Association of Single-Nucleotide Polymorphisms of MDR1 and OPN Genes with Reproductive Traits in Different Breeds of Sows

Yifan Ni1, Jian Liu1, Fen Wu1, Jianfeng Cai1, Jinzhi Zhang1*, Jianqing Hua2 and Jiping Fu2

1College of Animal Science, Zhejiang University, Hangzhou 310058, China

2Zhejiang Jiahua Pig Breeding Company Limited, Jinhua 321053, China

ABSTRACT

The objective of this study was to investigate the single-nucleotide polymorphisms (SNP) of the Multiple Drug Resistance Gene 1(MDR1) and the Porcine Osteopotin (OPN) gene and their association with reproductive traits in Landrace, Large Yorkshire and Jinhua sows. A total of 316 sows of three different breeds were used to examine the genotypes, and DNA sequencing method was employed to detect the potential SNPs in this study. There were two SNP loci found in these genes totally. One mutation (G→A) was detected in exon 1 of MDR1 gene, which caused a synonymous mutation of amino acid (Leu→Leu), the other one (T→A) in exon 7 of OPN gene, resulting in a non-synonymous mutation (His→Gln). The association analysis indicated that the GG genotype of MDR1 gene and the TT genotype of OPN gene had the highest values for the total number of piglets born (TNB), the number of piglets born alive (NBA), piglet weight at birth (PWB) and litter weight at birth (LWB) in both primiparous and multiparous sows of the three breeds. These results suggested that the SNP locis of MDR1 and OPN genes can be used in Marker-Assisted Selection (MAS) programs for rapid improvement of the reproductive traits in sows.

Article Information

Received 22 August 2019

Revised 13 October 2019

Accepted 30 October 2019

Available online 28 January 2021

Authors’ Contribution

JL and FW conceived and designed the experiments. YFN and JFC performed the experiments. JQH and JPF analyzed the data. JL and JFC contributed reagents/materials/analysis tools. YFN and FW contributed to the writing of the manuscript. JZZ revised the manuscript.

Key words

MDR1, OPN, Single-nucleotide Polymorphism, Reproductive traits, Sows

DOI: https://dx.doi.org/10.17582/journal.pjz/20190822030826

* Corresponding author: [email protected]

0030-9923/2021/0002-0493 $ 9.00/0

Copyright 2021 Zoological Society of Pakistan

INTRODUCTION

Reproductive traits, especially litter traits, are one of the most economically important parameters in pig production (Linville et al., 2001). As the same time, reproductive traits are highly complicated, however, with rather low heritability which is only about 0.1, among various characteristics (Johnson et al., 1999; Campbell et al., 2003). It is not obviously effective to apply conventional breeding methods to improve these traits. With the development of molecular biology, it has become possible to find genetic markers and to carry out marker-assisted selection (MAS).

The human Multiple drug resistance gene 1(MDR1) is located on the long arm of chromosome 7 andcontains 28 introns (Pauli-Magnus et al., 2004), while the pig MDR1 is located on chromosome 9. The length of the MDR1 is 4.7 kb, less than 5% of the entire genome, encoding P-glycoprotein (P-gp) weighed 40 ku which consisting of 1280 amino acids in total. The P-gp is an ATP-dependent transmembrane outward transporter protein which can actively pump out chemical substances and drugs that are passively diffused into cells, leading to multiple drug resistance (Brambila-Tapia, 2013). As early as 1989, P-gp was reported to exist in tissues known to have blood-tissue barriers, such as the placenta (protecting the fetus), ovaries and testes, which were associated with reproduction (Sugawara et al., 1988; Cordon-Cardo et al., 1989). Later, Lankas et al. (1998) had found the importance of placental P-gp in protecting the fetus from potential teratogens, and the results showed that the fetus was more sensitive to teratogenic substances in pregnant mice lacking the MDR1 transporter in the placenta. There was confirmed that multiple drug resistant gene1 was closely related to treatments of many human diseases (Obata et al., 2006; Pauli-Magnus et al., 2004). Pappas et al. (2014) had also found that MDR1 gene expressed in placenta of human and guinea pig. However, the information on the association between polymorphism of MDR1 gene and reproductive traits of sows is poorly unknown. Based on the relationship between the MDR1 gene and the reproductive system diseases such as ovarian cancer (Obata et al., 2006) discussed above, we can speculate that the MDR1 gene may be closely related to animal reproductive organs and the polymorphism may be related to animal reproductive performance.

