SNP (Single Nucleotide Polymorphism) molecular marker related to pig nipple number character and application thereof

Abstract

The invention belongs to the technical field of molecular biotechnology and molecular markers, and discloses a pig nipple number character related SNP molecular marker and application thereof, the site of the SNP molecular marker corresponds to the nucleic acid site at the 103001352bp site of the No.7 chromosome of the international pig reference genome Sscrofa11.1 version sequence, and the site is Ggt; and A basic group mutation. The SNP molecular marker associated with the nipple number character of the large white pig can be applied to genetic improvement of the growth and reproduction character of the large white pig, provides a new genetic marker resource for molecular marker-assisted selection of the nipple number character of the large white pig, can be applied to breeding of sows with high lactation capacity and high piglet survival rate, accelerates the breeding process, and improves the breeding efficiency. The reproductive performance of offspring large white pigs is improved.

Description

Technical Field

[0001] The present invention relates to the field of molecular biotechnology and molecular marker technology, in particular to SNP molecular markers related to pig nipple number traits and applications thereof. Background Art

[0002] The survival rate of piglets from birth to weaning has always been an important issue of concern in the pig industry (doi: 10.1093 / tas / txad100). In recent years, genetic improvement of reproductive traits has mainly focused on traits related to litter size. With the continuous genetic improvement of pig litter size traits, the total litter size of pigs has continued to increase. However, relevant studies have shown that the teat number trait is weakly negatively genetically correlated with the litter size trait. In actual production, too many litters increase the lactation pressure of sows in disguise, and the survival rate of piglets after birth is significantly reduced. It turns out that the selection of total teat number may not keep up with the number of live piglets born in high-yield genetic lines. Therefore, the total teat number of commercial sows is an important indicator of pig reproductive performance.

[0003] The teat number trait is a complex trait that is regulated by multiple genes and has low heritability. Therefore, the use of molecular markers for assisted breeding is a more effective selection method. Single nucleotide polymorphisms (SNPs), as single base variations in the genome, are highly stable and easy to detect in genetic transmission. Therefore, they can be used as molecular auxiliary markers for group breeding and breed protection. Marker-assisted selection can achieve early breeding, thereby improving the teat number and lactation capacity of sows, and ultimately optimizing the reproductive performance of sows.

[0004] However, there are few SNP molecular markers related to the nipple number trait of Large White pigs that have been discovered so far, and they cannot effectively guide the breeding of pigs with multiple nipples and high lactation ability. Therefore, the existing technology needs to be further improved. Summary of the invention

[0005] In response to the above problems, the present invention provides a SNP molecular marker related to the pig nipple number trait and its application. The SNP molecular marker related to the pig nipple number trait can be used in the selection or auxiliary selection of pigs with multiple nipples and total litter size traits, and can be used for the early selection of high-quality pig breeding, shortening the breeding cycle, and accelerating the population improvement process.

[0006] To solve the above problems, this application provides the following technical solutions: In the first aspect, the present application discloses a SNP molecular marker related to the pig nipple number trait, wherein the SNP molecular marker site corresponds to the nucleic acid site at the 103001352bp site of chromosome 7 of the international pig reference genome Sscrofa11.1 version sequence, and the site is a G>A base mutation.

[0007] The present invention uses ear samples from 1,000 Large White sows to extract DNA, conduct quality inspection, and use high-density chips for genotyping to obtain genotype data. The above-mentioned SNP molecular markers significantly associated with the total teat number of Large White pigs were screened out through the MVP package of R language combined with mixed linear model (MLM), generalized linear model (GLM) and FarmCPU model, providing new molecular markers for the selection and improvement of the total teat number trait of Large White pigs.

[0008] The correlation between the SNP molecular marker at the nucleic acid site at the 103001352bp site of chromosome 7 and the total number of teats of Large White pigs reached a significant level. The experimental results show that the GG type is more significant than the AA type, and the GG type is more significant than the AG type, indicating that the allele G is beneficial to the total number of teats. It provides a new genetic basis for the related research of this trait and has important guiding significance for the breeding of Large White pigs.

