SNP (Single Nucleotide Polymorphism) site related to strength of pig immune system, related molecular marker and application of SNP site and molecular marker

Abstract

The invention belongs to the technical field of molecular biotechnology and molecular markers, and particularly relates to an SNP (Single Nucleotide Polymorphism) site related to the strength of a pig immune system, a related molecular marker and application of the SNP site. The SNP site corresponds to the 40842218bp site of a No.7 chromosome of an international pig reference genome version 11.1, the polymorphism of a base of the site affects the percentage content of conventional CD4-CD8 + CD3 + mononuclear T cells of pig blood, the related index of a GG genotype is larger than that of pig individuals of AG and AA genotypes, and the related index of the AG genotype is larger than that of pig individuals of AA genotypes. According to the invention, the problem of improving the immunity of pigs is solved by means of molecular breeding, and by optimizing the dominant alleles of the SNP, the frequency of the dominant alleles can be increased generation by generation, the percentage content of conventional CD4-CD8 + CD3 + mononuclear T cells of the pigs can be increased, the genetic modification breeding of the pigs can be accelerated, and the economic benefits of pig farms can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of molecular biotechnology and molecular marker technology. Specifically, the present invention relates to a SNP site related to the strength of pig immune system, a related molecular marker and its application. Background Art

[0002] In the pig breeding process, the strength of the immune system is an important consideration. As a key component of the immune system, the pig's CD4-CD8+CD3+ mononuclear T cells are closely related to the pig's disease resistance. When responding to viral, bacterial and parasitic infections, CD4-CD8+CD3+ mononuclear T cells play a vital role in the pig's anti-infection immunity. Therefore, in the pig breeding program, selecting individuals with a strong immune system and a strong CD4-CD8+CD3+ mononuclear T cell response can improve the disease resistance of the offspring of the breeding pigs. Summary of the invention

[0003] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a SNP site related to the strength of pig immunity or the percentage of CD4-CD8+CD3+ mononuclear T cells in blood routine, and to develop a SNP molecular marker related to the site.

[0004] The present invention also aims to provide a substance for detecting the polymorphism or genotype of SNP sites in the pig genome for use in any of the following: (1) identifying or assisting in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests; (2) screening or improving pig immune traits; and (3) pig breeding.

[0005] Another object of the present invention is to provide a primer composition and a kit for identifying the above-mentioned SNP molecular markers.

[0006] The purpose of the present invention is also to provide the application of the above primer pair and kit, and to provide a genetic improvement method for molecular marker-assisted breeding to improve pig immune traits.

[0007] The present invention is achieved in that:

[0008] A reagent for detecting a SNP site associated with the strength of a pig's immune system is used in identifying the percentage of CD4-CD8+CD3+monocyte T cells in a pig's blood routine test. The SNP site corresponds to the 40842218bp position of chromosome 7 of the international pig reference genome version 11.1 and is located in the CLIC5 gene. The polymorphism of the bases at the site affects the percentage of CD4-CD8+CD3+monocyte T cells in a pig's blood routine test. The percentage of CD4-CD8+CD3+monocyte T cells in a pig with the GG genotype at the SNP site is higher than that in a pig with the AG genotype and a pig with the AA genotype. The percentage of CD4-CD8+CD3+monocyte T cells in a pig with the AG genotype at the SNP site is higher than that in a pig with the AA genotype.

[0009] A reagent for detecting a SNP site associated with the strength of a pig's immune system is used in screening pigs with a trait of high percentage of CD4-CD8+CD3+monocyte T cells in routine blood tests, wherein the SNP site corresponds to the 40842218bp position of chromosome 7 of the international pig reference genome version 11.1 and is located in the CLIC5 gene; the polymorphism of the bases at the site affects the percentage of CD4-CD8+CD3+monocyte T cells in routine blood tests of pigs; the percentage of CD4-CD8+CD3+monocyte T cells in routine blood tests of pigs with the GG genotype at the SNP site is higher than those of pigs with the AG genotype and pigs with the AA genotype; the percentage of CD4-CD8+CD3+monocyte T cells in routine blood tests of pigs with the AG genotype at the SNP site is higher than that of pigs with the AA genotype.

