Core and variable antimicrobial resistance genes in the gut microbiomes of Chinese and European pigs

Monitoring the prevalence of antimicrobial resistance genes(ARGs)is vital for addressing the global crisis of antibiotic-resistant bacterial infections.Despite its importance,the characterization of ARGs and microbiome structures,as well as the identification of indicators for routine ARG monitoring in pig farms,are still lacking,particularly concerning variations in antimicrobial exposure in different countries or regions.Here,metagenomics and random forest machine learning were used to elucidate the ARG profiles,microbiome structures,and ARG contamination indicators in pig manure under different antimicrobial pressures between China and Europe.Results showed that Chinese pigs exposed to high-level antimicrobials exhibited higher total and plasmid-mediated ARG abundances compared to those in European pigs(P<0.05).ANT(6)-Ib,APH(3')-IIIa,and tet(40)were identified as shared core ARGs between the two pig populations.Furthermore,the core ARGs identified in pig populations were correlated with those found in human populations within the same geographical regions.Lactobacillus and Prevotella were identified as the dominant genera in the core microbiomes of Chinese and European pigs,respectively.Forty ARG markers and 43 biomarkers were able to differentiate between the Chinese and European pig manure samples with accuracies of 100%and 98.7%,respectively.Indicators for assessing ARG contamination in Chinese and European pigs also achieved high accuracy(r=0.72-0.88).Escherichia flexneri in both Chinese and European pig populations carried between 21 and 37 ARGs.The results of this study emphasize the importance of global collaboration in reducing antimicrobial resistance risk and provide validated indicators for evaluating the risk of ARG contamination in pig farms.

Genetic Screening of Halothane Gene on Selected Philippine Native Pig Herds

The establishment of nucleus herds (NHs) of Native Pigs (NPs) at various R&D stations in the Philippines is currently being undertaken for food security and genetic conservation advocacy. Marker-assisted selection (MAS) is being utilized to identify individuals carrying favorable alleles of genes associated with production traits and screen out genetic defects (GD) for breeding purposes. Porcine Stress Syndrome (PSS) caused by a mutation in Halothane (HAL) gene is a GD frequently found in commercial breeds that when expressed, causes pale, soft, exudative (PSE) meat. PSE is inferior quality meat undesirable in the market causing economic losses to the swine industry. Thus, this study was conducted to screen the HAL gene through mutagenically separated-polymerase chain reaction (MSPCR) in selected NP herds and assessed its repeatability in local breeds. Results showed that out of 577 screened individuals, 543 (94.11%) were normal (NN), 0 (0%) were homozygous mutant (nn) and 34 (5.89%) were heterozygous carriers (Nn). Therefore, the optimized PSS screening protocol using MSPCR is also applicable to local breeds. As such, the availability of genetic tests for PSS could be useful in improving the Philippine NPs breeding selection and inhibiting or eliminating PSS mutant incidence within its nucleus herd.

Localization of An Exogenous GH Gene on Chromosomes of Transgenic Pig by in situ Hybridizaiton

近些年来随着原位杂交技术的不断改进，该技术已广泛用于染色体的基因定位。非放射性标记探针的应用使基因定位变得更加简单易行，从而有可能对动物的转基因进行定位研究。本文首次采用胶体金标记药盒（Ａｎｔｉｄｉｇｏｘｉｇｅｎｉｎｇｏｌｄ）和银加强试剂（Ｓｉｌｖｅｒｅｎｈａｎｃｅｍｅｎｔｒｅａｇｅｎｔｓ）的非同位素原位杂交技术对转基因猪外源基因进行了定位研究。如Ｆｉｇ．１所示：表达质粒ｐＳＭＴＰＧＨ含有载体ｐＵＣ１９，羊启动子ＭＴ０１１和猪生长激素ＰＧＨ基因。选５头带有ｐＳＭＴＰＧＨ的转基因猪，分别制备含有染色体ＤＮＡ的杂交膜。用ＢｇｌＩＩ和ＳｍａＩ对ｐＳＭＴＰＧＨ进行完全酶切，收集０．９Ｋｂ片段作为探针，以ｄｉｇ１１ｄＵＴＰ进行标记。探针与ＤＮＡ杂交后，用Ａｎｔｉｄｉｇｏｘｉｇｅｎｉｎｇｏｌｄ和Ｓｉｌｖｅｒｅｎｈａｎｃｅｍｅｎｔｒｅａｇｅｎｔｓ进行显色反应。胰酶法Ｇ—显带后，用光学显微镜检查。选择分散相良好、显影银颗粒清楚的玻片进行摄影记录（Ｆｉｇ．２）。对染色体上的显影银颗粒进行统计分析，参照家猪的染色体标准带型，确定外源ＰＧＨ基因整合位点。Ｆｉｇ．３为４１０４号转基因猪染色体上的银颗粒分布情况。对５头?