[0009] Optionally, the upstream and downstream nucleotide sequences of the SNP molecular marker site related to the pig teat number trait are as shown in SEQ ID NO: 1, and the SNP molecular marker is located at the 113th position R of the sequence, which is a non-synonymous mutation of G or A.

[0010] Detailed description: The sequence shown in SEQ ID NO: 1 is the upstream and downstream 150bp nucleotide sequence of the SNP molecular marker CNC10072084 associated with the total nipple number of Large White pigs screened by the present invention. The nucleotide sequence is 267bp in length. There is an A / G allele mutation at the R at the 113th base of the sequence. The mutation at this site can cause polymorphism in the nucleotide sequence where the CNC10072084 molecular marker site is located.

[0011] In the second aspect, the present application also provides the application of the above-mentioned SNP molecular markers related to the pig nipple number trait in pig genetic breeding. Based on the above content, it can be seen that the correlation between the above-mentioned SNP molecular markers and the pig nipple number trait is significant. By identifying the genotype of the molecular marker site, the nipple number trait can be analyzed and selected, and thus applied to the screening and breeding of excellent breeding pigs, which has important guiding significance for the breeding of Large White pigs.

[0012] In a third aspect, the present application also provides a method for breeding / assisting breeding pigs with more / fewer nipples using the aforementioned SNP molecular markers associated with the pig nipple number trait, the method comprising the following steps: 1) Detect the SNP molecular marker related to the above-mentioned pig nipple number trait at the 103001352bp site of chromosome 7 of the pig genome by the following primer pair or a probe containing the molecular marker site, and determine whether the base of the site is G or A, thereby determining whether the genotype of the site of the Large White pig to be tested is GG, AG or AA; 2) Then select the corresponding genotype of Large White pigs according to the breeding objectives for the next step of selection and / or breeding.

[0013] According to step 1) of the method, if pigs with multiple nipples are selected, individuals with the allele type GG or the allele type GG and / or AG detected in step 1) are selected as breeding pigs, and breeding pig individuals with the AA genotype are eliminated.

[0014] The experiment found that the total number of nipples in the GG-type Large White pigs was significantly higher than that in the AG-type, and the total number of nipples in the AA-type Large White pigs was the least. Figure 5 shown.

[0015] Optionally, in step 1) of the method, if pigs with oligonipple trait are screened, individuals with AA allele type detected in step 1) are selected.

[0016] In a fourth aspect, the present application further provides an application of the aforementioned SNP molecular marker in breeding a high-nipple number pig strain, comprising the following steps: (1) Detecting the aforementioned SNP molecular markers related to the pig nipple number trait in the reserve breeding pigs by using the following primer pairs or probes containing the molecular marker sites; (2) Selecting individuals with the GG or GA genotype detected in step (1) as breeding pigs, and mating the breeding boars and sows; (3) The aforementioned SNP molecular markers are detected in the piglets born from the mating in step (2), the individuals with the genotype of the locus being GG or GA are retained, and the individuals with the genotype of AA are eliminated, thereby breeding a pig strain with a large number of nipples and high reproductive performance.

[0017] Optionally, the application further comprises: repeating the operations of steps (2) to (3) with the individuals bred in step (3), thereby selecting breeding pig individuals with molecular marker genotypes of GG or AG in the offspring, and eliminating individuals with AA genotype, so as to increase the frequency of allele G in the offspring pig population generation by generation, thereby increasing the number of nipples of the offspring pigs.

[0018] In a fifth aspect, the present application also provides a primer pair for identifying the aforementioned SNP molecular markers associated with the pig nipple number trait, the primer pair comprising: an upstream primer F1 with a sequence as shown in SEQ ID NO: 2 and a downstream primer R1 with a sequence as shown in SEQ ID NO: 3.