[0010] A reagent for detecting a SNP site associated with the strength of a pig's immune system is used in genetic breeding to improve the percentage content of CD4-CD8+CD3+monocyte T cells in pig blood routine. The SNP site corresponds to the 40842218bp of chromosome 7 of the international pig reference genome version 11.1, and is located in the CLIC5 gene. The polymorphism of the bases at the site affects the percentage content of CD4-CD8+CD3+monocyte T cells in pig blood routine. The percentage content of CD4-CD8+CD3+monocyte T cells in pig blood routine of GG genotype pigs at the SNP site is higher than that of AG genotype pigs and AA genotype pigs. The percentage content of CD4-CD8+CD3+monocyte T cells in pig blood routine of AG genotype pigs at the SNP site is higher than that of AA genotype pigs.

[0011] A reagent for detecting SNP molecular markers related to the strength of the pig immune system in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests, characterized in that the nucleotide sequence of the SNP molecular marker is

[0012]

[0013] This SNP site is named (G\A) site, the nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AG or AA; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of GG genotype pigs is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of AG genotype pigs is higher than that of AA genotype pigs.

[0014] A reagent for detecting SNP molecular markers related to the strength of the pig immune system is used in screening pigs with a high percentage of CD4-CD8+CD3+ mononuclear T cells in blood routine, wherein the nucleotide sequence of the SNP molecular marker is

[0015]

[0016]

[0017] This SNP site is named (G\A) site, the nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AG or AA; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of GG genotype pigs is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of AG genotype pigs is higher than that of AA genotype pigs.

[0018] A reagent for detecting SNP molecular markers related to the strength of the pig immune system is used in genetic breeding to improve the percentage content of CD4-CD8+CD3+ mononuclear T cells in pig blood routine, wherein the nucleotide sequence of the SNP molecular marker is

[0019]

[0020] This SNP site is named (G\A) site, the nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AG or AA; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of GG genotype pigs is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of AG genotype pigs is higher than that of AA genotype pigs.

[0021] A method for detecting the strength of a pig's immune system comprises the following steps: detecting a SNP site located at 40842218 bp of chromosome 7 of version 11.1 of the international pig reference genome and located in the CLIC5 gene; identifying whether the single nucleotide at the SNP site is A or G; determining the genotype of the tested pig; analyzing and judging that the percentage content of CD4-CD8+CD3+monocyte T cells in the blood routine test of a GG genotype pig at the SNP site is higher than that of an AG genotype pig and an AA genotype pig; and the percentage content of CD4-CD8+CD3+monocyte T cells in the blood routine test of an AG genotype pig is higher than that of an AA genotype pig.

[0022] A primer composition for identifying a SNP site associated with the strength of a pig's immune system, comprising an upstream primer and a downstream primer, the nucleotide sequence of which is as follows:

[0023] Upstream primer: 5′-TGCTTTACTTCTGCCTTAGAGCAAT-3′;

[0024] Downstream primer: 5′-TCCTCCTCTTGCCAACCCAC-3′;

[0025] The SNP site corresponds to the 40842218bp of chromosome 7 of the international pig reference genome version 11.1, and is located in the CLIC5 gene. The percentage of CD4-CD8+CD3+mononuclear T cells in the blood of GG genotype pigs at the SNP site is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+mononuclear T cells in the blood of AG genotype pigs is higher than that of AA genotype pigs.

[0026] The primer combination is used to identify the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test.

[0027] The primer combination is used in screening pigs with a high percentage of CD4-CD8+CD3+ mononuclear T cells in blood routine.

[0028] The primer combination is used in genetically assisted breeding to improve the percentage content of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test.