There was found that the porcine osteopotin gene (OPN) could increase the mRNA and protein expression of P-gp in a concentration- and time-dependent manner, and their results indicated that OPN was a potential therapeutic target for cancer therapy to reduce drug resistance in sensitive tumors (Hsieh et al., 2013). The osteopontin is a secreted glycosylation protein isolated from bone matrix by Bernards et al. (2008) which is rich in arginine-glycine-aspartate (Arg-Gly-Asp, RGD) structures. It plays an important role in mediating the connection between bone matrix and bone tissue cells and that’s why it’s called osteopontin. The binding of osteopontin and CD44 receptor plays a vital role in mediating the interaction between cell matrix and cell signal transduction (Stier et al., 2005). Meanwhile, osteopontin was also found to be involved in regulating embryonic growth and development, initiating and maintaining pregnancy (Garlow et al., 2002; Goncalves et al., 2007; Monaco et al., 2009). There are also an increasing number of studies showing that the Porcine Osteopontin (OPN gene) is expressed in humans and other mammals. It has been found that osteopontin expressed in various tissues such as bone, liver, testis, ovary and placenta (Pines et al., 1995). OPN gene, expressed abundantly in uterine epithelium and immune cells that were key contributors in pig embryo attachment and placentation, may interact with receptors and uterus to improve conceptus development and be the signaling between these tissues (Garlow et al., 2002). OPN mRNA expression in the ovine uterus was induced by progesterone and led to the secretion of OPN gene into the uterine lumen by endometrial glandular epithelium (Johnson et al., 2000). Given that OPN gene was detected in the uterus of humans, as well as pigs, Johnson et al. (2003) believed that the OPN gene had the potential to profoundly impact pregnancy. It has also been reported that the OPN gene expressed in both mature and immature oocytes and follicular cells (Monaco et al., 2008). Moreover, Kapelański et al. (2013) found the marker genotypes characterized by OPN gene had an important influence on the weight of the uterus, the weight and volume of the ovary and other reproductive system indicators in both breeds (Polish Large White and Polish Landrace gilts). However, while the studies on OPN gene polymorphism and porcine fertility is available in artificial insemination boars (Lin et al., 2006), Tibet pigs (Niu et al., 2008), Polish Landrace and Polish Large White sows (Korwin-Kossakowska et al., 2013) and other pig breeds, the literatures concerning OPN gene and prolificacy of Landrace, Yorkshire and Jinhua sows were limited. And we guess that the SNP of the OPN gene may be closely associated with reproductive traits of these sows through the above summary.

In this study, three sow breeds including Landrace, Large Yorkshire and Jinhua sows were selected as the research objects. Direct sequencing of DNA was applied to detect SNPs in exon 1 of MDR1 gene and exon 7 of OPN gene, we analyzed the associations between the SNP sites of MDR1 and OPN genes, and productive traits such as total litter size, alive litter size and litter weight at birth in both primiparous and multiparous sows. The goal of the study was to provide useful information for marker-assisted breeding to improve reproductive performance of sows.

 

MATERIALS AND METHODS

Ethics statement

All procedures involving animals were conducted in accordance with Chinese guidelines for animal welfare and approved by t the Laboratory Animal Center of Zhejiang University (Hangzhou, China).

Animals and DNA extraction

In the present experiment, ear tissue samples were collected from 316 sows, including 70 Landrace (18 primiparous sows and 52 multiparous sows), 140 Large Yorkshire (21 primiparous sows and 119 multiparous sows) and 106 Jinhua (17 primiparous sows and 89 multiparous sows), all from Zhejiang Jiahua Breeding Company Limited. All of these sows were provided same feed and water and kept under natural temperature conditions. The reproductive performance records of corresponding sows from 2011 to 2015 were analyzed and sorted out, including the total number of piglets born (TNB), the number of piglets born alive (NBA), piglet weight at birth (PWB) and litter weight at birth (LWB). 150 mg of pig ear tissue was cut into an EP tube, and DNA was extracted according to the instructions of the Tiangen Genoic DNA Extraction Kit. The extracted DNA was detected by 1.0% electrophoresis agarose gels, the DNA concentration was measured by Nano 2000 and diluted to 50ng L-1, and then stored them at 20°C for subsequent experiments.

