Comparative analysis of uterine inflammation in jennies and mares after insemination with cryopreserved donkey semen.

Overview

• This study compares uterine inflammation and pregnancy rates between jennies (female donkeys) and mares (female horses) following insemination with frozen donkey semen.
• Findings suggest jennies have a stronger, longer-lasting uterine inflammatory response that may explain their notably lower fertility compared to mares.

Background and Objective

• Artificial insemination (AI) using frozen donkey semen is a critical method for donkey reproduction and conservation.
• Jennies generally show poor fertility outcomes following AI with frozen semen, unlike mares that tend to have better reproductive success.
• The research aims to determine if differences in post-breeding uterine inflammation between species contribute to this disparity.

Study Design and Methods

• Subjects:
  • 12 jennies monitored over 48 estrous cycles
  • 11 mares monitored over 44 estrous cycles
• Timing & Procedure:
  • Artificial insemination was performed immediately after ovulation (time zero, T0).
  • Each insemination used 1 x 10 frozen-thawed donkey spermatozoa deposited deep into a uterine horn.
• Measurements taken at multiple time points (from T0 to T120 hours post-AI):
  • Ultrasonographic assessments: endometrial edema (EE), intrauterine fluid (IUF), and uterine vascular perfusion.
  • Blood serum tests: progesterone (P4) and acute-phase proteins (APPs) indicating systemic inflammation.
  • Endometrial cytology at T0, T6, T24, T48 to analyze cellular inflammatory response.
  • Uterine biopsies at T0, T12, T48 for histological examination including COX-2 expression.
  • Pregnancy diagnosis conducted on Day 14 post-AI.

Key Findings

• Endometrial Edema and Fluid Accumulation:
  • Jennies showed consistently lower levels of endometrial edema and intrauterine fluid than mares.
• Inflammatory Cell Response:
  • Both species showed peak neutrophil recruitment at 6 hours post-insemination.
  • Inflammation resolved within 48 hours in mares.
  • In jennies, inflammation persisted beyond 48 hours with a distinctive eosinophilic infiltration, which was absent in mares.
• Acute-Phase Proteins and COX-2 Expression:
  • No significant differences found between jennies and mares, suggesting similar systemic inflammatory responses at that level.
• Progesterone Levels:
  • Jennies had significantly higher serum progesterone concentrations on Day 5 post-ovulation (13 ng/mL) compared to mares (6 ng/mL).
• Pregnancy Outcomes:
  • Mares had a pregnancy rate of 54.55%.
  • Jennies had 0% pregnancy success under the same conditions.

Interpretation and Implications

• The strong and prolonged uterine inflammation in jennies, especially marked by eosinophil presence, likely contributes to their poor fertility outcomes after AI with frozen donkey semen.
• Lower ultrasonographic markers like edema and fluid in jennies suggest a different pattern of uterine response despite the intense inflammation.
• Similarities in acute-phase proteins and COX-2 expression indicate that systemic and some molecular inflammatory pathways are comparable between species.
• Higher progesterone in jennies could influence uterine environment and immune responses, possibly exacerbating inflammation or affecting embryo survival.
• This species-specific uterine immune response highlights the need for tailored reproductive management and therapeutic interventions in donkeys to improve AI success and conservation efforts.

Conclusion

• Jennies and mares respond differently to frozen donkey semen with respect to uterine inflammation and fertility outcomes.
• Prolonged and eosinophil-rich inflammation in jennies may create a hostile environment for pregnancy establishment.
• Developing targeted strategies to modulate uterine inflammation in jennies could enhance fertility and support preservation of donkey populations.