Uterine defence mechanisms in mares resistant and susceptible to persistent endometritis: a review.

The article reviews the different defense mechanisms in mares, wherein some are susceptible to persistent endometritis while others are resistant. Specifically, the paper aims to better understand why high rates of unsuccessful pregnancy attempts persist in intensively bred mares and how this could be linked to the condition known as persistent endometritis, a chronic inflammatory issue within the uterus.

Introduction

• The research focuses on the condition of persistent endometritis in mares and its impact on their fertility. It notes that mares bred intensively often exhibit disappointingly low fertility levels. This is especially true in the cases of older, multiparous mares.
• The paper explores the physiological response of mares to persistent endometritis. It is proposed that some mares develop an immunological deficiency preventing them from resolving bacterial infections triggered in the uterus at the time of coitus.

Endometritis and Susceptibility

• The study further delves into the distinction between ‘susceptible’ mares and ‘resistant’ mares. Susceptible mares are unable to eliminate intra-uterine bacterial infections even within 72 hours of inoculation, leading to a persistent state of infection.
• The paper also examines the role of conformational characteristics, such as the shape and angulation of the vulva, in predisposing certain mares to persistent endometritis. It is mentioned that these traits are more common in larger breeds and can lead to pneumovagina, which subsequently results in inflammation and infection.

Diagnosis and Confirmatory Tests

• Methods of diagnosis for endometritis detailed in the paper include palpation, vaginoscopic examination, and the detection of neutrophils in endometrial smears. Additionally, the isolation of pathogenic bacterial growth from a uterine swab or wash contributes to a positive diagnosis.
• Confirmation of diagnosis involves microscopic examination of endometrial biopsy samples to further identify the presence of inflammation or infection. Key signs of persistent endometritis include infiltration of mononuclear cells and signs of degeneration in the glandular structures of the uterus.

Implications for Fertility

• The implications for fertility are also described in the article, wherein endometritis is linked to a significant drop in foaling rates. This decrease in fertility is often associated with changes within the uterus, such as cytotoxicity caused by neutrophil secretions, which are detrimental to both gametes and embryos.
• The study surmises that endometritis, which persists beyond the fifth day after ovulation, may initiate luteolysis and trigger loss of luteal support for pregnancy maintenance.