Genetic group and swim-up processing affect SYBR Green real-time PCR-based porcine semen sex ratio in Landrace and its crossbred boars

Determination of factors affecting sex ratio is important while considering application of sex ratio enrichment approach. Present study aimed to design a SYBR Green qPCR-based method for measurement of primary sex ratio and to evaluate different factors (genetic group, sire, spermiogenic cycle and processing layer) affecting boar sperm sex ratio. The qPCR was based on relative copy number analysis of sex chromosome-specific single copy gene fragments with an autosomal gene as reference and was evaluated using DNA dilution series from pigs with numerically normal karyotype. The sex ratio was estimated from genomic DNA samples isolated from boar semen collected from different genetic groups at different time points and different processing layers. The X chromosome frequencies of semen samples revealed significant effect of genetic group. However, significant variation was observed neither within same genetic group nor between ejaculates of different spermatogenic cycles. Among the processing techniques studied, swim-up technique produced a significant X sperm enrichment in comparison to control whereas, Percoll density gradient failed to show any significant difference among layers. The lower layer in swim-up technique was found to contain higher proportion of X sperms. The designed qPCR is found to be an easy, less time-consuming method and does not require high end laboratory facilities or the specialized expertise. The lower layer of swim-up processing has a scope for X sperm enrichment in boar semen with proper validation.