross boars) and 6.25% (issued from second-generation back-cross boars) Meishan genetic background shows that epistatic interactions are likely to be limited. Finally, the QTL does not have strong effects on meat quality traits.     

Identification of carcass and meat quality quantitative trait loci in a Landrace pig population selected for growth and leanness

The identification of QTL related to production traits that are relevant for the pig industry has been mostly performed by using divergent crosses. The main objective of the current study was to investigate whether these growth, fatness, and meat quality QTL, previously described in diverse experimental populations, were segregating in a Landrace commercial population selected for litter size, backfat thickness, and growth performance. We have found QTL for carcass weight (posterior P > 0.75), cutlet weight (posterior P > 0.99), weight of ham (posterior P > 0.75), shoulders weight (posterior probability > 0.99), and shear firm-ness (posterior P > 0.99) on pig Chromosome 2. Moreover, QTL with posterior P > 0.75 for fat thickness between the 3rd and 4th ribs (Chromosome 7), rib weights (Chromosome 8), backfat thickness (Chromosomes 8, 9, and 10), and b Minolta color component (Chromosome 7) were identified. These results indicate that commercial purebred populations retain a significant amount of genetic variation, even for traits that have been selected for many generations.     

Identification of quantitative trait loci affecting corpora lutea and number of teats in a Meishan x Duroc F2 resource population

Understanding of the genetic control of female reproductive performance in pigs would offer the opportunity to utilize natural variation and improve selective breeding programs through marker-assisted selection. The Chinese Meishan is one of the most prolific pig breeds known, farrowing 3 to 5 more viable piglets per litter than Western breeds. This difference in prolificacy is attributed to the Meishan's superior prenatal survival. Our study utilized a 3-generation resource population, in which the founder grandparental animals were purebred Meishan and Duroc pigs, in a genome scan for QTL. Grandparent, F1, and F2 animals were genotyped for 180 microsatellite markers. Reproductive traits, including number of corpora lutea (number of animals = 234), number of fetuses per animal (n = 226), number of teats (n = 801), and total number born (n = 288), were recorded for F2 females. Genome-wide significance level thresholds of 1, 5, and 10% were calculated using a permutation approach. We identified 9 QTL for 3 traits at a 10% genome-wise significance level. Parametric interval mapping analysis indicated evidence of a 1% genome-wise significant QTL for corpora lutea on SSC 3. Nonparametric interval mapping for number of teats found 4 significant QTL on chromosomes SSC3 (P < 0.01), SSC7 (P < 0.01), SSC8 (P < 0.01), and SSC12 (P < 0.05). Partial imprinting of a QTL affecting teat number (P < 0.10) was detected on SSC8. Using the likelihood-ratio test for a categorical trait, 2 QTL for pin nipples were detected on SSC2 and SSC16 (P < 0.01). Fine mapping of the QTL regions will be required for their application to introgression programs and gene cloning.     

不同猪种5-羟色胺受体基因的表达及其与肉质的相关性分析

为研究5-羟色胺（5-HT）受体基因在不同猪种的表达及其与肉质的关系,试验选取淳安花猪与杜长大三元猪各12头,同时饲喂,达上市体重时分别屠宰,测定胴体、肉质性状及肌肉、脂肪中的5-HT受体基因表达量。结果表明：淳安花猪、杜长大三元猪的平均屠宰体重分别为88.1、102.4kg;淳安花猪的板油率、背膘厚、肌内脂肪等指标均显著高于杜长大三元猪（P〈0.05）;屠宰率、眼肌面积杜长大三元猪显著高于淳安花猪（P〈0.05）。5-HT2A、5-HT7受体基因在2个猪种脂肪组织中的表达量均显著高于肌肉组织（P〈0.05）,杜长大三元猪的肌肉中5-HT2A、5-HT7表达量显著低于淳安花猪（P〈0.05）,而脂肪中表达量两猪种间差异不显著。5-HT2A、5-HT7受体基因表达量与屠宰肉质指标之间基本呈负相关,尤其是肌肉中的5-HT2A表达量,呈较强负相关（杜长大三元猪）或显著负相关（淳安花猪）。研究初步认为,5-HT受体基因在中外猪种之间存在表达差异,并与屠宰肉质性状具有相关性。     

