Review: The potential of seminal fluid mediated paternal–maternal communication to optimise pregnancy success

Artificial insemination has been a landmark procedure in improving animalagriculture over the past 150 years. The utility of artificial insemination hasfacilitated a rapid improvement in animal genetics across agricultural species,leading to improvements of growth, health and productivity in poultry, swine,equine and cattle species. The utility of artificial insemination, as with allassisted reproductive technologies side-steps thousands of years of evolutionthat has led to the development of physiological systems to ensure thetransmission of genetics from generation to generation. The perceivedmanipulation of these physiological systems as a consequence of assistedreproduction are points of interest in which research could potentially improvethe success of these technologies. Indeed, seminal fluid is either removed orsubstantially diluted when semen is prepared for artificial insemination indomestic species. Although seminal fluid is not a requirement for pregnancy,could the removal of seminal fluid from the ejaculate have negative consequenceson reproductive outcomes that could be improved to further the economic benefitof artificial insemination? One such potential influence of seminal fluid onreproduction stems from the question; how does the allogeneic foetus survivegestation in the face of the maternal immune system? Observation of the maternalimmune system during pregnancy has noted maternal immune tolerance topaternal-specific antigens; a mechanism by which the maternal immune systemtolerates specific paternal antigens expressed on the foetus. In species likehuman or rodent, implantation occurs days after fertilisation and as such themechanisms to establish antigen-specific tolerance must be initiated very earlyduring pregnancy. We and others propose that these mechanisms are initiated atthe time of insemination when paternal antigens are first introduced to thematernal immune system. It is unclear whether such mechanisms would also beinvolved in domestic species, such as cattle, where implantation occurs weekslater in gestation. A new paradigm detailing the importance ofpaternal–maternal communication at the time of insemination isbecoming evident as it relates to maternal tolerance to foetal antigen andultimately pregnancy success.