Primer design and PCR amplification

In this experiment, primer sequences based on the pig MDR1 (GenBank NO. NC_010451.4) and OPN gene (GenBank NO. NC_010450.4) were designed by Primer 5.0 and synthesized by Invitrogen (Shanghai) Trading Company Limited. Taking the polymerase chain reaction (PCR) procedure into account, the primer sequences for MDR1 were as followings: forward 5’-GCGGTCTGGCTGATTGGC-3’ and reverse 5’-CCTCGGGCTTTCCCTCTG-3’; and the following were those for OPN gene: forward 5’-TGGATGCCACAGAGGAAG-3’ and reverse 5’-CATTCGAGATATTTTATTCACA-3’. The PCR was performed in a reaction volume of 25 μL containing 12.5 μL 2×Taq Master Mix, 1μL of forward and reverse primer respectively, 2 μL DNA template and 8.5 μL ddH2O. PCR amplification was performed using the following conditions: initial denaturation at 94°C for 5 min, 35 amplification cycles including denaturation at 94°C for 30 s, annealing at 55°C for 30 s, extension at 72°C for 1 min, and final extension at 72°C for 4 min. The PCR amplification products were examined by electrophoresis on 1.0% agarose gel.

PCR product purification and sequencing

The PCR products were sent to Shanghai Shenggong Biotechnology Company Limited for purification and sequencing. Sequencing peak maps and sequences were analyzed using BioEdit and DNA star software.

Statistics analysis

Allele frequency, genotype frequency, χ2 Hardy-Weinberg equilibrium estimations, polymorphism information content (PIC), population heterozygosity (He) and effective allele number (Ne) were calculated using POPGENE1.31. According to fixed effect model, General Linear Model (GLM) procedure in SAS 8.2 software was used to compare the reproductive performance of the four sow breeds among different genotypes of the 2 genes respectively. The following was the statistical models used in the analysis: Yijk=μ+Gi+Pj+Sk+eijk. Where Yijk is observation of reproductive traits; μ is the population mean; Gj is effect of gene; Pi is effect of parity (j=1, 2, 3…8); Sk is environmental effect (k=1, 2, 3, 4); and eijk is random error.

 

RESULTS

PCR amplification of MDR1 and OPN genes

Taking genomic DNA of different pig breeds as templates, the gene fragments of exon 1 of MDR1 gene and exon 7 of OPN gene were amplified, and the amplified products were detected by electrophoresis on 1.0% agarose gel. The amplified fragments were 280 bp and 780 bp, respectively (Figs. 1, 2), which can be used for subsequent studies because of the consistence with the expected fragment sizes, better amplification effects, better banding specificity, and higher brightness. The positions of amplified fragments on chromosome 9 of MDR1 and chromosome 8 of the OPN gene were from 93050045 to 93050281 and from 131077789 to 131078590 in accordance with Sscrofa11.1, respectively.

SNPs identification of MDR1 and OPN genes and its genotyping

The peak maps and sequences obtained after purification and sequencing of the PCR products were compared and analyzed by software such as BioEdit and DNA star (Figs. 3, 4). In the examined population of the three sow breeds, exon 1 of MDR1 gene was mutated at 154 bp (G→A), thus, leading to appearance of the three genotypes, namely, GG, AA and AG. There was no amino acid change at the location, which caused a synonymous mutation (Leu→Leu) (Fig. 3). For OPN gene, one mutation was detected in exon 7 of which at position 288, and the two alleles (T and A) with three genotypes (TT, AA, and AT) were determined (Fig. 4). Mutations at this site was a nonsynonymous mutation (His→Gln).

 

 

 

 

Genotypes and allele frequency of MDR1 and OPN genes and sample genetic characteristics

In Landrace, Large Yorkshire, and Jinhua sows, the major alleles of MDR1 and OPN genes were G and T, respectively. The allelic frequencies of MDR1 and OPN genes of the three population were shown in the Tables I and II. It could be seen from Chi-square test that MDR1 and OPN genes reached the Hardy-Weinberg equilibrium in all four populations (p>0.05). By analyzing the PIC, He and Ne of MDR1 and OPN genes in the three populations, it could be found that the PIC of MDR1 and OPN genes were more than 0.25 and less than 0.5 in the populations, indicating that MDR1 and OPN genes were in a moderate polymorphism in the study.

