Sperm-induced leukocytosis in the equine uterus

The objective of this study was to investigate the inflammatory reaction induced in the equine uterus by insemination with fresh and frozen semen. Eleven groups (6 to 8 mares per group) were studied during 2 breeding seasons. The mares were inseminated using raw semen, frozen semen, extended fresh and frozen semen, concentrated fresh semen, seminal plasma and seminal extenders only. One group was bred naturally. Six hours after insemination, the uteri were flushed with 50 ml of phosphate-buffered saline (PBS). Seventeen out of 104 samples (16%) exhibited slight bacterial growth. Neutrophil concentrations were significantly (P<0.05) higher in all treated mares than in the controls. Mares infused with PBS, seminal extenders or the supernatant from centrifuged frozen-thawed semen exhibited only a mild neutrophil response. Insemination with frozen semen resulted in higher neutrophil concentrations than insemination with extended fresh semen (means of 59 vs 5 million neutrophils/ml; P<0.05). Highest neutrophil counts were found after insemination with frozen semen or concentrated fresh semen. Bacterial contamination of uteri was insignificant 6 hours after breeding. Neutrophilia seems to be induced by spermatozoa rather than bacteria. The intensity of the neutrophil reaction seems to depend on concentration and/or volume of inseminate.