Evaluation of effects of multiple candidate genes (LEP,LEPR, MC4R,PIK3C3, and VRTN) on production traits in Duroc pigs

We evaluated multiple effects of genetic variations of five candidate loci (LEP, LEPR, MC4R, PIK3C3 and VRTN) on four production traits (average daily weight gain (ADG); backfat thickness (BFT); loin eye muscle area (EMA); and intramuscular fat content (IMF)) in a closed nucleus herd of pure Duroc pigs. Polymorphisms in LEPR, MC4R and PIK3C3 had significant single gene effects on ADG and BFT. The additive genetic variance in ADG and BFT (16.99% and 22.51%, respectively) was explained by genetic effects of these three loci. No correlations were observed between the LEP genotype and production traits in this study. Although we detected marginally epistatic interactions between LEPR and PIK3C3 on the eye muscle area, there were no significant epistatic effects on any traits among all loci pairs. These results suggest that LEPR, MC4R, PIK3C3 and VRTN may independently influence growth rate and fat deposition. Furthermore, the statistical models for predicting the breeding values of each trait had the lowest Akaike's information criterion values when considering the effect of the MC4R, LEPR, PIK3C3 and VRTN genotype simultaneously. These results suggest that LEPR, MC4R, PIK3C3 and VRTN are useful markers for accurately predicting breeding values in Duroc pigs.     

An insertion/deletion variant of a thymine base in exon 2 of the porcine beta 3‐adrenergic receptor gene associated with loin eye muscle area

An insertion/deletion variant of a thymine base (T5 and T6) in exon 2 of porcine beta 3‐adrenergic receptor (ADRB3) gene has been described. In the current study, we made an association study between the ADRB3 polymorphisms and production traits in 735 Duroc pigs. The allele frequencies for the T5 and T6 alleles in our study population were 0.433 and 0.567, respectively. Any associations between ADRB3 genotype and average daily weight gain during test period, or backfat thickness and intramuscular fat content were not detected in either sex. However the size of the loin eye muscle area (EMA) was significantly associated with ADRB3 genotypes in gilts. T6‐homozygous gilts had a higher mean of EMA (40.6 ± 0.6 cm²) than T5‐homozygous (38.1 ± 0.4 cm², P = 0.002) and heterozygous (38.8 ± 0.3 cm², P = 0.034) gilts. This association was not detected in males. In addition, a multiple traits animal model best linear unbiased predictor (BLUP) analysis revealed that the T6‐homozygous genotype had positive effects on breeding value of EMA. Accordingly, we suggest that ADRB3 polymorphism has the potential to be an important genetic marker for prediction of EMA in Duroc pigs.     

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.     

Effects of porcine leptin receptor gene polymorphisms on backfat thickness,fat area ratios by image analysis,and serum leptin concentrations in a Duroc purebred population

The leptin receptor (LEPR) gene is considered a candidate gene for fatness traits. It is located on SSC 6 in a region in which quantitative trait loci (QTLs) for backfat thickness (BF), fat area ratios, and serum leptin concentration (LEPC) have previously been detected in a Duroc purebred population. The objectives of the present study were to identify porcine LEPR polymorphisms and examine the effects of LEPR polymorphisms on fatness traits in this same population. The Duroc pigs (226 to 953 pigs) were evaluated for BF, fat area ratios using image analysis, and LEPC. A total of seven single nucleotide polymorphisms (SNPs) in the full‐length LEPR coding region were identified in pigs from the base population. Four non‐synonymous SNPs of the LEPR gene and 15 microsatellite markers on SSC 6 were then genotyped in all pigs. During candidate gene analysis, we detected significant effects of the non‐synonymous SNP c.2002C>T in exon 14 on all traits. In fine mapping analysis, significant QTLs for BF, fat area ratios, and LEPC were detected near the LEPR gene in the same region. These results indicated that the c.2002C>T SNP of LEPR has a strong effect on BF, fat area ratios and LEPC.     