Association of polymorphisms of Nramp1 gene with immune function and production performance of large white pig

The present research was designed to study the association of polymorphism of natural resistance-associated macrophage proteinl （Nrampl） with some immune function and the production performance in Large White pig. The PCR-RFLP technique was applied to analyze the correlation between the polymorphisms of Nrampl gene and immune function [value of Polymorphonuclear Leukocytes （PMN） obtained by Nitroblue Tetrazolium （NBT） Reduction and effect of Cytotoxin in Monocyte] and production performance in 165 Large White pigs. The results showed that there was one Nde I restriction locus in Large White pig, and both values of PMN by NBT Reduction and effect of Cytotoxin in Monocyte in genotype BB were higher than those in genotype AB （P〈0.05）. Simultaneously, the weight of 180-day-old pigs with genotype BB was higher than that with genotype AB （P〈0.05）. The results indicated that there was a significant correlation between different genotypes of Nrampl gene and Immune function and production performance, and it can be regarded as a candidate gene of disease resistance. All these results provide valuable reference to further studies of pig disease resistance.

Genomic and transcriptomic analyses reveal selection of genes for puberty in Bama Xiang pigs

The Bama Xiang pig （BMX） Chinese indigenous breed is a famous early-maturing with a two-end black coat To uncover the genetic basis of the BMX phenotype, we conducted comparative genomic analyses between BMX and East Asian wild boars and Laiwu pigs, respectively. Genes under positive selection were enriched in pathways associated with gonadal hormone and melanin synthesis, consistent with the phenotypic changes observed during development in BMX pigs. We also performed differentially expressed gene analysis based on RNA-seq data from pituitary tissues of BMX and Large White pigs. The CTTNBP2NL, FRS2, KANK4, and KATNAL1 genes were under selection and exhibited expressional changes in the pituitary tissue, which may affect BMX pig puberty. Our study demonstrated the positive selection of early maturity in the development of BMX pigs and advances our knowledge on the role of regulatory elements in puberty evolution in pigs.

Identification and Detection of Actinobacillus pleuropneumoniae in Infected and Subclinically Infected Pigs by Multiplex PCR Based on the Genes ApxIVA and OmlA

PCRs based on different genes of Actinobacillus pleuropneumoniae have been developed for detecting and identifying A. pleuropneumoniae. Some of them could amplify positive fragments from the phylogenetically closely related species bacteria. To improve veracity and specificity of PCR, a species-specific multiplex PCR assay was developed to identify and detect A. pleuropneumoniae, based on the 3＇-terminus of the species-specific apxlVA gene and the already existing species-specific primers in the omlA gene. Both 346-bp and 950-bp fragments could be simultaneously amplified from all A. pleuropneumoniae reference strains and isolates, and the species specificity of the assay was evaluated with a collection of ten strains representing eight different species bacteria including species normally found in the respiratory tracts of swine. All of these strains turned out negative in the multiplex PCR. All sequences of products of multiplex PCR randomly sampled were also correct. The sensitivity of the multiplex PCR was determined to be 10 pg of A. pleuropneumoniae DNA. The multiplex PCR and bacterial isolation were compared to determine their sensitivities by using experimentally infected pigs and clinical disease pigs. The multiplex PCR was more sensitive than bacterial isolation. The multiplex PCR was also evaluated on mixed bacterial cultures from clinical healthy pigs. 26/100 （26%） of the subclinically infected pigs were detected from clinical healthy pigs. The results indicate that the multiplex PCR assay is a sensitive, highly specific, and effective diagnostic tool for identification and detection of A. pleuropneumoniae.

