Role of Seminal Plasma in the Equine Reproduction

Seminal plasma (SP) has a very important role in the equine reproductive strategy. Physiologic endometritis occurs when the semen rises the uterus after a natural mating or an artificial insemination. A large amount of polymorphonuclear neutrophils (PMN) reaches the uterine lumen. These PMN will eliminate many sperm, selecting those that will advance to the fertilization site by means of the neutrophil extracellular traps (NETs) production. SP induces and controls the NETs production. The sperm metabolism produces an important amount of reactive oxygen species (ROS), but the NETosis produces much more, inducing endometrial oxidative stress. SP plasma is an important source of enzymatic and non-enzymatic antioxidants to protect the spermatozoa. SP metabolomics evidenced similar metabolites between horse and donkey semen; however, the amount and the role of each metabolite are different between species. The study of these metabolites is very important to improve sperm metabolism and to design extenders for both species. Recently, SP exosomes and microvesicles have been identified. These vesicles contain proteins and microRNAs whose role is still unknown.