Genetic correlations among fatty acid compositions in different sites of fat tissues, meat production, and meat quality traits in Duroc pigs

This study estimated genetic parameters for fatty acids of different sites of fat tissue, meat production, and meat quality traits of Duroc pigs selected during 7 generations for ADG, LM area, backfat thickness (BF), and intramuscular fat (IMF). For this study, 394 barrows and 153 gilts were slaughtered at 105 kg of BW. High heritabilities for C18:0 of outer and inner subcutaneous fat tissue were estimated, respectively, as 0.54 and 0.51; those of intermuscular and intramuscular fat were 0.40 and 0.51, respectively. Genetic and phenotypic correlations of ADG and BF with saturated fatty acids of outer and inner subcutaneous fat were positive, but those with C16:1 and C18:2 were negative, and those with C18:1 were nearly zero. Genetic and phenotypic correlations between LM area and respective fatty acids showed opposite results. Respective genetic and phenotypic correlations of melting points with C18:0 and C18:1 were positive and high, and negative and high, respectively. Genetic correlations between cooking loss and SFA (C14:0, C16:0, and C18:0) of IMF were positive and moderate: 0.56, 0.47, and 0.47, respectively. On the other hand, monosaturated fatty acid of C18:1 was highly and negatively correlated with cooking loss (-0.61). Moreover, high genetic correlation between meat color (pork color standard and lightness) and fatty acid compositions of IMF suggest that the SFA (C14:0, C16:0, and C18:0) were correlated genetically with meat lightness and that unsaturated fatty acid compositions (C18:1 and C18:2) were correlated with meat darkness. Results of this study suggest that the fatty acid composition of adipose tissue is correlated genetically with meat production and meat quality traits.     

Genetic parameters for feed efficiency traits and their relationships with growth and carcass traits in Duroc pigs

Genetic parameters for feed efficiency traits of 380 boars and growth and carcass traits of 1642 pigs (380 boars, 868 gilts and 394 barrows) in seven generations of Duroc population were estimated. Feed efficiency traits included the feed conversion ratio (FCR), and nutritional (RFI(nut)), phenotypic (RFI(phe)) and genetic (RFI(gen)) residual feed intake. Growth and carcass traits were the age to reach 105-kg body weight (A105), loin eye muscle area (EMA), backfat (BF), intra-muscular fat (IMF) and meat tenderness. The mean values for RFI(phe) and RFI(gen) were close to zero and for RFI(nut) was negative. All the measures of feed efficiency were moderately heritable (h(2) = 0.31, 0.38, 0.40 and 0.27 for RFI(nut), RFI(phe), RFI(gen) and FCR respectively). The heritabilities for all growth and carcass traits were moderate (ranged from 0.37 to 0.45), except for BF, which was high (0.72). The genetic correlations of RFI(phe) and RFI(gen) with A105 were positive and high. Measures of RFI were correlated negatively with EMA. BF was more strongly correlated with measures of RFI (r(g) > or = 0.73) than with FCR (r(g) = 0.52). Selection for daily gain, EMA, BF and IMF caused favourable genetic changes in feed efficiency traits. Results of this study indicate that selection against either RFI(phe) or RFI(gen) would give a similar correlated response in carcass traits.     

Association of swine vertnin (VRTN) gene with production traits in Duroc pigs improved using a closed nucleus breeding system

Vertnin (VRTN) is involved in the variation of vertebral number in pigs and it is located on Sus scrofa chromosome 7. Vertebral number is related to body size in pigs, and many reports have suggested presence of an association between body length (BL) and meat production traits. Therefore, we analyzed the relationship between the VRTN genotype and the production and body composition traits in purebred Duroc pigs. Intramuscular fat content (IMF) in the Longissimus muscle was significantly associated with the VRTN genotype. The mean IMF of individuals with the wild‐type genotype (Wt/Wt) (5.22%) was greater than that of individuals with the Wt/Q (4.99%) and Q/Q genotypes (4.79%). In addition, a best linear unbiased predictor of multiple traits animal model showed that the Wt allele had a positive effect on the IMF breeding value. No associations were observed between the VRTN genotype and other production traits. The VRTN genotype was related to BL. The Q/Q genotype individuals (100.0 cm) were longer than individuals with the Wt/Q (99.5 cm) and Wt/Wt genotypes (98.9 cm). These results suggest that in addition to the maintenance of an appropriate backfat thickness value, VRTN has the potential to act as a genetic marker of IMF.     

Genetic analyses of growth, real-time ultrasound, carcass, and pork quality traits in Duroc and Landrace pigs: II. Heritabilities and correlations.