Adenoviral-mediated Hath1-EGFP gene transfer into guinea pig cochlea through intact round window membrane

Objective To study expression of adenoviral-mediated Hath1-EGFP gene in the guinea pig cochlea after transfer through intact round window membrane(RWM), and to assess its effects on hearing. Methods Twenty adult guinea pigs were used, of which: 12 were surgically inoculated with Ad-Hath1-EGFP in the bony groove of round window niche, and 8 with artificial perilymph. Auditory brainstem response(ABR) thresholds were determined in all animals before and 5 days after surgery. On post-surgery day 5 and day 14, animals were sacrificed and whole mounts of cochlea and frozen sections were examined. Results ABR tests showed no significant change of hearing after the surgery. Strong fluorescence staining in the cochleae was seen in Ad-Hath1-EGFP groups. The highest levels of gene expression were seen in the post-surgery day 5 group with little decrease on post-surgery day 14.The contralateral cochlea and those in the control groups were free of fluorescence staining. Conclusion The transgenic Hath1-EGFP can be effectively delivered into the inner ear through intact RWM, in an atraumatic manner.

Gene expression of vascular endothelial growth factor A and hypoxic adaptation in Tibetan pig

Background： Vascular endothelial growth factor A （VEGFA） can induce endothelial cell proliferation, promote cell migration, and inhibit apoptosis. These processes play key roles in physiological blood vessel formation and pathological angiogenesis. Methods： In this study, we examined VEGFA gene expression in the heart, liver, and kidney of Tibetan pigs （-I-P）, Yorkshire pigs that migrated to high altitudes （YH）, and Yorkshire pigs that lived at low altitudes （YL）. We used PCR and Sanger sequencing to screen for single nucleotide polymorphisms （SNPs） in 5＇-flanking DNA and exons of the VEGFA gene. Quantitative real-time PCR and western blots were used to measure expression levels and PCR products were sequenced. Results： Results showed that the VEGFA mRNA and protein expression in heart, liver and kidney of TP was higher than that in YH and YL. In addition, the mRNA sequence of the pig VEGFA gene was conserved among pig breeds, and only five SNPs were found in the 5＇-flanking region of the VEGFA gene, the allele frequency distributions of the 5 SNPs were not significantly different between the TP, Yorkshire （YL）, and Diannan small-ear （DN） pig populations. Conclusion： In conclusion, the Tibetan pig showed high tissues, which suggests that the VEGFA gene may play a levels of VEGFA gene expression in several hypoxic major functional role in hypoxic adaptation.

Transgenic Pigs Carrying a Synthesized Fatty Acid Desaturase Gene Yield High Level of ω-3 PUFAs

Polyunsaturated fatty acids （PUFAs） are essential for normal growth in mammals, especially the ω-3 PUFAs, which play important roles in preventing several life-threatening diseases, such as coronary heart disease and diabetes. In this study, we aimed to investigate whether the sFat-1 gene from Caenorhabditis briggsae could be functionally expressed in transgenic pigs, and whether the transgenic could synthesize high quality ω-3 PUFAs endogenously. In this study, a gene construct consisting of CMV promoter and 1.9 kb cDNA of ω-3 fatty acid desaturase gene （sFat-1） from C. briggsae was injected into the male pronucleus of pig embryos by microinjection. The piglets were screened for the transgene by PCR, Southern blot and reverse transcription-PCR analysis. Pigs that give positive results were mated with wild-type pigs to produce the next generation and the transmission of transgene was examined by PCR analysis. Fatty acids compositions of various tissues in the transgenic pigs were then analyzed by gas chromatograph. A total of 878 embryos were transferred into 42 recipients, among which 29 successfully got pregnant and gave birth to a total of 162 piglets, and 8 of them were identified to be transgenic. Fatty acid compositions in the transgenic pigs were altered, and the levels of ω-6：ω-3 ratios were decreased from 14.53 in the control to 2.62 in Fat-1 transgenic pigs. A number of primary sFat-1-transgenic pigs were bred in this study, which lays the foundation for cultivation of new varieties of transgenic pigs.

Genetic Variation of EPAS1 Gene in Tibetan Pigs and Three Low-Altitude Pig Breeds in China

Endothelial PAS domain protein 1（EPAS1）, also called hypoxia-inducible factor-2, is a key regulatory factor of hypoxic responses and plays an essential role in high-altitude adaptation in mammalian species. In this study, polymorphisms of EPAS1 were detected in 217 individuals from 2 Tibetan pig populations and 3 low-altitude pig breeds by DNA pooling, PCR-SSCP, PCR-RFLP and DNA sequencing methods. A total of 14 synonymous polymorphisms were identified in the coding region. The analysis suggested that SNP1（G963A）, SNP7（C1632T）, SNP10（G1929A） and SNP11（G1947A） showed potential association with high-altitude environment because of their particular variation patterns in Tibetan pigs. Linkage disequilibrium（LD） of these SNPs was analyzed. One common LD block including 5 SNPs clustering in exon 12 was identified in all studied pig populations. Haplotype H1（AGGTC） in LD block was dominant in Tibetan pigs（76.6 and 74.2% in Linzhi（LZ） and Chayu（CY） pigs, respectively） and segregated at higher frequency than that in low-altitude pig breeds（52.3, 58.7 and 56.2% in Wuzhishan（WZS）, Min（M） and Laiwu（LW） pigs, respectively）, indicating that H1 may relate to adaptation to high altitude in Tibetan pigs. These findings raise hope that EPAS1 gene can be a candidate gene that involved in adaptation of high altitude in Tibetan pigs.

