Reproductive traits play a key role in pig production in order to reduce costs and increase economic returns. Among others, gene expression analyses represent a useful approach to study genetic mechanisms underlying reproductive traits in pigs. The application of reverse-transcription quantitative PCR requires the selection of appropriate reference genes, whose expression levels should not be affected by the experimental conditions, especially when comparing gene expression across different physiological stages.This study was funded by the Spanish Ministerio de Ciencia e Innovación (grant AGL2004-08368-C03/GAN). RN Pena received a contractual grant from INIA. M Martínez-Giner received a predoctoral fellowship from MICINN. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript