When boar semen is frozen and thawed (FT) the fertility rate of the insemination is lower than fresh semen; fewer sperm live at thawing and there is a shorter lifespan of surviving sperm in the female reproductive tract. This project looked at incubating thawed semen in seminal plasma (SP) to see how it effected sperm viability and mortality in virtro. Also how SP effected in vivo sow fertility to double conventional AI, or single intrauterine AI. For the in vitro test, FT sperm were thawed and incubated for 4 hours with either 0%, 10% or 50% SP. Sperm populations were examined for viability and mortality every hour they were incubated for. Incubation in 50% SP increased percentages of live sperm and sperm motility at all time points compared to incubation in either 0% or 10% SP. For the in vivo test 82 sows were used, sows received 3 x 109 live fresh-extended sperm or FT sperm thawed in 80 mL BTS extender or 3 x 109 live FT sperm thawed in 80 mL BTS containing 50% SP (FT-SP). Sows who received fresh semen had the highest pregnancy rate followed by the FT-SP group, the FT group having the lowest rate. Farrowing rates were not different. In the in vivo single intrauterine AI test, 97 sows were inseminated at 36 h after pLH with 3 x 109 live FT sperm with or without 50% SP, or 3 x 109 fresh sperm. Compared to controls, insemination of FT-SP decreased farrowing rate but litter sizes were not different from controls. These results confirm that there is an adverse effect of inseminating FT sperm on sow fertility but using sperm that has been incubated in 50% SP can partially alleviate these negative effects.