[0019] In a sixth aspect, the present application also provides the above-mentioned SNP molecular markers related to the pig nipple number trait, and the aforementioned primer pairs for screening or identifying the pig multiple nipple number trait, and are applied to the breeding of pig multiple nipple number traits and high lactation trait varieties.

[0020] In a seventh aspect, the present application also provides a method for obtaining SNP molecular markers related to the total nipple number of Large White pigs, the method for obtaining is: (1) Performing quality control and analysis on the total DNA of pigs to obtain genotype data; collecting the total teat number data of individual Large White pigs and using it as the phenotype, using genome-wide association analysis technology to obtain SNPs significantly associated with the total teat number trait of Large White pigs for quality control. The quality control criteria are: removing individual detection rate < 80%, SNP detection rate < 80%, minimum allele frequency < 0.01, Hardy-Weinberg equilibrium p value >= 10 -5 , unknown or repeated SNPs in chromosomes; (2) The whole genome association analysis was then used to screen SNPs, key candidate genes and molecular markers associated with the number of pig nipples. The mixed linear model used in this analysis was: Y ijklnm =μ+G i +HYS j +Line k +Parity l +ID m +ε ijklnm Where i is the original phenotypic value of the total nipple number trait of the mth individual; μ is the population mean; G i is the CNC10072084 molecular marker genotype effect (fixed effect); HYS j is the combined effect of birth place, birth year and birth season (fixed effect); Line k is the strain effect (fixed effect); Parity l is the parity effect (fixed effect); ID m is an individual additive effect (random effect), which is assumed to be normally distributed: id~N(0,σ id 2 ), σ id 2 represents the individual effect variance; ε ijklnm is the model residual effect, which obeys the normal distribution: ε~N(0,σ ε 2 ), σ ε 2 represents the residual variance.

[0021] The above method was used to screen out the SNP molecular marker related to the aforementioned pig nipple number trait. The SNP marker was located at the nucleic acid site at the 103001352bp site on chromosome 7, which was a G>A base mutation.

[0022] The present invention has the following beneficial effects: 1. The present invention screened and identified a SNP site and molecular marker associated with the number of teats in Large White pigs for the first time, providing an effective candidate gene for improving the excellent growth and reproduction traits of Large White pigs. It was found that the number of teats in Large White pigs with GG genotype at this site was higher than that in Large White pigs with GA genotype, and the number of teats in Large White pigs with GA genotype was higher than that in Large White pigs with AA genotype. Figure 5 Therefore, this locus can be used in the genetic improvement of growth and reproduction traits of Large White pigs, and provides a new genetic marker resource for molecular marker-assisted selection of pigs with multiple nipples.

[0023] 2. The present application also provides a primer and a kit for identifying the above-mentioned SNP molecular markers related to the total nipple number of Large White pigs, and ultimately establishes an efficient and accurate molecular marker-assisted breeding technology, which is applied to the genetic improvement of Large White pig breeders to increase the total nipple number, thereby enabling the rapid and accurate selection and breeding of Large White pigs, accelerating the breeding process, and improving the reproductive performance of future generations of Large White pigs.

[0024] 3. By detecting the genotype of the above-mentioned SNP molecular markers related to the number of nipples to assist in the selection of Large White sows with a large number of nipples, the total number of nipples can be increased, the nutritional level of piglets can be improved, and the number of weaned piglets can be increased by selecting a core group of Large White sows with homozygous GG.

[0025] 4. The present invention can detect the genotype of Large White pigs by using gene chip technology in vitro, and evaluate the nipple number of Large White pigs for non-diagnostic purposes. Compared with the current methods such as PCR-RFLR, the present invention has the outstanding advantages of being simple, rapid, highly sensitive and specific.