Knowledge of the genetic control of pork quality traits and relationships among pork quality, growth, and carcass characteristics is required for American swine populations. Data from a 2 x 2 diallel mating system involving Landrace and Duroc pigs were used to estimate heritabilities and genetic correlations among growth (ADG), real-time ultrasonic (US) measures of backfat thickness (BF) and longissimus muscle area (LMA), carcass characteristics, and various pork quality traits. Data were collected from 5,649 pigs, 960 carcasses, and 792 loin chops representing 65, 49, and 49 sires, respectively. Genetic parameters were estimated by REML assuming animal models. Heritability estimates were moderate to high for ADG, USBF, USLMA, carcass BF, and LMA, percentage of LM lipid (IMF), pork tenderness, and overall acceptability. Estimates were low to moderate for percentage of cooking loss, pH, shear force, percentage of LM water, water-holding capacity (WHC), pork flavor, and juiciness. Genetic correlations between US and carcass measures of BF and LMA indicate that selection based on US data will result in effective improvement in carcass characteristics. Selection for increased LMA and(or) decreased BF using US is, however, expected to result in decreased IMF and WHC, increased percentage of LM water and shear value, and in decreased juiciness, tenderness, and pork flavor. Average daily gain was favorably correlated with IMF and unfavorably correlated with shear force. Selection for increased ADG is expected to improve WHC but to decrease the percentage of LM water, with an associated decrease in juiciness. The results of this study suggest the feasibility of including meat quality in selection objectives to improve product quality. Favorable genetic correlations between IMF and eating quality traits suggest the possible merit of including IMF in the selection objective to improve, or restrict change in, pork eating quality.     

中国西门塔尔牛血管生成素样蛋白3基因多态性及其与肉质性状的关联性分析

本研究旨在分析血管生成素样蛋白3(angiopoietin-like protein 3,ANGPTL3)基因的单核苷酸多态性(SNPs)及其与中国西门塔尔牛肉质性状的关联性,寻找可用于辅助选择的分子标记。随机选取饲养条件相同的98头中国西门塔尔牛为研究对象,采用PCR-SSCP技术结合DNA测序技术检测ANGPTL3基因的SNP。运用SPSS 19.0软件对ANGPTL3基因的不同基因型与肉质性状进行关联性分析。经测序发现,ANGPTL3基因外显子4中存在1个突变位点G7358C,存在2种基因型:CD、DD。关联性分析结果表明,G7358C突变位点的不同基因型与胴体脂肪覆盖率、眼肌面积、肌内脂肪和大理石花纹差异显著相关(P0.05),CC基因型个体胴体脂肪覆盖率、眼肌面积、肌内脂肪和大理石花纹显著高于CD基因型个体(P0.05)。试验结果表明,G7358C位点的CC基因型为优势基因型,与胴体脂肪覆盖率、眼肌面积、肌内脂肪和大理石花纹等肉用性状有相关性,ANGPTL3基因有望作为分子标记辅助选择的候选基因。     

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.     

Genetic analyses of growth, real-time ultrasound, carcass, and pork quality traits in Duroc and Landrace pigs: I. Breed effects.

Knowledge of breed effects on carcass and pork quality traits is required to develop commercial crossbreeding programs that emphasize product quality. A 2 x 2 diallel mating system involving Landrace and Duroc pigs was used to estimate individual heterosis, direct breed effects and reciprocal cross differences for post-weaning growth, real-time ultrasound, carcass, and pork quality traits. Data from 5,649 pigs and 960 carcasses representing 65 and 49 sires, respectively, were analyzed assuming animal models. Duroc-sired pigs had 2.1 cm shorter carcasses with 7.3 mm less 10th rib backfat (BF), 4.4 cm2 larger longissimus muscle area (LMA), yielded 2.1 kg more estimated fat standardized lean (FSL), gained 16.5 g more estimated lean per day of age (LDOA), and had 1.0% less water (PWAT) and 1.9% more intramuscular fat (IMF) in the longissimus muscle than did Landrace-sired pigs (P less than .01), adjusted to an off-farm live weight of 111 kg. Reciprocal cross differences were detected for BF, LMA, FSL, LDOA and for subjective marbling, firmness, and muscling scores (P less than .01). Durocsired F1 barrows had 6.3 mm less BF and 5.9 cm2 larger LMA, yielded 3.2 kg more FSL, gained 22.3 g more LDOA, and had less marbling in the longissimus muscle and heavier ham muscling than reciprocal cross barrows. Heterosis estimates (P less than .05) were 27.6 g/d (3.2%) for ADG, -5.8 d (-3.6%) for off-test age, 2.7 cm (3.4%) for carcass length, 1.5 kg (7.2%) for FSL, 14.7 g (5.7%) for LDOA, -.07 (-3.6%) for muscle color, -.5% (-13.2%) for IMF, and .3% (.3%) for PWAT. Breed effects were not detected (P greater than .10) for muscle pH, cooking loss, shear value, and water-holding capacity or for eating quality traits. Reciprocal cross differences suggest an advantage in using the Duroc as a terminal sire, but improved carcass composition and higher intramuscular fat did not seem to affect eating quality traits.     