Generation of tryptophan hydroxylase 2 gene knockout pigs by CRISPR/Cas9-mediated gene targeting

Unbalanced brain serotonin(5-HT) levels have implications in various behavioral abnormalities and neuropsychiatric disorders. The biosynthesis of neuronal 5-HT is regulated by the rate-limiting enzyme, tryptophan hydroxylase-2(TPH2). In the present study, the clustered regularly interspaced short palindromic repeat(CRISPR)/CRISPR-associated(Cas) system was used to target the Tph2 gene in Bama mini pig fetal fibroblasts. It was found that CRISPR/Cas9 targeting efficiency could be as high as 61.5%, and the biallelic mutation efficiency reached at38.5%. The biallelic modified colonies were used as donors for somatic cell nuclear transfer(SCNT) and 10 Tph2 targeted piglets were successfully generated. These Tph2 KO piglets were viable and appeared normal at the birth.However, their central 5-HT levels were dramatically reduced, and their survival and growth rates were impaired before weaning. These Tph2 KO pigs are valuable large-animal models for studies of 5-HT deficiency induced behavior abnomality.

Genetic Effects of H-FABP Gene on Some Pig Economic Important Traits in a F2 Resource Population

The F2 design was used in construction of the pig resource population, and 14 economic important traits of 119 F2 offspring were measured. The polymorphisms of heart fatty acid binding protein gene (H-FABP) were detected by PCR-RFLP. The effects of different H-FABP genotypes were analyzed by a fixed model. The results showed that, the carcass composition traits were affected by H-FABP gene significantly, backfat thickness alive, carcass backfat thickness between 6th - 7th rib, and average carcass backfat thickness, of different H-FABP genotypes were significantly different (P<0. 05). The dominant effects on the traits demonstrated that the gene affected the carcass composition traits overdominantly. The results also showed that H-FABP gene affected the growth traits and meat quality traits, and the pH, of different H-FABP genotypes was significantly different.

Molecular characterization and tissue expression profile of the Dnmts gene family in pig

DNA methyltransferases（Dnmts）comprise a family of proteins which involved in the establishment and maintenance of DNA methylation patterns.In pig,the molecular characterization and tissue expression profile of Dnmt gene family are not clear.To solve this problem,reverse transcriptase PCR and rapid amplification of c DNA ends were used to clone the sequences of the porcine Dnmt2 and Dnmt3b genes.Furthermore,the m RNA expression profiles of Dnmt1,Dnmt2,Dnmt3a and Dnmt3b genes from 54 adult tissues and 2 entire fetuses of Rongchang pig were analyzed by quantitative real-time PCR（q RT-PCR）.As a result,the lengths of porcine Dnmt2 and Dnmt3b gene c DNAs were 1 227 and 2 559 bp with cytosine-C5specific DNA methylase domain,respectively.The four Dnmt genes were highly expressed in longissimus dorsi muscle（P〈0.01）.Dnmt1 is highly expressed in heart（P〈0.01）and Dnmt 2 shows its preference in liver and seminal vesicle tissue（P〈0.01）.Dnmt3a and Dnmt3b are highly expressed in the two fetus stages（P〈0.01）.All these results suggested that each gene has its specific expression profile,and deeper study is required to dig more details between the methylation level and Dnmt family m RNA expressions in different tissues.