[0029] A kit for identifying SNP sites associated with the strength of pig immune system, the kit comprising the aforementioned primer combination.

[0030] Preferably, the aforementioned kit further comprises at least one of a PCR reaction buffer, a Taq DNA polymerase and dNTPs.

[0031] We found through experiments that the G / A site at position 40842218 of chromosome 7 of pigs has a significant effect on the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests. The nucleotide sequence of this site is

[0032] This SNP site is named as (G\A) site. The nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AA or AG. The GG genotype is a homozygous form in which the nucleotide of the (G\A) site is G. The AA genotype is a homozygous form in which the nucleotide of the (G\A) site is A. The AG genotype is a heterozygous form in which the nucleotide of the (G\A) site is G and A.

[0033] Based on the SNP site, the present invention provides a method for identifying or assisting in identifying the percentage content of CD4-CD8+CD3+monocyte T cells in pig blood routine, and the present invention provides a method for screening the percentage content of CD4-CD8+CD3+monocyte T cells in pig blood routine.

[0034] According to the genotype identification or auxiliary identification, the percentage content of CD4-CD8+CD3+ mononuclear T cells in the blood routine of the screened pig includes at least one of the following:

[0035] (1) The percentage of CD4-CD8+CD3+monocyte T cells in the blood of pigs with a genotype of GG at the SNP site is greater than the percentage of CD4-CD8+CD3+monocyte T cells in the blood of pigs with a genotype of AA or AG at the SNP site.

[0036] (2) The percentage of CD4-CD8+CD3+monocyte T cells in the blood of pigs with AG genotype at the SNP site is greater than the percentage of CD4-CD8+CD3+monocyte T cells in the blood of pigs with AA genotype at the SNP site.

[0037] The present invention can be used for breeding pigs with strong immunity in pig breeding. Gene fragments are amplified by PCR, and the deoxyribonucleotide type at position 40842218 of chromosome 7 is sequenced to detect the genotype of the SNP site in the pig genome to be tested. Pigs with a genotype of GG at the SNP site of the pig genome are selected as parents for breeding to obtain piglets with stronger immunity or a higher percentage of CD4-CD8+CD3+monocyte T cells in blood routine.

[0038] The present invention provides a primer composition for detecting the polymorphism or genotype of the SNP site at position 40842218 of chromosome 7 in the pig genome, and also provides a kit including the primer composition. The primer composition can be used for:

[0039] (1) Products for identifying or assisting in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests;

[0040] (2) Products that improve pig immune traits;

[0041] (3) Products of pig breeding.

[0042] The present invention solves the problem of improving pig immunity by means of molecular breeding. By optimizing the dominant allele of the above SNP, the dominant allele frequency can be increased from generation to generation, the percentage content of conventional CD4-CD8+CD3+ mononuclear T cells in pigs can be increased, the genetic breeding of pigs can be accelerated, and the economic benefits of pig farms can be improved. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0044] The experimental methods in the examples are conventional methods unless otherwise specified, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the examples are all commercially available unless otherwise specified.

[0045] All animals in the examples are from the pig farm of the experimental base of this laboratory. The examples use the F2 generation individuals of the hybrid pigs obtained by hybridizing the Large White pigs and the Min pigs as experimental samples. The F2 generation individuals are hybrid first generation groups obtained by hybridizing the Large White pig boars and the Min pig sows, and the second generation obtained by self-crossing the hybrid first generation groups.

[0046] The percentage content of CD4-CD8+CD3+monocyte T cells in the routine blood of pigs in the embodiment refers to the percentage content of CD4-CD8+CD3+monocyte T cells in the routine blood of pigs at 240 days of age.

[0047] In order to establish a method to assist in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood, we conducted the following experiments.

[0048] 1. Screening of the G / A SNP site at position 40842218 on pig chromosome 7

[0049] Ear tissue samples were collected from 30 Damin hybrid pigs, and genomic DNA was extracted.