Nucleotide sequence polymorphisms of beta1‐, beta2‐, and beta3‐adrenergic receptor genes on Jinhua,Meishan, Duroc and Landrace pigs

The full amino acid coding sequences of adrenergic receptor genes beta1, beta2, and beta3 (ADRB1, ADRB2, and ADRB3)were determined for Jinhua, Meishan, Duroc and Landrace pigs. Non‐synonymous substitution of Arg458Pro was found in the porcine ADRB1 gene, resulting in a 469 amino acid sequence. Continuous substitutions of Asn29Asp and Glu30Gln were found in the porcine ADRB2 gene, resulting in a 418 amino acid sequence. Additionally, a Lys30 polymorphism of the ADRB2 gene was found in the Jinhua pigs. There were three non‐synonymous substitutions of Asn24Thr, Arg264Gln and Asn398Asp on the porcine ADRB3 gene. A thymine insertion in the ADRB3 gene, resulting in a protein with two fewer amino acids, was found in the Jinhua and Meishan pigs. To assess the effect of ADRB polymorphisms on porcine subcutaneous fat layer thickness, we calculated the genetic frequency of the variants in fatty and lean groups, each consisting of 24 pigs that were crossbreds of Duroc and Jinhua pigs. The effect of the ADRB3 gene polymorphism was not evaluated, because there was insufficient variation on the ADRB3 gene in the examined groups. Although Fisher's exact test showed no significant difference in the frequency of ADRB1 and ADBR2 variants between the two groups, the Arg458 variant of ADRB1 was higher (P = 0.11) in the lean group, and pigs in that group had a thinner fat layer than did those with the Pro458 variant. These results imply a possibility of ADRB1 polymorphism as a minor factor in porcine fat layer thickness. The Asp29 variant of ADRB2 was higher in the lean group (P = 0.11), and the Glu30 variant was higher in the fatty group (P = 0.15), but the Asp29 variant was found only in the Chinese pigs. Thus, the effect of ADRB2 polymorphisms was not clear in this study.     

Deposition rates and accretion patterns of intramuscular fat, loin muscle area, and backfat of Duroc pigs sired by boars from two time periods

A study was conducted to evaluate differences in performance and in carcass composition and tissue deposition rates between purebred Duroc pigs sired by boars currently available and those 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. Pigs from 2 replications were placed on test at a group mean BW of 63.5 kg. Serial ultrasonic measurements of the 10th-rib LM area (LMA), off-midline backfat (BF10), and intramuscular fat percentage (IMF) were collected every 2 wk in the first replication and used to assess deposition rate differences. Off-test ultrasonic LMA, BF10, and IMF measurements from a total of 557 pigs from 23 CTP sires and 232 pigs from 15 OTP sires across 2 replications and at a mean BW of 109 kg were evaluated. All available barrows and randomly selected gilts (n = 277) were sent to a commercial abattoir, and carcass measurements of 10th-rib backfat, last-rib backfat, last lumbar backfat, and LMA were collected. Analysis of serial backfat measurements revealed a linear relationship between back-fat and BW between 73 and 118 kg for pigs from both time periods. Pigs sired by OTP boars deposited more backfat (P < 0.05) at a faster rate than pigs sired by CTP boars over the entire test period. A curvilinear cumulative tissue deposition pattern was revealed for ultrasonically estimated LMA and IMF within both time periods. Significant linear and quadratic regression coefficient differences between lines indicated that pigs sired by CTP boars deposited more LMA and less IMF per kilogram of BW gain than pigs sired by OTP boars. Pigs sired by CTP boars had more LMA and less BF10 (P < 0.05), whereas pigs sired by OTP boars had more IMF (P = 0.04). Carcass evaluation revealed more (P < 0.01) carcass measurements of LMA and less (P < 0.05) carcass measurements of 10th-rib backfat, carcass measurements of last-rib backfat, and carcass measurements of last lumbar backfat for pigs sired by CTP boars. No difference (P > 0.05) between the time periods was found for ADG over the entire test period. Results from this study illustrate that significant progress in carcass composition has been realized within the Duroc breed since the mid-1980s. The long-term selection response in carcass leanness has also resulted in changes in deposition rates of correlated traits such as LMA and IMF.     