Association analysis of genetic polymorphism with reproductive performance

According to the two gene mutations for individual genotype, the least squares method was used to analyze the effects of different genotypes on traits (TNB, NBA, PWB and LWB) of the primiparous and multiparous sows of the three breeds in this experiment. From Tables III and IV, both MDR1 and OPN genes had significant effects on reproductive traits of the three sow breeds (P<0.05). Interestingly, in the primiparous and multiparous Landrace, Large Yorkshire and Jinhua sows, the reproductive traits (TNB, NBA, PWB and LWB) of the different genotypes of MDR1 gene all showed a trend of AA>GG>AG. The primiparous and multiparous sows with GG genotype had higher TNB, NBA, PWB and LWB values than AA genotype (P<0.05), although the AG genotypes were not significantly different from the GG and AA genotypes (P>0.05). The OPN gene also showed a similar trend that the TNB, NBA, PBW and LWB values of the TT genotype individuals were significantly higher than those of the AA genotype individuals (P<0.05); the difference between AT genotype individuals and TT genotype individuals was not significant; and either of AT genotype individuals or AA genotype individuals (P>0.05).

 

Table I. Genotype and allele frequencies at each locus of MDR1 gene.

Breeds	No.	Genotype frequency			Allele frequency		χ2	PIC	He	Ne
		GG	AG	AA	G	A
Landrace	70	0.3857(27)	0.3571(25)	0.2571(18)	0.5643	0.4357	0.2760	0.4905	0.4917	1.9673
Large Yorkshire	140	0.4500(63)	0.3643(51)	0.1857(26)	0.6321	0.3679	3.1450	0.3569	0.4651	1.8695
Jinhua	106	0.4057(43)	0.2830(30)	0.3113(33)	0.5472	0.4528	1.2360	0.3727	0.4955	1.9821

 

χ20.05(2)=5.99. PIC, polymorphism information content; He, heterozygosity; Ne, effective number of alleles.

 

Table II. Genotype and allele frequencies at each locus of OPN gene.

Breeds	No.	Genotype frequency			Allele frequency		χ2	PIC	He	Ne
		TT	AT	AA	T	A
Landrace	70	0.4143(29)	0.4571(32)	0.1286(9)	0.6429	0.3571	3.4760	0.3537	0.4592	1.8491
Large yorkshire	140	0.4500(63)	0.2571(36)	0.2929(41)	0.5786	0.4214	3.8750	0.3687	0.4876	1.9516
Jinhua	106	0.3962(42)	0.2547(27)	0.3491(37)	0.5236	0.4764	3.0550	0.3606	0.4893	1.9581

 

χ20.05(2)=5.99. PIC, polymorphism information content; He, heterozygosity; Ne, effective number of alleles.

 

Table III. Reproductive traits in relation to MDR1 gene.

Breeds	Genotype	Primiparous sows				Multiparous sows
		TNB	NBA	PWB	LWB	TNB	NBA	PWB	LWB
Landrace	GG	13.45 ±0.21a	12.51 ±0.77a	1.71 ±0.27a	21.41 ± 0.23a	13.96 ± 0.35 a	13.21 ± 0.88a	1.78 ±0.28a	23.52 ±0.87a
	AG	13.09 ±0.42ab	12.11 ±0.38ab	1.62 ±0.08ab	19.62 ± 0.41 ab	13.52 ± 0.53 ab	12.73 ± 0.16ab	1.68 ±0.18ab	21.38 ±0.44ab
	AA	12.51 ±0.26b	11.37 ±0.24b	1.52 ±0.15b	17.28 ± 0.56b	13.05 ± 0.25b	11.99 ± 0.27b	1.58 ±0.16b	18.93 ±0.37b
Large Yorkshire	GG	11.51 ±0.21a	10.53 ±0.23a	1.47 ±0.28a	15.48 ± 0.24a	12.13 ± 0.14a	11.25 ± 0.26a	1.51 ±0.43a	16.97 ±0.18a
	AG	10.94 ±0.23ab	10.07 ±0.24ab	1.35 ±0.18ab	13.61 ± 0.25ab	11.58 ± 0.33ab	10.74 ± 0.31ab	1.41 ± 0.28ab	15.15 ±0.18ab
	AA	10.31 ±0.34b	9.42 ±0.33b	1.29 ±0.13b	12.17 ± 0.37b	10.89 ± 0.19b	10.13 ± 0.45b	1.31 ± 0.12b	13.28 ± 0.11b
Jinhua	GG	12.78 ±0.24a	12.01 ±0.31a	1.06 ±0.04a	12.74 ± 0.34a	13.49 ± 0.22a	12.68 ± 0.34a	1.08 ± 0.23a	13.82 ± 0.14a
	AG	12.15 ±0.33ab	11.28 ±0.29ab	0.91 ±0.02ab	10.27 ± 0.22ab	12.94 ± 0.22ab	12.27 ± 0.19ab	0.99 ± 0.06ab	12.18 ± 0.13ab
	AA	11.51 ±0.31b	10.79 ±0.36b	0.82 ±0.03b	8.85 ± 0.34b	12.15 ± 0.23b	11.71 ± 0.66b	0.88 ± 0.15b	10.31 ± 0.24b

 

For the same trait among the same group of sows, values with different letter superscripts in the same line mean significant difference (P<0.05); with the same or no letter superscripts in the same line mean no significant difference (P>0.05). TNB, total number of piglets born; NBA, number of piglets born alive; PWB, pig weight at birth; LWB, litter weight at birth.