[0026] 5. The invention also provides a method for screening candidate markers and genes related to the number of teats in Large White pigs based on a method of whole genome association analysis. The loci of SNPs related to the number of teats screened and identified by this method can be used as molecular markers for the selection of excellent traits of Large White pigs, which helps to accelerate the genetic improvement of the production performance of Large White pigs. The above screening method has the characteristics of simple operation, comprehensive coverage, and high accuracy of selected markers, and also provides technical support for the genetic analysis of other important economic traits of livestock and poultry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a Manhattan plot of the genome-wide association analysis of the present invention. The black marker is the SNP molecular marker CNC10072084 screened by the present invention, which is located on chromosome 7 of Large White pigs; Figure 2 This is the QQ plot of genome-wide association analysis of Landrace pig nipple number; Figure 3 This is the SNP density distribution map used in the whole gene association analysis of Landrace pig nipple number; Figure 4This is the PCA graph involving 1000 Large White pig genomes; Figure 5 This is the distribution diagram of the total nipple number trait of individuals with different genotypes related to the nipple number of Landrace pigs. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. In the present invention, unless otherwise specified, the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are conventional methods in the art unless otherwise specified.

[0029] Example 1 Screening of SNP molecular markers associated with nipple number in Large White pigs 1. Phenotype-pedigree data collection Experimental animals: The basic research population of this experiment was French Large White sows, which came from the Large White Breeding Pig Farm of Beijing Zhongyu Breeding Pig Co., Ltd.

[0030] The basic breeding population of this experiment includes 1000 Large White pigs, of which the phenotypic data such as the number of left nipples and the number of right nipples of 1000 Large White pigs were recorded. After filtering the abnormal phenotypic data, a total of 1000 total nipple observations were obtained for phenotype-genotype association analysis.

[0031] The formula for calculating the total number of nipples is: total number of nipples = number of left nipples + number of right nipples.

[0032] 2. Genotyping and quality control (1) Ear tissue samples were collected from 1,000 Large White sows, DNA was extracted, and genotyping was performed using the pig breeding 50k SNP chip (SMIC No. 1 breeding chip), obtaining 31,625 SNP markers covering the entire genome.

[0033] (2) For all SNP markers located on the 18 chromosomes, Plink1.9 software was used for quality control, with the following standards: individual detection rate>=80%; SNP detection rate>=80%, minimum allele frequency>=0.01, Hardy-Weinberg equilibrium p value>=10 -5 Missing genotypes were filled using Beagle5.1 software.

[0034] Based on the above quality control criteria, 1000 Large White pigs and 31625 SNP markers were used for genome-wide association analysis, among which 1000 Large White pigs had both total teat number phenotypic data and genotypic data.

[0035] 3. Genome-wide association analysis of total teat number in Large White pigs (1) GWAS analysis was performed using the MLM model, GLM model and farmCPU in the MVP software package in the R statistical environment to obtain SNP markers that were significantly associated with the total nipple number trait detected by various methods. SNP markers detected by at least two of the methods were selected as candidate SNPs.

[0036] (2) For the p-values ​​of all markers, -log10 was used to draw the Manhattan plot, and three analysis methods, including MLM, GLM and farmCPU models, were combined to display and screen the SNP markers with significant association.

[0037] like Figure 1 As shown, in Large White pigs, there is a locus CNC10072084 on chromosome 7 that significantly affects the total effective nipple number.

[0038] 4. Association analysis between CNC10072084 molecular marker typing results and total papilla number (1) Experimental methods: A mixed linear model (MLM) was used to conduct an association analysis between the CNC10072084 molecular marker and the total teat number of French Large White pigs. The specific model is as follows: Y ijklnm =μ+G i +HYS j +Line k +Parity l +ID m +ε ijklnm Where i is the original phenotypic value of the total nipple number trait of the mth individual; μ is the population mean; G i is the CNC10072084 molecular marker genotype effect (fixed effect); HYS j is the combined effect of birth place, birth year and birth season (fixed effect); Line k is the strain effect (fixed effect); Parity l is the parity effect (fixed effect); ID m is an individual additive effect (random effect), which is assumed to be normally distributed: id~N(0,σ id 2 ), σ id 2 represents the individual effect variance; ε ijklnm is the model residual effect, which obeys the normal distribution: ε~N(0,σ ε 2 ), σ ε 2The F test was used to analyze the significance of the total nipple number trait among the three genotypes. The results are shown in Table 1.