Allelic frequencies of PRKAG3 in several pig breeds and its technological consequences on a Duroc × Landrace‐Large White cross

The allelic frequencies of PRKAG3 gene (the RN gene) have been investigated in several pig breeds. R200Q mutation appear only in Hampshire pigs, whereas V199I mutation is most abundant in Iberian, Porco Celta or Bizaro, and less in breeds selected for muscularity as Duroc, Landrace and Pietrain. A thorough study of phenotypic effects of V1991 has been performed in a Duroc × Landrace‐Large White cross. 199I homozygous pigs show increased pH₂₄ values in ham homogenates and loin (0.14 and 0.16 pH units, respectively) compared to 199V homozygous ones. Meat of 199I homozygous pigs exudates 42.6% less fluid and is darker (2.46 ‘L’‐value units). 199I homozygous pigs are fatter (4.2 mm more backfat thickness) and contain less muscle mass in ham (1.0 percentage points) and shoulder (2.7 percentage points), than 199V homozygous ones. 199I homozygous pigs contain 7.3% less protein in the belly and 8.5% more fat in shoulder muscle mass than 199V homozygous pigs. 199I homozygous pigs have also superior functional properties: better gelling (22.8% larger G′ value) and emulsion capacities (14 percentage points less of total exuded fluid), and higher curing yield in the belly (6 percentage points more). These data support the adipogenic character of the V199I mutation. The advantages and disadvantages of selecting any of the two PRKAG3 alleles for position 199 are discussed.     

杜洛克猪HLCS基因多态位点与生长发育性状的相关性分析

本研究旨在明确羧化全酶合成酶（holocarboxylase synthetase,HLCS）基因突变与杜洛克猪生长发育性状的相关性。利用Illumina SNP60芯片测序结果研究HLCS基因的突变位点,分析突变位点的多态性信息、突变位点与生长发育性状的关联性及突变位点的单倍型。结果显示,杜洛克猪HLCS基因具有4个SNPs位点：Ssc13：200455646 T>C、Ssc13：200458655 G>C、Ssc13：200504530 G>T、Ssc13：200551864 T>G,均符合Hardy-Weinberg平衡状态（P>0.05）,呈现中度多态性。关联分析结果发现,Ssc13：200455646 T>C位点TT基因型100 kg背膘、剩余采食量均显著高于TC和CC基因型（P<0.05）;Ssc13：200458655 G>C位点GG基因型个体100 kg背膘、剩余采食量均显著高于CG和CC基因型（P<0.05）;Ssc13：200504530 G>T位点GT基因型平均日采食量、平均日增重均显著高于TT基因型（P<0.05）,GT基因型个体100 kg日龄显著小于TT基因型（P<0.05）;Ssc13：200551864 T>G位点TG基因型平均日采食量、平均日增重均显著高于GG基因型（P<0.05）,TG基因型个体100 kg日龄显著小于GG基因型（P<0.05）;其余性状各位点不同基因型间无显著差异（P>0.05）。Ssc13：200455646 T>C和Ssc13：200458655 G>C位点呈现高度连锁,Ssc13：200504530 G>T与Ssc13：200551864 T>G位点呈现高度连锁。结果表明,HLCS基因4个SNPs位点的多态性与杜洛克猪的剩余采食量、平均日采食量、平均日增重、100 kg日龄和100 kg背膘均具有显著相关性,可为猪的生长发育遗传改良奠定基础。     

Association between melanocortin 4 receptor (MC4R) gene haplotypes and carcass and production traits in Italian Large White pigs evaluated with a selective genotyping approach