Imprinting Analysis of RTL1 and DIO3 Genes and Their Association with Carcass Traits in Pigs (Sus scrofa)

Imprinted genes play significant roles in the regulation of fetal growth, development, function of the placenta and postnatal behavior in mammals, but little is known in pigs. In order to investigate the imprinting status of porcine retro-transposon like 1 （RTL1） and type 3 iodothyronine deiodinase （DIO3） genes, DNA or RNA samples of the parents and F1 animals, generated with reciprocal crosses between Large White and Meishan breeds, were isolated, and analyzed by reverse transcription polymerase chain reaction restriction fragment length polymorphism （RT-PCR-RFLP）. The results demonstrated that the RTL1 gene was paternally expressed in 10 tissues, such as the skeletal muscle, heart, spleen, liver, kidney, lung, stomach, fat, small intestine and brain, and D103 gene exhibited paternal expression in the skeletal muscle, heart, spleen, lung, stomach, and brain, in 2-month-old pigs. The association of RTL1 and DI03 with carcass traits was further analyzed in the F2 population of Large White×Meishan pigs. The statistical results showed that the R TL1 A1101G polymorphism （EU781029） was significantly associated with lean meat percentage （LMP） and fat meat percentage （FMP） （P〈0.05）, while the D103 A744C polymorphism （AY533208） was not significantly associated with any carcass traits. These results indicate that the imprinting status of RTL1 and DIO3 is well kept across the mammalian species, and porcine RTL1 may have important roles in muscle growth and fat deposition.

Identifying the complex genetic architecture of growth and fatness traits in a Duroc pig population

In modern pig breeding programs,growth and fatness are vital economic traits that significantly influence porcine production.To identify underlying variants and candidate genes associated with growth and fatness traits,a total of 1067 genotyped Duroc pigs with de-regressed estimated breeding values(DEBV)records were analyzed in a genome wide association study(GWAS)by using a single marker regression model.In total,28 potential single nucleotide polymorphisms(SNPs)were associated with these traits of interest.Moreover,VPS4 B,PHLPP1,and some other genes were highlighted as functionally plausible candidate genes that compose the underlying genetic architecture of porcine growth and fatness traits.Our findings contribute to a better understanding of the genetic architectures underlying swine growth and fatness traits that can be potentially used in pig breeding programs.

Effects of the Ratio of Lysine to Digestible Energy Level in the Diet on the Expression and Activity of Transcription Factors Involved in Lipogenesis in Rongchang Pigs

This study was conducted to determine the effects of varying the ratio of lysine to digestible energy level On the activity and gene expression of the transcription factors peroxisome proliferator-activated receptor-γ （PPAR-γ） and CCAAT/enhancer-binding protein-or and -β （C/EBP-α and C/EBP-β） to better understand the regulatory mechanisms controlling adipogenesis in fat and muscle tissue of the Rongchang pig. A total of 144 castrated Rongchang pigs weighing approximately 20 kg were used in a 2 ×2 factorial design experiment. Diets were formulated to contain a high （14.22 MJ/kg） or low （13.11 MJ/kg） digesti- ble energy （DE） level. Within each energy level, pigs were fed diets containing a high lysine： DE ratio （0.67,0. 53, or 0. 42） or a low lysine ： DE ratio （0.49,0.38 ,or 0.30） during the periods from 20 to 50 kg, 50 to 80 kg, and 80 kg to slaughter, respectively. Each diet was fed to six replicate pens, each containing nine pigs. When the pigs reached average live weights of 20,35,60, and 90 kg ,one pig from each of the replicates was chosen at random and slaughtered.Samples of back fat and longissimus dorsi muscle were collected for the assessment of transcriptional factor. The results showed that feeding a high DE level significantly increased （ P 〈 0.05 ） the expression of PPAR-T at 60 and 90 kg in muscle and at 35,60, and 90 kg in back fat. Energy level also significantly increased the expression of C/EBP-fl at 35 and 60 kg in both muscle and back fat （ P 〈 0.05 ）. Higher dieta- ry lysine increased the expression of C/EBP-fl in muscle at 35 and 90 kg （ P 〈 0.05）, but decreased the expression in back fat at 35 （P = 0.03 ） and 90 kg （P = 0.09）. The lysine level increased the expression of PPAR-3~ in muscle at 60 kg only. Energy level and lysine content had no significant effects on promote the activity of PPAR-γ, C/EBP-α, or C/EBP-β either in muscle or in back fat at any level of the body weights tested. Collectively, these data indicated that dietary energy density and lysine level were equally important for lipid deposition in muscle tissue, whereas dietary energy density was more important than lysine level for fat deposition in fat tissue.