[0039] Table 1 Effects of different genotypes of CNC10072084 marker on the total teat number of Large White pigs Number of individuals genotype Total nipples 292 GG 13.86±0.082 492 GA 13.55±0.070 216 AA 13.21±0.109 P <0.0001 AA-GA <0.025 AA-GG <0.0001 GA-GG <0.031 Table 1 Description: p < 0.05 indicates significant difference; p < 0.01 indicates extremely significant difference.

[0040] (2) Experimental results and analysis From the results in Table 1, we can see that for the CNC10072084 marker site on chromosome 7 of the molecular marker, the average total number of papillae in GG type individuals is higher than that in AA type and AG type individuals, which indicates that the homozygous GG type is beneficial to the average total number of papillae. GG type is significantly higher than AA type, and GG type is significantly higher than AG type, which indicates that allele G is beneficial to the total number of papillae.

[0041] The total number of teats is an important indicator for measuring the reproductive performance of large white pigs. A higher total number of teats indicates better reproductive performance of large white pigs. Therefore, eliminating large white pigs with the AA genotype can bring more economic benefits. In the actual breeding process, the frequency of the G allele at this locus can be increased generation by generation by eliminating AA large white sows and retaining GG large white sows, thereby breeding a pig strain with a high number of teats and high reproductive performance.

[0042] The gene results obtained from the above experimental screening obtained a SNP molecular marker CNC10072084 related to the total number of teats of Large White pigs. The molecular genetic marker is located at the 103001352 nucleic acid site of chromosome 7 of Large White pigs. This position is a G>A mutation, corresponding to the 113th nucleic acid site located in the nucleic acid sequence table SEQ ID NO: 1.

[0043] The nucleotide sequence shown in SEQ ID NO: 1 in the sequence table is a nucleotide sequence of about 150 bp upstream and downstream of the SNP molecular marker CNC10072084 associated with the total teat number of Large White pigs screened by the present invention, the nucleotide sequence length is 261 bp, and there is an A / G allele mutation at the 113th base of the sequence. The mutation can cause the nucleotide sequence shown in NC_010449.5 to produce polymorphism.

[0044] Example 2 Design of primers for identifying SNP molecular markers associated with the teat number trait of Large White pigs and application of the primers This example is the SNP site obtained in Example 1, the 103001352 nucleic acid site G / A of chromosome 7, and the upstream and downstream primers and amplified fragments are designed according to the site sequence. 1. Primer design of target gene sequence According to the target gene sequence, the optimized amplification primers were designed using primer design software. The primer pair sequences are as follows: Upstream primer F1: 5'-GCAGGGGTAGATAACTGCTG-3' (such as SEQ ID NO: 2) Downstream primer: R1: 5'-TGGTGCAAAACACCACACAAT-3' (such as SEQ ID NO: 3) 2. Large White Pig Genome Extraction Collect ear tissue samples or blood samples from Large White pigs to be tested, extract genomic DNA, and store them at -20°C for later use after quality and concentration testing.

[0045] 3. PCR amplification of SNP loci related to the number of teats in Large White pigs Using the extracted DNA as a template, the experiment selected a mixture of DNA samples of Large White pig blood genes to prepare a mixed pool DNA template, and used the above primers for PCR amplification.

[0046] The PCR amplification system (total volume 20.0 μL) is: 10.0 μL of 2xTaq PCR Master Mix, 0.5 μL of upstream primer (10 μmol / L), 0.5 μL of downstream primer (10 μmol / L), 1.0 μL of genomic DNA template, and 8.0 μL of ddH2O.

