Effects of Intrauterine Devices in Mares: A Histomorphological and Immunohistochemical Evaluation of the Endometrium.

This study explores the biological mechanisms beneath the prolonged luteal function that occurs when intrauterine devices (IUDs) are used in mares. Researchers found that mares with IUDs showed higher levels of certain uterine proteins and less expression of estrogen and progesterone receptors, and that younger mares with healthier blood vessels may experience more effective suppression of oestrus through the use of IUDs.

Research Methodology

• The study used a set of 30 mares, intentionally matched in age, and subjected them to different treatments – artificial insemination (AI) or IUD implantation (IUD). These mares were later categorized into four groups based on their reproductive status: AI-P (Artificially inseminated – pregnant, n=8), AI-N (Artificially inseminated – non-pregnant, n=7), IUD-P (IUD implanted – prolonged luteal phase, n=7), and IUD-N (IUD implanted – normal luteal phase, n=8).
• To understand the effects of both treatments, the researchers took endometrial biopsy samples on Day 15 after ovulation. These samples were used to study the histomorphology and immunohistochemical expression of various markers.

Research Results

• The research found that the IUD mares had a significantly higher expression of the uterine protein, Uteroferrin (UF), particularly when compared to the pregnant mares.
• Interestingly, mares that had a prolonged luteal phase, whether due to Artificial Insemination (AI-P) or IUD (IUD-P), showed lower levels of estrogen (ER) and progesterone receptors (PR) when compared to those with a normal luteal phase (AI-N, IUD-N). This hints at the possible link in the hormonal pathways that might be altered due to IUDs.
• No notable differences were observed in the numbers of inflammatory cells between the categories, except for the population of macrophages which were found to be more in AI-P mares than AI-N mares. This suggests only minor inflammatory responses due to IUDs.
• Despite the absence of evident inflammatory cells in IUD mares, the raised UF levels could be indicative of chronic inflammation.
• Lastly, the study also observed a correlation between the age of the mare and the condition of endometrial blood vessels to the efficacy of IUDs. It was hinted that younger mares with better vascular health may experience more effective use of IUDs.

Research Conclusions

• The study’s conclusions pointed towards IUDs’ effects on a biological level, asserting that histomorphological and immunohistochemical patterns could provide explanations for the observed prolonged luteal function in mares with IUDs. The mares showed an increased expression of uterine protein and a lower expression of oestrogen and progesterone receptors.
• However, the study stopped short of establishing a direct causal relationship between these phenomena, requiring future studies for establishing a concrete linkage.
• Also intriguing are the findings regarding younger mares and blood vessel health, giving useful clues to optimize the use of IUDs for oestrus suppression in the future.