Quantitative trait locus mapping for meat quality traits in an Iberian x Landrace F2 pig population

An experimental F2 cross between Iberian and Landrace pig strains was performed to map quantitative trait loci (QTL) for diverse productive traits. Here we report results for meat quality traits from 369 F2 animals with records for pH 24 h postmortem (pH 24 h), muscle color Minolta measurements L* (lightness), a* (redness), and b* (yellowness), H* (hue angle), C* (chroma), intramuscular fat (IMF) and haematin pigment content measured in the longissimus thoracis. Pigs were genotyped for 92 markers covering the 18 porcine autosomes (SSC). Results of the genome scan show evidence for QTL for IMF (SSC6; F = 27.16), pH 24 h (SSC3; F = 7.73), haematin pigments (SSC4 and SSC7; F = 8.68 and 9.47 respectively) and Minolta color measurements L* (SSC4 and SSC7; F =16.42 and 7.17 respectively), and a* (SSC4 and SSC8; F = 8.05 and 7.36 respectively). No QTL were observed for the color measurements b*, H*, and C*. Alternative models fitting epistasis between QTL were also tested, but detected epistatic interactions were not significant at a genome-wise level. In this work we identify genomic regions related with meat quality traits. Improvement by traditional selection methods is complicated, and finer mapping would be required for their application in introgression programs.     

Effect of long-term selection for increased leanness on meat and eating quality traits in Duroc swine

A study was conducted to evaluate differences in meat and eating quality traits between purebred Duroc pigs sired by boars currently available and pigs sired by boars from the mid 1980s. Two lines were developed by randomly allocating littermate and half-sib pairs of females to matings by current time period (CTP) or old time period (OTP) boars. Matings by CTP boars were made using fresh semen, and matings by OTP boars were via frozen semen. All available barrows and randomly selected gilts were sent to a commercial abattoir and used for meat and eating quality evaluation. A total of 178 pigs from 23 CTP sires and 99 pigs from 15 OTP sires, across 2 replications and at a mean live weight of 109 kg, were slaughtered and analyzed. Chemical intramuscular fat percentage was determined by lab analysis of a slice from the LM at the 10th rib. Additional meat and eating quality traits measured on the LM were Minolta reflectance and Hunter L color (24 h); pH (24 h and 7 d); water-holding capacity; subjective visual scores for color, marbling, and firmness (48 h); Instron tenderness; cooking loss; and trained sensory panel evaluations (7 d). Time period differences were assessed by use of a mixed model that included fixed effects of sire time period, replication, sex, contemporary group, and the interaction of sex x time period. The random effect of dam and the random effect of sire nested within time period were also included. Loins from pigs sired by OTP boars had greater intramuscular fat (3.48 vs. 3.09%) and visual marbling scores (3.54 vs. 3.07), required less Instron force (5.31 vs. 5.98 kg) to compress, and had darker visual color scores (4.09 vs. 3.87) compared with loins from pigs sired by CTP boars (P < 0.05). No differences were observed between time periods for Minolta reflectance, Hunter L (24 h), water-holding capacity, pH (24 h and 7 d), or subjective firmness scores. Trained sensory evaluations revealed more pork flavor and less off-flavor (P < 0.05) for OTP-sired pigs; however, no differences in tenderness score, juiciness score, chewiness score, or cooking loss were found between lines. Long-term selection response in carcass composition has been at the expense of meat and eating quality traits.     