 

Table IV. Reproductive traits in relation to OPN gene.

Breeds	Genotype	Primiparous sows				Multiparous sows
		TNB	NBA	PWB	LWB	TNB	NBA	PWB	LWB
Landrace	TT	13.54 ±0.23a	12.46 ±0.47a	1.70 ±0.17a	21.26 ±0.51a	14.11 ±0.35 a	13.31 ± 0.68a	1.75 ± 0.18a	23.31 ± 0.87a
	AT	13.06 ±0.32ab	12.09 ±0.36ab	1.61 ±0.07ab	19.51 ±0.85 ab	13.62 ±0.23 ab	12.77 ± 0.19ab	1.65 ±0.17ab	21.06 ± 0.44ab
	AA	12.61 ±0.26b	11.42 ±0.19b	1.51 ±0.17b	17.25 ±0.41b	13.09 ±0.24b	12.05 ±0.25b	1.56 ±0.15b	18.76 ± 0.37b
Large Yorkshire	TT	11.29 ±0.22a	10.34 ±0.14a	1.48 ±0.48a	15.31 ±0.25a	11.89 ±0.24a	11.03 ±0.27a	1.53 ±0.49a	16.88 ±0.15a
	AT	10.98 ±0.24ab	10.03 ±0.09ab	1.36 ±0.28ab	13.65 ±0.26ab	11.49 ±0.33ab	10.72 ±0.33ab	1.41 ±0.26ab	15.11 ±0.11ab
	AA	10.54 ±0.33b	9.75 ±0.32b	1.31 ±0.01b	12.76 ±0.38b	11.12 ±0.21b	10.41 ±0.43b	1.33 ±0.11b	13.85 ±0.41b
Jinhua	TT	12.59 ±0.14a	11.81 ±0.11a	1.05 ±0.11a	12.42 ±0.14a	13.57 ±0.21a	12.81 ±0.31a	1.11 ±0.21a	14.23 ±0.14a
	AT	12.01 ±0.23ab	11.08 ±0.19ab	0.96 ±0.05ab	10.65 ±0.34ab	12.72 ±0.62ab	12.03 ±0.13ab	1.01 ±0.06ab	12.13 ±0.13ab
	AA	11.27 ±0.21b	10.69 ±0.33b	0.87 ±0.12b	9.42 ±0.31b	12.05 ±0.23b	11.31 ±0.46b	0.91 ±0.15b	10.33 ±0.24b

 

For the same trait among the same group of sows, values with different letter superscripts in the same line mean significant difference (P<0.05); with the same or no letter superscripts in the same line mean no significant difference (P>0.05). TNB, total number of piglets born; NBA, number of piglets born alive; PWB, pig weight at birth; LWB, litter weight at birth.

 

DISCUSSION

The reproductive traits of sows, including TNB, NBA, PWB and LWB, are important economic characteristics in modern pig production. The reproductive performance affects the production efficiency and economic benefits of farms directly. However, the heritability of reproductive traits is extremely low, and it is occurred at a low efficiency and rate about improvement of these traits (Bidanel et al., 2008). Thus, it is meaningful to study the genes related to reproductive traits of pigs and reveal the genetic mechanism affecting the reproductive performance and the prolificacy of high-breeding pigs. At present, many reports on MDR1 gene polymorphisms are related to its relationship with genital diseases. Compared to Landrace, Yorkshire, Duroc and Jinhua sows, studies on OPN gene polymorphisms have mainly focused on ruminants, avian animals and other pigs. Therefore, this study analyzed MDR1 and OPN genes of the three sow breeds to investigate the polymorphisms of the two genes in the pig populations. In the present study, we found that the polymorphisms of MDR1 and OPN genes impacted reproductive traits of the sows and could be markers.