[0047] The PCR amplification procedure is: Pre-denaturation at 95°C for 5 min; denaturation at 95°C for 30 s, annealing at 55°C for 30 s, extension at 72°C for 1 min, for a total of 30 cycles; extension at 72°C for 5 min.

[0048] The PCR products were detected by 1.5% agarose gel electrophoresis and sequenced by Sangon Biotechnology (Shanghai) Co., Ltd.

[0049] 4. Sequencing and analysis of amplified products The PCR product was detected by agarose gel electrophoresis, and the target fragment size was 191 bp. The amplified product was sent for sequencing, and the sequence of the amplified product was obtained by sequencing. The nucleotide sequence of the target fragment is shown in SEQ ID NO: 4. The sequencing result was compared and analyzed with the relevant gene fragment of Large White Pig in GenBank (as shown in SEQ ID NO: 1) to determine whether the genotype of the target SNP site related to the number of nipples in the sequence is GG, AG or AA.

[0050] According to the above results, large white pigs with more or fewer nipples are selected. If large white pigs with more nipples are selected, large white pigs with GG and AG genotypes are selected; if large white pigs with fewer nipples are selected, large white pigs with AA genotypes are selected.

[0051] The experimental results show that the above primers can be effectively used to identify SNP molecular markers related to the teat number trait of Large White pigs, and can be widely used in the identification, screening and breeding of Large White pigs with teat quantity traits.

[0052] In addition, those skilled in the art can design other primers for amplifying the molecular marker or probes for identifying the molecular marker according to the molecular genetic marker of the present invention, so as to detect the genetic marker, for example, by PCR amplification to obtain the molecular genetic marker, and then by cloning and sequencing to obtain the corresponding sequence, or by Bsm-RFLP polymorphism for detection. Therefore, the present invention also includes primers for amplifying the molecular genetic marker or probes for identifying the molecular genetic marker, and test kits containing the primers or probes, etc.

[0053] Example 3 Application of the molecular genetic markers of the present application in Large White pig breeding This embodiment provides a method for applying the molecular genetic markers of the present application to breeding or auxiliary breeding of large white pigs, and the method is specifically: (1) Extracting genomic DNA from Large White pigs, detecting the deoxynucleotide at position 103001352 of chromosome 7, and determining whether the deoxynucleotide at the position is A or G; (2) The genotype of the Large White pig to be tested is determined to be AA, AG or GG based on the genotype of the locus. Based on breeding requirements, Large White pigs with AA, AG or GG genes are selected for the next step of selection and / or breeding.

[0054] Specifically, if breeding large white pigs with multiple nipples, AA-type large white sows are eliminated and GG-type large white sows are retained to increase the allele frequency of G at this locus generation by generation. This is because the total number of nipples of homozygous GG-type large white pigs at this locus is higher than that of AA-type.

[0055] As can be seen from Table 1, the average total number of nipples per GG type Large White pig is 0.65 higher than that of AA type. If there are 10,000 breeding Large White sows, they can produce 7,000 more Large White piglets per litter. If these piglets are directly fattened to 100 kg and put on the market, and based on an estimated slaughter rate of 85%, 10,000 Large White sows can provide 595 tons of more Large White pork, which will bring huge economic income and effects to the company and increase its core competitiveness.

[0056] Example 4 A method for genetic improvement of large white pigs with multiple nipples This embodiment provides a method for genetic improvement of multi-nipple Large White pigs, the method comprising the following steps: (1) Detection of SNP molecular markers related to the above-mentioned pig nipple number trait in reserve breeding pigs: extract the genome respectively, and use the primers and methods of the above-mentioned Example 2 for detection.

[0057] (2) selecting individuals with a genotype of GG or GA at the SNP loci associated with the nipple number trait detected in step (1) as breeding pigs, and mating the breeding boars with sows; (3) The aforementioned SNP molecular markers are detected in the piglets born from the mating in step (2), the individuals with the genotype of the locus being GG or GA are retained, and the individuals with the genotype of AA are eliminated, thereby breeding a pig strain with a large number of nipples and high reproductive performance.