[0050] Upstream primer: 5'-TGCTTTACTTCTGCCTTAGAGCAAT-3'

[0051] Downstream primer: 5′-TCCTCCTCTTGCCAACCCAC-3′;

[0052] As amplification primers, PCR amplification was performed with the genomic DNA of the pig to be tested as the template DNA to obtain PCR products, which were then sequenced. Seqman software was used for comparison to obtain a differential site, named the (G\A) site, located at nucleotide 40842218 of pig chromosome 7. The nucleotide type of the (G\A) site is G or A, and the genotype is GG, AA or AG. The GG genotype is a homozygous body with the nucleotide of the (G\A) site being G. The AA genotype is a homozygous body with the nucleotide of the (G\A) site being A. The AG genotype is a heterozygous body with the nucleotide of the (G\A) site being G and A.

[0053] II. Correlation analysis between the (G\A) locus at position 40842218 of chromosome 7 and the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test

[0054] In order to determine whether the G / A site at position 40842218 of chromosome 7 of pigs is correlated with the percentage of CD4-CD8+CD3+monocyte T cells in pig routine blood, 489 F2 individuals of Damin pig hybrid were used as experimental materials. According to the above experimental method, the pig genome was amplified using upstream primers and downstream primers and then sequenced to determine whether the (G\A) site of each individual was GG genotype, AA genotype or AG genotype, the percentage of CD4-CD8+CD3+monocyte T cells in each individual's blood routine was measured, and correlation analysis was performed.

[0055] 1. Genotype

[0056] The GG genotype is homozygous for the nucleotide 40842218 of chromosome 7 of pigs, which is G;

[0057] The AA genotype is homozygous for the nucleotide 40842218 of chromosome 7 of pigs, which is A;

[0058] The AG genotype is a heterozygous form of A and G at position 40842218 of chromosome 7 of pig.

[0059] The nucleotide sequence containing the 40842218th position of the pig chromosome 7 is

[0060]

[0061] This SNP site is named as (G\A) site. The nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AA or AG. The GG genotype is a homozygous form in which the nucleotide of the (G\A) site is G. The AA genotype is a homozygous form in which the nucleotide of the (G\A) site is A. The AG genotype is a heterozygous form in which the nucleotide of the (G\A) site is G and A.

[0062] The results of the (G\A) locus genotype test of 489 experimental pigs showed that 157 were GG genotypes, 79 were AA genotypes, and 253 were AG genotypes. The genotype frequency and allele frequency of the pig (G\A) locus in the tested pig population are shown in Table 1:

[0063] Table 1. Genotype frequency and allele frequency of the pig (G\A) locus in the tested pig population

[0064]

[0065] As can be seen from Table 1, the genotype frequency of AG heterozygous type is significantly higher than that of GG homozygous type and AA homozygous type, and the G allele is the dominant gene.

[0066] 2. Correlation analysis between pig genotype and percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test

[0067] The anticoagulated blood of pigs was collected, and three-color fluorescent antibody staining was used to separate and identify cell subsets by flow cytometry, and the percentage of CD4-CD8+CD3+ mononuclear T cells was calculated. The measurement data are shown in Table 2.

[0068] Table 2: Genotype of (G\A) locus and percentage of CD4-CD8+CD3+ mononuclear T cells in routine blood of 489 Large White and Min pig F2 hybrid individuals

[0069]

[0070]

[0071] SAS software was used for the association analysis between genotype and phenotype, and Duncan's multiple test was used for significance test (P<0.05). The data were expressed as mean ± standard error, and P<0.05 was considered significant. The results are shown in Table 3. The SNP (G\A) site had a significant effect on the percentage of CD4-CD8+CD3+monocyte T cells in pig blood routine. The percentage of CD4-CD8+CD3+monocyte T cells in pig blood routine of GG genotype pigs was significantly higher than that of AG genotype pigs, and the percentage of CD4-CD8+CD3+monocyte T cells in pig blood routine of AG genotype pigs was higher than that of AA genotype pigs. Therefore, in actual pig breeding, GG genotype pigs have stronger immunity.