不同屠宰体重商品猪胴体性能、肉品质及相关关系研究

测定了体重70～140 kg阶段120头商品猪的胴体品质和肉质特性,分析了商品猪胴体性能、肉质性状随体重的变化规律及相关程度,为确定适宜上市屠宰体重提供依据。结果表明:70～100 kg体重阶段,随体重增大,平均背膘厚、眼肌面积、皮脂率、肉色和大理石纹显著升高,后腿比例、瘦肉率、骨骼率、L和b值显著降低。胴体和肉质性状间相关程度有强有弱,相关系数有正有负。相同性状间有较强的正相关,相反性状间有较强的负相关。在70～140 kg阶段,胴体重、胴体直长、胴体斜长、眼肌面积、平均背膘厚、瘦肉率、皮脂率、骨骼率、肉色和L值与体重之间呈显著的回归关系,其他指标与体重间的线性相关不显著。     

Genetic parameter estimates of meat quality traits in Duroc pigs selected for average daily gain, longissimus muscle area, backfat thickness, and intramuscular fat content

Using a multitrait animal model BLUP, selection was conducted over seven generations for growth rate (ADG), real-time ultrasound LM area (LMA), backfat thickness (BF), and intramuscular fat content (IMF) to develop a new line of purebred Duroc pigs with enhanced meat production and meat quality. This selection experiment examined 543 slaughtered pigs (394 barrows and 153 gilts) from the first to the seventh generation for meat quality traits. Further, electric impedance and collagen content of loin meat were measured from the fourth to sixth generation. The present study was intended to estimate genetic parameters of the correlated traits of tenderness (TEND), meat color (pork color standard: PCS; lightness = L*), drip loss (DL), cooking loss (CL), pH (PH), electric impedance (IMP), and collagen (COL) of the LM, and the genetic trends of these traits. Respective heritability estimates for IMF, TEND, DL, CL, PCS, L*, PH, IMP, and COL were 0.39, 0.45, 0.14, 0.09, 0.18, 0.16, 0.07, 0.22, and 0.23. Genetic correlations of IMF with ADG and BF were low and positive, but low and negative with LMA. Tenderness was correlated negatively with ADG (-0.44) and BF (-0.59), but positively correlated with LMA (0.32). The genetic correlation between LMA and DL was positive and high (0.64). The genetic correlations of TEND with IMF and COL were low (-0.09 and 0.26, respectively), but a moderate genetic correlation (0.43) between COL and IMF was estimated, suggesting related increases of IMF and connective tissue. Genetic correlations among meat quality traits suggested that when IMF increases, the water holding capacity improves. Genetic trends of meat quality traits showed increased IMF and lighter meat color.     

品种和营养水平对猪生长性能、胴体性状和肉质的影响

本试验旨在研究品种和营养水平对猪生长性能、胴体性状和肉质的影响。选择12对初始体重为(61.16±4.13)kg的高坡猪和"杜×长×太"三元杂交猪(DLT),随机分成4个处理,饲喂不同营养水平[NRC(2012)、中国猪饲养标准(2004)]的全价饲粮,试验猪平均体重达90 kg时屠宰。结果表明:DLT的眼肌面积显著高于高坡猪(P0.05),而肌内脂肪含量、平均背膘厚、肉色的亮度(L*)24 h和黄度(b*)24 h显著低于高坡猪(P0.05);饲喂高营养水平的饲粮可以显著降低猪的料重比(P0.05);饲粮营养水平升高显著提高了高坡猪的平均日增重、平均日采食量、胴体长和肉色的红度(a*)24 h(P0.05),显著降低了肉色的L*24 h、滴水损失以及背最长肌固醇调节元件结合蛋白-1c和激素敏感性脂肪酶mRNA的相对表达量(P0.05);饲粮营养水平升高显著降低了DLT肉色的a*45 m in和a*24 h(P0.05)。综上所述,在本试验条件下,品种和营养水平对猪生长性能、胴体性状和肉质有显著影响;DLT胴体性状优于高坡猪,肉质反之。饲粮营养水平升高显著提高了DLT胴体性状和高坡猪的肉质,对生长性能有一定的改善。     

Mapping QTL for fat area ratios and serum leptin concentrations in a Duroc purebred population