[0058] On the basis of the above, the following steps can be further performed: (4) Repeating the operations of steps (2) to (3) with the individuals bred in step (3), thereby selecting breeding pig individuals with molecular marker genotypes of GG or AG in the offspring and eliminating individuals with AA genotype, so as to increase the frequency of allele G at the SNP site related to the above-mentioned pig nipple number trait in the offspring pig population generation by generation, thereby increasing the nipple number of the offspring pigs.

[0059] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A SNP molecular marker associated with the pig nipple number trait, characterized in that: The SNP molecular marker site corresponds to the nucleic acid site at the 103001352bp site on chromosome 7 of the international pig reference genome Sscrofa11.1 version sequence, and the site is a G>A base mutation.

2. The SNP molecular marker associated with the pig nipple number trait according to claim 1, characterized in that: A 150 bp fragment upstream and downstream of the SNP site was taken as the upstream and downstream sequences showing its characteristics. The nucleotide sequence of the upstream and downstream sequences is shown in the sequence table SEQ ID NO:

1. The SNP molecular marker site is located at the 113th site R of the sequence, and there is a single base mutation G>A.

3. According to the characteristics of claim 1, SNP molecular markers can be used in the breeding of sows for the nipple number trait.

4. A method for breeding / assisting breeding of pigs with more / fewer nipples using the SNP molecular markers associated with the pig nipple number trait as claimed in claim 1, characterized in that: The following steps are involved: (1) Detecting the SNP molecular marker related to the pig nipple number trait as claimed in claim 1 at the 103001352bp site of chromosome 7 of the pig genome, and determining whether the base at the site is G or A, thereby determining whether the genotype of the site of the Large White pig to be tested is GG, AG or AA; (2) Based on the breeding objectives, select Large White pigs with corresponding genotypes for the next step of selection and / or breeding.

5. The method according to claim 4, characterized in that In step (2), if pigs with multiple nipples are selected, individuals with the allele type GG or the allele type GG and / or AG detected in step (1) are selected as breeding pigs, and breeding pig individuals with the AA genotype are eliminated.

6. The method according to claim 4, characterized in that In step (2), if pigs with oligonipple trait are selected, the individuals with AA allele type detected in step (1) are selected.

7. The use of the SNP molecular marker according to claim 1 in breeding a high nipple number pig strain, characterized in that: The application comprises the following steps: (1) Detecting the SNP molecular markers related to the pig nipple number trait as claimed in claim 1 or 2 in reserve breeding pigs; (2) Selecting individuals with the GG or GA genotype detected in step (1) as breeding pigs, and mating the breeding boars and sows; (3) The SNP molecular marker as described in claim 1 is detected in the piglets born from the mating in step (2) using a kit containing the following primer pair or a molecular probe containing the marker site, individuals with a genotype of GG or GA at the site are retained, and individuals with a genotype of AA are eliminated, thereby breeding a pig breed with a large number of nipples and high reproductive performance.

8. The use according to claim 7, characterized in that: Also includes: Repeat steps (2) to (3) with the individuals bred in step (3), so as to select breeding pig individuals with molecular marker genotypes of GG or AG in the offspring and eliminate individuals with AA genotype, so as to increase the frequency of allele G in the offspring pig population generation by generation and increase the number of nipples in the offspring pigs.

9. A primer pair for identifying the SNP molecular marker associated with the pig nipple number trait as claimed in claim 1, characterized in that: The primer pair comprises: an upstream primer F1 whose sequence is shown in SEQ ID NO: 2 and a downstream primer R1 whose sequence is shown in SEQ ID NO:

3.

10. A kit for detecting the SNP molecular marker according to claim 1, wherein: The kit contains the primer pair according to claim 8.

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