[0072] Table 3. Single nucleotide polymorphism at position 40842218 of chromosome 7 of pig and percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test

[0073]

[0074] Note: Different lowercase letters in the table indicate significant differences (P<0.05), the same letters indicate no significant differences (P>0.05), and the values ​​are mean ± standard error.

[0075] In summary, we determined the genotype of the (G\A) site at position 40842218 of chromosome 7 to assist in identifying the percentage of CD4-CD8+CD3+ monocytes in pig blood routine tests: the percentage of CD4-CD8+CD3+ monocytes in pig blood routine tests with the GG genotype was greater than that with the AG or AA genotype, and the percentage of CD4-CD8+CD3+ monocytes in pig blood routine tests with the AG genotype was greater than that with the AA genotype.

[0076] 3. A method for assisting in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test

[0077] The pig ear sample tissue to be tested was collected to extract genomic DNA, and the genomic DNA of the pig to be tested was used as a template, and PCR amplification was performed using the upstream primer: 5'-TGCTTTACTTCTGCCTTAGAGCAAT-3' and the downstream primer: 5'-TCCTCCTCTTGCCAACCCAC-3' to obtain a PCR product, and the PCR product was sequenced to obtain the genotype of the SNP (G\A) site of the pig to be tested.

[0078] The percentage of CD4-CD8+CD3+monocyte T cells in the blood of the pigs with genotype GG is greater than or more than that of the pigs with genotype AG or AA. The percentage of CD4-CD8+CD3+monocyte T cells in the blood of the pigs with genotype AG is greater than or more than that of the pigs with genotype AA.

[0079] Fourth, the present invention provides a SNP molecular marker that can effectively increase the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine. Using the SNP molecular marker for marker-assisted selection can accelerate the breeding process of related excellent traits. If all the AG genotype and AA genotype individuals of pigs are bred into GG individuals, the percentage of CD4-CD8+CD3+ mononuclear T cells in pigs will be improved. Among the SNP molecular marker individuals, the dominant allele GG of the SNP in the pig population can improve the pig's own immunity, thereby increasing the company's profits.

[0080] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be regarded as equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. Application of a reagent for detecting SNP sites related to the strength of pig immune system in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test, characterized in that: The SNP site corresponds to the 40842218bp of chromosome 7 of the international pig reference genome version 11.1, and is located in the CLIC5 gene; the polymorphism of the bases at this site affects the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests; The percentage of CD4-CD8+CD3+ mononuclear T cells in the blood routine test of the GG genotype pigs at the SNP site is higher than that of the AG genotype pigs and the AA genotype pigs; The percentage of CD4-CD8+CD3+ mononuclear T cells in the blood routine test of AG genotype pigs at the SNP site is higher than that of AA genotype pigs.

2. Use of a reagent for detecting SNP sites associated with the strength of the pig immune system in screening pigs with a high percentage of CD4-CD8+CD3+ mononuclear T cells in blood routine, characterized in that: The SNP site corresponds to the 40842218bp of chromosome 7 of the international pig reference genome version 11.1, and is located in the CLIC5 gene; the polymorphism of the bases at this site affects the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests; The percentage of CD4-CD8+CD3+ mononuclear T cells in the blood routine test of the GG genotype pigs at the SNP site is higher than that of the AG genotype pigs and the AA genotype pigs; The percentage of CD4-CD8+CD3+ mononuclear T cells in the blood routine test of AG genotype pigs at the SNP site is higher than that of AA genotype pigs.