BTG1 as a New Candidate Gene for Muscle Growth in Pigs: Cloning,Expression and Association Analysis

BTG1 （B-cell Translocation Gene 1） , a member of the BTG / TOB （Transducer of ErbB-2） family of anti-proliferation factors,has been proven to have an unfavorable effect on muscle fiber growth in several species. The porcine BTG1 gene was cloned and its 5＇ flanking promoter region sequence, and characterized the expression patterns in different tissues of adult pigs and in fetal skeletal muscle at different developmental stages in two breeds. The tissue distribution pattern analyses revealed that the mRNA of porcine BTG1 was ubiquitously expressed in the six tissues of both Landrace and Tongcheng pigs. Real-time quantitative reverse transcriptase-PCR results showed that BTG1 mRNA expression levels were significantly different among the three fetal ages in Tongcheng pigs,while no significant differences were found among the three ages in Landrace pigs. Furthermore,the expression of BTG1 in Landrace pigs was significantly lower than in Tongcheng pigs at all three ages. The temporal expression profiles of the BTG1 gene in mouse myoblast C 2 C 12 cells were shown to be consistent with those of the myogenin gene. A single nucleotide polymorphism （SNP） ,g. 281C 〉 T,was identified in the 3＇UTR and allele frequencies were detected in seven pig breed populations. Significant associations were found between the g. 281C 〉 T polymorphism and growth and meat quality traits. Our results indicate that the porcine BTG1 gene could play a potential role in markerassisted selection and as such may be a gene of economic importance.

Effects of SLA-DQA Gene on Birth Weight and 30-Day-Old Weight in Piglets

The genetic polymorphism of SLA-DQA gene was investigated by PCR-RFLP. The effects of SLA.DQA gene on birth weight and 30-day-old weight were analyzed in 250 individuals of FI hybrid pig （ Heilongjiang wild boar x Beijing Black sow）. The analysis revealed four poly- morphic loci in the SLA-DQA gene, but only the Pvu II locus in exon 2 of SLA-DQA gene （ BB genotype） greatly increased the 30-day-old weight of piglets.

Study of Swine Leukocyte Antigen Class I-3 (SLA-3) Gene for Inbreeding Wuzhishan Pig

To elucidate the structure of SLA-3 alleles on inbred line of Wuzhishan pig （WZSP） population, we examined the partial exon 1, completed exon 2, and partial exon 3 of SLA-3 loci using the reverse transcription-polymerase chain reaction （RT- PCR） and the sequencing-based method in 32 WZSPs. According to pedigree and amplification results, PCR products of 8 WZSPs were selected to clone and sequence. Nine different nucleotide sequences were obtained. After comparing the DNA and protein sequences of the WZSPs SLA-3 alleles with the published GenBank SLA sequences, it was found that the SLA-3 alleles in WZSPs were all novel, but there were very few variations among them. Comparision of SLA-3 and HLA-A protein sequences indicated that there was more sequence homology. Meanwhile, the construction of a phylogenetic tree using the nucleotide sequences of 23 SLA-3 alleles and 1 HLA-A allele represented that the WZSP population owns its unique genetics resource. In this study, the alleles of SLA-3 on WZSP group were successfully detected and analyzed, which provided the firm basis on the genotype of SLA-3 for breeding specific haplotypes WZSPs.

Study on pig growth hormone gene polymorphisms in western meat-type breeds and Chinese local breeds

Chinese Meishan and Jiangquhai pigs are two of the most prolific pigs in the world, but their growth rate is lower than that of Duroc, Landrace and Pietrain pigs. It is suggested that growth rate is regulated by growth hormone. The objective of the current study was to analyze the porcine growth hormone (p GH) gene polymorphisms based on the polymerase chain reaction restriction fragment-length polymorphism method (PCR-RFLP) for three western meat-type breeds (Duroc, Landrace and Pietrain) and two local Chinese pigs (Meishan and Jiangquhai) . Five polymorphic restriction sites were detected with the ApaI, MspI, BspI and HhaI restriction enzymes in two amplified fragments (605 bp, - 119 to + 486; 506 bp, + 206 to + 711).Breed difference was found only in the 506 bp fragment. There was no difference in allelic frequencies of BspIand HhaI restriction sites among the five breeds ( P > 0.05) . Landrace and Meishan pigs lacked allele G3 of Msp I site. The allele G3 frequency of restriction Msp I site of the 506 bp fragment in Pietrain pigs was higher than that in Duroc and Jianquhai pigs (P < 0.001 ). For ApaI site, the Meishan pigs lacked allele G1 i no difference was found in allelic frequencies among Pietrain, Duroc, Landrace and Jiangquhai pigs (P >0.05) . This new and rapid PCR-RFLP typing method is an attractive tool for analysis of porcine growth hormone gene restriction sites. The differences in MspI and ApaI restriction sites may explain the growth difference between the foreign meat-type breeds above mentioned and local Chinese pigs.