In the present study, the MDR1 gene was used as a candidate gene to explore the reproductive performance of sows. The results showed that one mutation (G→A) occurred at 154 bp of exon 1 of MDR1 gene; among the three genotypes presented (GG, AA, AG), the sows with GG genotype had higher values about reproductive traits. We found that the mutation in the MDR1 gene had the same effect on the reproductive performance of different sow populations selected in this study. Previous studies have shown that MDR1 gene widely expressed in the fetal placenta and played pivotal roles in protecting the fetus from insults of drugs and xenobiotics, which might explain why MDR1 gene could prevent drugs from reaching the litter through the placenta (Pappas et al., 2014; Han et al., 2018). In view of low immunity of litters, MDR1 gene played an important role in protecting litters if the drug reached the body of the dam and mighty cause the death of litters. This may explain that the MDR1 gene polymorphism has a significant effect on reproductive traits in sows. This is also consistent with our results, thus, these findings could suggest that MDR1 gene may be a candidate gene associated with sow reproductive performance and that the mutation site detected in this gene may be a useful genetic marker for reproductive performance in pigs.

The studies on OPN gene have become increasingly popular these years, and many of them are the ones on the polymorphisms at present. In pregnant sows, OPN gene was induced by conceptual estrogen in the uterine luminal epithelium and was regulated in the glandular epithelium in a manner consistent with placental progesterone production (White et al., 2005). Extracting the samples of the sow ovary and fallopian tube tissue, Goluch et al. (2009) detected two mutations (A→G) occurring at positions of 617 and 608, respectively. Nevertheless, it could be found that the major alleles and their frequencies of the OPN gene mutations varied from one study to the next. Lin et al. (2006) by investigating mutations in the OPN gene intron of the purebred Pitland boars, crossbred Hampshire Pietrain boars in northwestern Germany, found the frequencies of the B allele were 0.54 and 0.75, respectively. Niu et al. (2008) used the DNA mutation in the OPN gene to determine the associations between the genotype and litter size in Tibet pigs, and their data showed that B allele was dominant in Tibet pigs with a frequency of 0.804. Three different genotypes (AA, AB, BB) were found in the mutation of the intron 6 of the OPN gene in 71 sows (46 in the luteal and 25 in the follicular phase) in the Korwin-Kossakowska et al. (2013) ’s experiment, and the frequency of major allele B was 0.61. However, Oztabak et al. (2008) found that the OPN gene had a mutation (T→G) and the frequency of T allele was higher. And in our study, the mutation (T→A) occurred at 288 bp of exon 7 of OPN gene, which caused the frequencies of major alleles in the four populations were 0.64, 0.58 and 0.52, respectively. Many studies have found that the OPN gene was closely related to the reproductive traits of pigs. Southwood et al. (1998) suggested that it was possible to use the microsatellite sequence in the OPN gene locus as a marker of the reproductive traits TNB and NBA. They found 13 alleles, five of which were related to litter size in the synthetic line. And the polymorphism of OPN gene had a significant effect on boar fertility traits such as NBA (Lin et al., 2006). Meanwhile, previous studies by Zhang et al. (2010) showed that the genotype of AA and AB of OPN gene could increase the LWB, but did not reach the significant level. The expression level of the OPN gene was significantly associated with LWB (Korwin-Kossakowska et al., 2013). Among the mutation sites found in this study, three genotypes, TT, AA and AT, were detected, and TT was the dominant genotype. In the primiparous and multiparous sows of the 3 populations texted, the reproductive performance of the TT genotype was significantly better than the AA genotype (P<0.05). However, considering that the reproductive performance of livestock is affected by many factors, and the genetic background of different varieties is very different, the effects of each genotype on reproductive performance can be different. Therefore, it is also necessary to expand the sample size to conduct further systematic studies on different breeds of pigs.

 

CONCLUSIONS

In conclusion, our results found that polymorphisms of the MDR1 and OPN genes were associated with reproductive traits in Landrace, Large Yorkshire and Jinhua three sow breeds. The present study showed that sows with the GG genotype of MDR1 gene or the TT genotype of OPN gene had the highest values for reproductive traits (TNB, NBA, PBW and LBW) in both primiparous and multiparous sows of the 3 breeds. We indicate that MDR1 and OPN genes may be possible markers of reproduction traits. However, it is also necessary to conduct further systematic studies on other different breeds of pigs, as there may be different results for different breeds.

 

ACKNOWLEDGMENTS

This study was supported by National Key Research and Development Program of China (2016YFD0500503), the Program of Breeding of New Species of Agricultural (Livestock and Poultry) Program in Zhejiang (2012C12906-6) and (2016C02054-3).

 

Competing interests

All the authors declared no conflict of interests.

 

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