Seasonal or pathological findings? Morphofunctional characteristics of the equine endometrium during the autumn and spring transition.

This research aims to understand the structural and functional characteristics of a mare’s endometrium during transitional periods in the fall and spring, to determine the best time for biopsy sampling. The findings suggest that endometrial activity is low from late October to early April, with a significant amount of irregular differentiation during these transitional periods.

Evaluating the Equine Endometrium

• The study focuses on characterizing the morphofunctional properties of the endometrium in female horses during the transitional periods of Autumn and Spring.
• These periods are around the deep anoestrous phase, a time of sexual inactivity or anovulatory season in mares.
• The objective was to define an accurate time window for effective prognostic biopsy sampling.

Methodology

• Endometrial samples were gathered in the months of September, October, and November, as well as February, March, and April, and were analyzed with a detailed clinical documentation.
• The histological examination placed special emphasis on the functional morphology of the endometrium.
• Certain specimens were selected for an immunohistochemical evaluation to study the expression of oestrogen receptor α, progesterone receptor, and the Ki67-antigen, a protein associated with cell proliferation.

Findings

• The study found that endometrial activity was absent or very low in over 60% of all specimens from late October till early April.
• About 30% and 22% of the samples during the Autumn and Spring transitional periods respectively exhibited predominantly ‘irregular’ differentiation.
• The ovarian status based on clinical evaluation, and the functional endometrial morphology was in accordance for approximately 70% of all cases.
• Expression of the steroid hormone receptors and the Ki67-antigen, generally, was low in the samples.

Implication

• The frequent occurrence of endometrial maldifferentiations during the transitional periods could be a typical and physiological characteristic of the transitional periods.
• Based on findings related to the functional morphology of the endometrium, a diagnostic biopsy sampling should ideally be performed between late April and prior to September.