The reduction of extra subcutaneous, intermuscular and abdominal fat is important to increase the carcass lean percentage of pigs. Image analyses of fat area ratios were effective for estimation of separated fat in pig carcasses. Serum concentrations of leptin are useful as physiological predictors of fat accumulation in pigs. The objectives of the present study were to perform a quantitative trait locus (QTL) analysis for fat area ratios and serum leptin concentrations in a Duroc purebred population. Pigs (n = 226 to 538) were measured for fat area ratios of carcass cross‐sections at the fifth to sixth thoracic vertebrae, half body length and last thoracic vertebra using an image analysis system, and serum leptin concentration. In total, animals were genotyped for 129 markers and used for QTL analysis. For fat area ratios, four significant and 12 suggestive QTLs were detected on chromosomes 1, 6, 7, 8, 9, 12 and 13. Significant QTLs were detected on the same region of chromosome 6, which was located near a leptin receptor gene. For serum leptin concentrations, two significant and two suggestive QTLs were detected on chromosomes 6, 9, and 16, and the QTLs on chromosome 6 were also in the same region for fat area ratios.     

The effect of adipocyte and heart fatty acid-binding protein genes on intramuscular fat and backfat content in Meishan crossbred pigs

Effects of genetic variation in porcine adipocyte and heart fatty acid-binding protein genes, A-FABP and H-FABP, respectively, on intramuscular fat (IMF) content and backfat thickness (BFT) were examined in F2 crossbreds of Meishan and Western pigs. The involvement of each FABP gene in IMF accretion was studied to confirm previous results for Duroc pigs. The F2 crossbred pigs were genotyped for various markers including microsatellite sequences situated within both FABP genes. Linkage analysis assigned the A-FABP and H-FABP genes to marker intervals S0001-S0217 (20 cM) on SSC4 and Sw316-S0003 (16.6 cM) on SSC6, respectively, refining previous chromosomal assignments. Next, the role of both chromosome regions/genes on genetic variation in IMF content and BFT was studied by 1) screening SSC4 and SSC6 for QTL affecting both traits by performing a line-cross analysis and 2) estimation of the effect of individual A-FABP and H-FABP alleles on both traits. In the first analysis, suggestive and chromosome-wise significant evidence for a QTL affecting IMF was detected on SSC6. The H-FABP gene is a candidate gene for this effect because it resides within the large region containing this putative QTL. The second analysis showed a considerable but nonsignificant effect of H-FABP microsatellite alleles on IMF content. Suggestive evidence for a QTL affecting BFT was found on SSC6, but H-FABP was excluded as a candidate gene. In conclusion, present and previous results support involvement of H-FABP gene polymorphisms in IMF accretion independently from BFT in pigs. Therefore, implementation of these polymorphisms in marker-assisted selection to control IMF content independently from BFT may be considered. In contrast to previous findings for Duroc pigs, no evidence was found for an effect of the A-FABP gene on IMF or BFT in this population.     

A genome scan for quantitative trait loci affecting the length of small intestine in a White Duroc × Chinese Erhualian intercross resource population

The small intestine is a vital organ in animal gastrointestinal system, in which a large variety of nutrients are absorbed. To identify quantitative trait loci (QTL) for the length of porcine small intestine, phenotypic values were measured in 1034 individuals at 240 d from a White Duroc × Chinese Erhualian intercross F₂ population. The length of small intestine showed strong correlation with growth traits and carcass length in the F2 population. A whole‐genome scan was performed based on 183 microsatellites covering the pig genome in the F₂ population. A total of 10 QTL for this trait were identified on 8 pig chromosomes (SSC), including four 1% genome‐wide significant QTL on SSC2, 4, 7 and 8, one 5% genome‐wide significant QTL on SSC12, and five 5% chromosome‐wide significant QTL on SSC5, 7, 13 and 14. The Erhualian alleles were generally associated with shorter length of the small intestine except the alleles on SSC7 and 13. The QTL on SSC4 overlapped with the previously reported QTL for the length of small intestine. Several significant QTL on SSC2, 8, and 12 were consistent with previous reports. The significant QTL detected on SSC7 was reported for the first time. All QTL identified in this study corresponded to the known region significantly associated with growth traits, supporting the important role of the length of small intestine in pig growth.