3. Application of a reagent for detecting SNP sites related to the strength of pig immune system in genetic breeding for improving the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test, characterized in that: The SNP site corresponds to the 40842218bp of chromosome 7 of the international pig reference genome version 11.1, and is located in the CLIC5 gene; the polymorphism of the bases at this site affects the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine tests; The percentage of CD4-CD8+CD3+ mononuclear T cells in the blood routine test of the GG genotype pigs at the SNP site is higher than that of the AG genotype pigs and the AA genotype pigs; The percentage of CD4-CD8+CD3+ mononuclear T cells in the blood routine test of AG genotype pigs at the SNP site is higher than that of AA genotype pigs.

4. Application of a reagent for detecting SNP molecular markers related to the strength of pig immune system in identifying the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test, characterized in that: The nucleotide sequence of the SNP molecular marker is This SNP site is named (G\A) site, the nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AG or AA; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of GG genotype pigs is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of AG genotype pigs is higher than that of AA genotype pigs.

5. Use of a reagent for detecting SNP molecular markers related to the strength of the pig immune system in screening pigs with a high percentage of CD4-CD8+CD3+ mononuclear T cells in blood routine, characterized in that: The nucleotide sequence of the SNP molecular marker is This SNP site is named (G\A) site, the nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AG or AA; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of GG genotype pigs is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of AG genotype pigs is higher than that of AA genotype pigs.

6. Application of a reagent for detecting SNP molecular markers related to the strength of pig immune system in genetic breeding for improving the percentage of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test, characterized in that: The nucleotide sequence of the SNP molecular marker is This SNP site is named (G\A) site, the nucleotide type of the (G\A) site can be G or A, and the genotype can be GG, AG or AA; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of GG genotype pigs is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+monocyte T cells in the blood routine of AG genotype pigs is higher than that of AA genotype pigs.

7. A method for detecting the strength of a pig's immune system, characterized in that: The method comprises the following steps: detecting a SNP site of a pig located at 40842218bp of chromosome 7 of version 11.1 of the international pig reference genome and located in the CLIC5 gene; identifying whether the single nucleotide at the SNP site is A or G; determining the genotype of the tested pig; and analyzing and judging that the percentage content of CD4-CD8+CD3+monocyte T cells in the blood routine test of a GG genotype pig at the SNP site is higher than that of a AG genotype pig and a AA genotype pig; and the percentage content of CD4-CD8+CD3+monocyte T cells in the blood routine test of a AG genotype pig is higher than that of a AA genotype pig.

8. A primer composition for identifying SNP sites associated with the strength of the pig immune system, characterized in that: The primer composition comprises an upstream primer and a downstream primer, and the nucleotide sequence thereof is as follows: Upstream primer: 5′-TGCTTTACTTCTGCCTTAGAGCAAT-3′; Downstream primer: 5′-TCCTCCTCTTGCCAACCCAC-3′; The SNP site corresponds to the 40842218bp of chromosome 7 of the international pig reference genome version 11.1, and is located in the CLIC5 gene. The percentage of CD4-CD8+CD3+mononuclear T cells in the blood of GG genotype pigs at the SNP site is higher than that of AG genotype pigs and AA genotype pigs; the percentage of CD4-CD8+CD3+mononuclear T cells in the blood of AG genotype pigs is higher than that of AA genotype pigs.

9. Use of the primer combination as claimed in claim 8 in identifying the trait of the percentage content of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test.

10. Use of the primer combination as claimed in claim 8 in screening pigs with a trait of high percentage of CD4-CD8+CD3+ mononuclear T cells in routine blood tests.

11. Use of the primer combination as claimed in claim 8 in genetically assisted breeding for improving the percentage content of CD4-CD8+CD3+ mononuclear T cells in pig blood routine test.

12. A kit for identifying SNP sites associated with the strength of pig immune system, characterized in that: The kit comprises the primer combination according to claim 8.

13. The kit for identifying SNP sites associated with the strength of the pig immune system according to claim 12, characterized in that: The kit also includes at least one of a PCR reaction buffer, Taq DNA polymerase and dNTPs.

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