Glutathione peroxidase-5 (GPX5) is an H2O2-scavenging enzyme identified in boar seminal plasma (SP). This study attempted to clarify its origin and role on sperm survival and fertility after artificial insemination (AI). GPX5 was expressed (Western blot and immunocytochemistry using a rabbit primary polyclonal antibody) in testes, epididymis and accessory sex glands (6 boars). SP-GPX5 concentration differed among boars (11 boars, P amp;lt; 0.001), among ejaculates within boar (44 ejaculates, P amp;lt; 0.001) and among portions within ejaculate (15 ejaculates). The first 10 mL of the spermrich fraction (SRF, sperm-peak portion) had a significantly lower concentration (8.87 +/- 0.78 ng/mL) than the rest of the SRF and the post-SRF (11.66 +/- 0.79 and 12.37 +/- 0.79 ng/mL, respectively, P amp;lt; 0.005). Spermmotility of liquid-stored semen AI-doses (n = 44, at 15-17 degrees C during 72h) declined faster in AI-doses with low concentrations of SP-GPX5 compared to those with high-levels. Boars (n = 11) with high SP-GPX5 showed higher farrowing rates and litter sizes than those with low SP-GPX5 (a total of 5,275 inseminated sows). In sum, GPX5 is widely expressed in the boar genital tract and its variable presence in SP shows a positive relationship with sperm quality and fertility outcomes of liquid-stored semen AI-doses.