Sperm-induced leukocytosis in the equine uterus.

This research study investigates the inflammatory reaction occurring in the uterus of horses after insemination with fresh and frozen semen. It concluded that insemination causes initial increase in neutrophils, a type of white blood cell, indicative of an inflammatory response and this seems to be caused more by sperm than bacteria, with the severity depending on the concentration and/or volume of semen used.

Objective and Methodology

• The goal of the study was to understand the inflammatory response caused in a horse’s uterus by insemination with fresh and frozen semen.
• In order to investigate this, the researchers studied eleven groups composed of 6 to 8 mares during two breeding seasons. Various types of semen were utilised in different groups, including 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 post insemination, the uteri of the mares were flushed with phosphate-buffered saline (PBS), a salt solution often used in medical research to balance pH and osmotic pressure.

Results and Findings

• Observations showed that 16% of the samples (17 out of 104) showed some bacterial growth.
• A significant increase in neutrophil concentrations, which are white blood cells aiding in combating infections, was observed in all mares that were treated in comparison to control mares.
• However, mares which were only administered PBS, seminal extenders or supernatant from frozen-thawed semen reflected a milder neutrophil response compared to others.
• The study found that insemination with frozen semen resulted in a larger increase in neutrophil count than insemination with extended fresh semen, with concentrations of 59 million versus 5 million neutrophils/ml respectively.
• The highest observed increase in neutrophil count came after insemination with either frozen semen or concentrated fresh semen.
• Bacterial contamination of the uterus was not found to be significant 6 hours post breeding.

Conclusion

• The study concludes that an increase in neutrophils, indicative of inflammation in the uterus, seems to be induced by spermatozoa and not primarily due to bacteria.
• The intensity of this neutrophil response or inflammation seems to be dependent on the concentration or volume of the semen used for insemination.