Abstract
Post-breeding endometritis (i.e., inflammation/infection of the endometrium), is a physiological reaction taking place in the endometrium of mares within 48 h post-breeding, aimed to clear seminal plasma, excess sperm, microorganisms, and debris from the uterine lumen in preparation for the arrival of an embryo. Mares are classified as susceptible or resistant to persistent breeding-induced endometritis (PBIE) based on their ability to clear this inflammation/infection by 48 h post-breeding. Mares susceptible to PBIE, or those with difficulty clearing infection/inflammation, have a deficient immune response and compromised physical mechanisms of defense against infection. Molecular pathways of the innate immune response known to be involved in PBIE are discussed herein. The role of the adaptive uterine immune response on PBIE remains to be elucidated in horses. Advances in the pathobiology of microbes involved in PBIE are also revised here. Traditional and non-traditional therapeutic modalities for endometritis are contrasted and described in the context of clinical and molecular aspects. In recent years, the lack of efficacy of traditional therapeutic modalities, alongside the ever-increasing incidence of antibiotic-resistant microorganisms, has enforced the development of non-traditional therapies. Novel biological products capable of modulating the endometrial inflammatory response are also discussed here as part of the non-traditional therapies for endometritis.
Highlights
Endometritis, infection and/or inflammation of the endometrium, is the number one cause of subfertility and the third most common disease affecting horses [1,2]
The administration of recombinant lactoferrin at the time of breeding in the normal mare has shown varying results, with one study finding no change in cytokine expression [308], while another found a significant decrease in endometrial interleukin 6 (IL6), alongside a trend towards a decrease in CXCL8, interleukin 1β (IL1β), and TNFα [309], indicating its anti-inflammatory properties
For the treatment of endometritis in the horse, one study found that Platelet-rich plasma (PRP) administration at the time of breeding decreased the intrauterine inflammatory response in mares suffering from chronic endometritis, it did not affect nitric oxide (NO) production [332]
Summary
Endometritis, infection and/or inflammation of the endometrium, is the number one cause of subfertility and the third most common disease affecting horses [1,2]. Mares are classified as susceptible or resistant to persistent breeding-induced endometritis (PBIE) based on their ability to clear this inflammation/infection by 48 h post-breeding [3,4]. A normal phenomenon, post-breeding inflammation can be caused by infectious agents (i.e., bacteria and fungus) and or by non-infectious agents such as sperm [9] All mares display this transient uterine inflammatory response within 30 minutes following natural mating or artificial insemination [10,11,12]. This manuscript aims to revise the clinical, molecular, and microbiological aspects of the pathogenesis, diagnosis, and treatment of endometritis in mares
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