Genotype frequencies
Genotypes frequencies of the tested SNP in
ESR,
FSHB and
PRLR are shown in Table 3. For
ESR gene, the frequency of AA genotype was high (0.81) in Landrace while it was very low (0.02) in Yorkshire. The BB genotype in
FSHB gene was not found for Yorkshire boars. Three genotypes of
PLRL were observed in both breed with AA frequencies of 0.48 and 0.25 for Landrace and Yorkshire respectively. The genotype frequencies of
ESR,
FSHB and
PRLR were in Hardy-Weinberg equilibrium for each breed (P>0.160).
Effects of genotype on sperm traits
The effects of genotypes, breed, age and months of the years on sperm traits are shown in Table 4. VOL was significantly different between
ESR (P=0.0259) and
FSHB SNP genotypes (P=0.0321). An effect of
FSHB and
PRLR SNP on MO was found (P<0.0045). Only
FSHB SNP affected CO (P=0.0318). Age of boars and month of the year significantly affected all sperm traits (P<0.0001) except CO (P=0.0661) while breed did not affect any trait (P>0.8524).
The effects of
ESR genotypes on sperm traits are shown in Table 5. Boars with AA and AB genotypes had a significantly higher VOL than those with BB genotype (P=0.0259). There was no significant difference for MO, CO and NT among
ESR genotypes.
The results in Table 6 show that
FSHB genotype was significantly associated with VOL, MO and CO. Boars with BB genotype showed positive effect on VOL, in comparison with AA boars (P=0.0321). In contrast, AA genotype leaded to higher MO and CO than BB genotype (P<0.0318). Heterozygote AB leaded to intermediate results for both parameters. No significant effect of FSHB genotype on NT was observed in this study (P=0.6555).
The
PRLR genotype only significantly affected MO (Table 7). The boars with AB genotype showed higher MO than those with AA genotype (P=0.0044). No significant difference for
PRLR genotypes was observed for VOL, CO and NT (P>0.3699).
Genotype frequencies
From literature review, the used
ESR,
FSHB and
PRLR SNP were shown to have three genotypes (AA, AB and BB) with varying frequencies in different swine populations. Most of the previous studies reported the predominance AA genotype for
ESRS NP, in comparison with AB and BB genotypes (
Terman and Kumalska 2012,
Vega et al., 2018). For
FSHB SNP, the predominant genotype seemed to be BB in Large White and Landrace pigs. For the
PRLR gene SNP, AA genotype showed higher frequency than the others in several reports (
Huang et al., 2006,
Barreras-Serrano et al., 2009).
For
ESR, BB genotype in Yorkshire (0.52) was higher than in Landrace (0.03) boars. In contrast, a very low frequency of AA genotype was observed in Yorkshire while it was very high in Landrace in current study.
Terman et al., (2006) found a high frequency (0.83) of allele A in boar of seven different breeds. While boar with BB genotype was not observed in Piétrain and Hampshire × Piétrain.
Zinnatova et al., (2014) found only heterozygote AB in the Landrace and Large White boars.
The AA genotype of the
FSHB gene was more frequent than BB genotype in both breeds. In particularly, there was not any Yorkshire boars with BB genotype observed in the present study. A research by
Lin et al., (2006) revealed that allele A showed a high frequency in Piétrain (0.83) and the Piétrain × Hampshire (0.82) boars. Similarly,
Korwin-Kossakowska et al., (2003) reported allele A frequencies of more than 0.90 in a synthetic pig line, which was selected for reproductive traits. In contrast, studies of
Kapelański et al., (2013) and
Polasik et al., (2016) showed that BB genotype in Landrace gilts was predominant. In the last two study, the frequency of BB was more than 0.82.
In our study, the allele A of the
PRLR SNP was more frequent than allele B in both breeds. This result is in agreement with findings in the Duroc and Landrace boars (
Huang et al., 2006). The effect of selection, different allelic frequencies in the founder animals and random genetic drift could have caused allele frequencies to differ among lines (
Linville et al., 2001).
Effects of genotype on sperm traits
In the present study, the
ESR gene SNP was proven to significantly (P<0.05) affect only ejaculate volume in boars. VOL of the boars carrying allele A was higher than those carrying allele B. This finding is not in agreement with the report of
Terman et al., (2006) where VOL was not significantly different between boars carrying alleles A and B. Additionally, the authors also found the effect of
ESR genotypes on CO, sperm alive percentage and number of alive sperm. The total number spermatozoa were significantly higher in BB boars compared to AA and AB genotypes in Danube white pigs (
Stoyanova et al., 2010) and in Large White pigs (
Kostenko and Sydorenko, 2011).
The polymorphism of the
FSHB locus was significantly associated with VOL, MO and CO of the boars. Boars with BB genotype showed the highest ejaculate VOL and the lowest CO and MO values. In contrast, AA genotype was associated with the lowest ejaculate VOL but with the highest CO and MO. Inversely,
Lin et al., (2006) did not find any association between
FSHB and sperm traits in Piétrain and Piétrain × Hampshire boars.
Ford et al., (1997) reported a negative relationship in mature Meishan boars between
FSH secretion and testicular size accompanied with decreased total daily sperm production;
FSH affected spermatogenesis (
Zanella et al., 1999). The functional association evidence of the
FSHB gene arises from knockout experiments showing that deficiency at the
FSHB gene leads to decrease sperm concentration to 75% in mice (
Layman, 2000).
In current study,
PRLR gene significantly affected sperm motility of the Landrace and Yorkshire boars. MO of boars with AA genotype was lower than those with AB. This result was not consistent with report of
Huang et al., (2006) that Duroc boars with the AA genotype had significantly better semen quality, which higher VOL (P<0.05) and MO tended to be higher than those with the AB genotype (P<0.1). In contrast, no significant effect of the
PRLR locus was observed on any semen trait of the Piétrain and the Piétrain × Hampshire crossbred population (
Lin et al., 2006). These results indicate that effect of
PRLR depends on the different breeds.