Melanocortin 4 receptor (MC4R) plays a key role in controlling energy homeostasis. Several studies have already reported effects on production traits of polymorphisms identified in the porcine MC4R gene. In this study we analysed data on 6 MC4R polymorphisms (c.-780C>G; c.-135C>T; c.175C>T; c.707G>A or p.Arg236His; and c.892G>A or p.Asp298Asn; c.?430A>T) genotyped from (1) two groups of Italian Large White pigs (280+280 animals) with extreme estimated breeding values (EBVs) for back fat thickness (BFT), selected among a performance tested population of about 12,000 pigs, and from (2) 19 Italian Duroc pigs. Two haplotypes, differentiated by the c.892G>A, were identified in the Duroc populations. Four haplotypes were identified in the Italian Large White population, one of which (haplotype 4) was identified for the first time in this study. Single marker and haplotype association analyses for BFT were obtained by comparing allele and haplotype frequency differences from the two extreme tails using χ² and Cochran–Armitage trend tests. Results confirmed the effects of the c.892G>A single nucleotide polymorphism (SNP) on BFT, as also defined by different distributions in the two tails of haplotypes carrying the alternative nucleotides at this polymorphic site (P<0.01). In addition different distributions of haplotype 4 in the two extreme groups suggested that it might affect the same trait (P<0.10). Association analyses for several other traits (average daily gain, ADG; feed gain ratio, FGR; weight of lean cuts; ham weight) were carried out by using EBVs and Random Residuals: significant effects (P<0.05) were only found for the p.Asp298Asn mutation on ADG and FGR. Results did not support any relevant effect of the p.Arg236His mutation on any trait. Data reported in this study contribute to better understand the role of MC4R variants in affecting production traits in pigs, a prerequisite to consider polymorphisms in this gene for marker assisted selection.     

Maternal effects on traits measured during postweaning performance test of swine from four breeds

The objective of this study was to investigate the importance of maternal genetic effects on postweaning performance traits of Yorkshire, Landrace, Duroc, and Hampshire breeds of swine. Data consisted of performance test records collected in a commercial swine operation from 1992 to 1999. Boars from 60% of the litters were culled at weaning based on a combination of maternal and performance indexes that differed by breed. Remaining boars and all females were grown to 100 d of age. At this time all pigs were weighed (WT100) and selected for testing using recalculated breed-specific indexes (n = 15,594, 55,497, 12,267, and 9,782 for Landrace, Yorkshire, Duroc, and Hampshire, respectively). All pigs were weighed at the end of the 77-d test, and backfat (BF) and loin eye area (LEA) were measured over the 12th rib by ultrasound. Average daily feed intake was calculated for boars, and ADG was calculated for all animals. Genetic parameters were estimated for each breed and trait using multiple-trait DFREML procedures. Fixed effects were contemporary groups and either initial or final test age as a covariate. Four models were examined. Model 1 included only the additive genetic effect of the animal. Model 2 added the common litter environmental effect; Model 3 added the maternal genetic value assumed to be uncorrelated with additive genetic effects. Model 4 was the same as Model 3 with additive and maternal genetic effects assumed to be correlated. All models were two-trait models with WT100 as the second trait. Ratios of likelihoods were used to compare models. Maternal effects were important (P < 0.05) for WT100, ADG, ADFI, LEA, and BF in Landrace; for WT100, ADG, LEA, and BF in Yorkshire; for WT100 and ADG in Duroc, and for WT100 in Hampshire. Estimates of heritabilities for direct additive effects using the appropriate model for ADG, ADFI, LEA, and BF were 0.28, 0.34, 0.48, and 0.63 for Landrace; 0.26, 0.31, 0.39, and 0.65 for Yorkshire; 0.14, 0.20, 0.26, and 0.35 for Duroc; and 0.17, 0.23, 0.25, and 0.31 for Hampshire, respectively. Heritability estimates for maternal genetic effects for ADG, ADFI, LEA, and BF were 0.02, 0.05, 0.06, and 0.07 for Landrace and 0.02, 0, 0.04, and 0.06 for Yorkshire, respectively. They were zero for all traits except ADG (0.03) in Duroc and for all traits in Hampshire. Maternal effects may need to be considered in genetic evaluation of performance traits in some breeds of swine.