Relationship between the duration of endometrial edema and reproductive parameters of estrus, diestrus, and fertility in mares: a field study.

Overview

• This study investigated how the length of time mares show endometrial edema (swelling in the lining of the uterus) relates to various reproductive factors including follicle size, hormone levels, uterine characteristics, and fertility outcomes.
• The researchers found that a longer duration of endometrial edema was linked to better reproductive indicators and higher pregnancy rates in mares.

Research Purpose

• To examine if the duration of endometrial edema (DEdema) during the estrous cycle correlates with:
• Maximum endometrial edema (MEdema)
• Largest pre-ovulatory follicle diameter (LPF)
• Corpus luteum size and uterine tone on day 5 after ovulation (CLD5 and TD5)
• Progesterone hormone concentration (P4)
• Overall fertility and pregnancy rates

Study Design and Methods

• Subjects: 36 mares monitored over 88 estrous cycles in a field setting.
• Grouping of cycles:
• Short Estrus (SE) group: mares with brief estrus cycles (30.7% of cycles)
• Long Estrus (LE) group: mares with longer estrus cycles (69.3% of cycles)
• Within the inseminated group (AI), mares were further categorized as pregnant (P) or non-pregnant (N)
• Data collection:
• Monitored daily after dominant follicle and minimum uterine edema detection until ovulation (day 0)
• Measurements taken: dominant follicle diameter (LPF), endometrial edema score, corpus luteum size and uterine tone on day 5 after ovulation (CLD5, TD5), blood progesterone (P4) levels

Key Findings

• Duration of endometrial edema (DEdema) showed positive correlations with:
• Largest follicle diameter (LPF) – stronger follicles linked to longer edema (P = 0.001, r = 0.32)
• Maximum endometrial edema reached (MEdema) (P = 0.002, r = 0.31)
• Uterine tone on day 5 post-ovulation (TD5) (P = 0.01, r = 0.28)
• Fertility outcomes:
• Mares with longer DEdema had a higher likelihood of becoming pregnant (Odds Ratio 1.45; P=0.049)
• Pregnancy rates were significantly higher in the Long Estrus group (67.5%) compared to the Short Estrus group (16.6%) (P=0.006)

Conclusions and Implications

• Duration of endometrial edema is an important indicator of reproductive health in mares, reflecting:
• Better follicular development
• Stronger uterine tone compatible with successful pregnancy
• Higher progesterone levels supporting maintenance of pregnancy
• Monitoring endometrial edema duration can be a useful tool for predicting fertility and optimizing breeding management in mares.
• Extended estrus length characterized by prolonged edema is positively associated with greater fertility success.