Breeding-induced endometritis is a physiologic inflammation which plays an important role on equine uterine clearance. However, when this inflammatory response persists, it becomes one of the most frequent causes of sub-fertility in mares. A healthy uterine milieu is necessary for fertilization and embryo development. Host defense peptides (HDP) could have an antimicrobial and anti-inflammatory role on cellular uterine immune response. The aim of this trial was to identify and quantify the presence of the 3 cathelicidins types (eCATH) in stallion seminal plasma. Semen samples were collected from 15 mature (aging 5 to 10 years), healthy and reproductively active Quarter Horse stallions by artificial vagina. Spermatozoa were separated from seminal plasma by centrifugation (800 x g) at room temperature for 10 min. The supernatant was further clarified using a 0.22µm filter. A protease inhibitor was added, following storage at -20°C until use. Protein concentrations were determined by a bicinchoninic acid protein assay kit. SDS-PAGE was performed in a vertical system using stacking and resolving gels containing 5% and 15% of polyacrylamide, respectively. Protein concentration was standardized to a total of 24µg per lane, allowing comparison of the respective protein densities among stallions. An equivalent amount of protein was loaded to build a dot-blotting test. On dot-blotting, three specific rabbit polyclonal antibodies were used to each peptide target. Total protein concentration among animals ranged from 6.27 to 25.65 mg/mL. On SDS-PAGE, bands with the same cathelicidin molecular weight were found. Dot-blotting revealed peptide concentrations among animals ranging from 9.7 to 339.6 ng of eCATH-1, 3.7 to 141.3 ng of eCATH-2 and 5.4 to 324.1ng of eCATH-3. Through the analysis of the obtained results, the presence of these peptides was confirmed. They seem to be involved inducing and modulating the inflammatory reaction beyond antimicrobial protection, being responsible for some cases of mare sub-fertility.