Elsevier

Theriogenology

Volume 64, Issue 3, August 2005, Pages 580-588
Theriogenology

Post-breeding inflammation and endometrial cytology in mares

https://doi.org/10.1016/j.theriogenology.2005.05.041Get rights and content

Abstract

Endometritis has been reported to be the third most common medical condition of horses. Timely diagnosis and treatment of endometritis in mares increases the chance of pregnancy. Exfoliative endometrial cytology is often used as a clinical tool to evaluate endometrial inflammation through detection of neutrophils. There is a lack of information on the time frame for changes in endometrial cytologic parameters following breeding. The main objectives of this article are to use current information to describe systematic analysis of endometrial cytology using standardized methods for sample collection and interpretation, and discuss how these parameters change in relationship to post-breeding interval and mare susceptibility.

Introduction

The acute endometrial inflammatory response after breeding is a predictable, physiologic event following the introduction of spermatozoa, bacteria, and contaminants [1]. Seminal plasma depresses the endometrial inflammatory response to spermatozoa, and is present in mares bred by live cover, or artificial insemination with fresh or cooled-transported semen [2].

During the process of cryopreservation, seminal plasma is removed to concentrate the spermatozoa. A proportion of all mares bred develop persistent endometrial inflammation. Kotilainen et al. [3] collected intrauterine fluid 6 h post-breeding with frozen semen or extender and reported higher numbers of neutrophils in mares bred with frozen semen. Other factors that contribute to the marked persistent inflammation in mares bred with frozen semen include: removal of seminal plasma during the process of cryopreservation; allergic-type hypersensitivity reactions to components of the freezing extenders (e.g. glycerol and egg yolk); or delayed uterine clearance, as reported in mares susceptible to endometritis [4], [5]. However, the marked endometrial inflammation following breeding with frozen semen is not commonly observed in young virgin mares [6].

Sperm-induced persistent endometrial inflammation has been suggested to contribute to lower fertility in mares by altering the uterine microenvironment and hindering embryonic survival. Mares with persistent inflammation typically have a number of predisposing factors, such as poor perineal conformation, a dependent uterine location, and delayed uterine clearance due to suboptimal myometrial contractility. They are termed “susceptible” to endometritis and experimentally are unable to clear (within 96 h) an intrauterine bacterial challenge with Streptococcus equi zooepidemicus. Mares that are able to clear the bacteria are termed “resistant” to endometritis. The susceptible mare, frequently due to poor perineal conformation, has more bacterial contamination of her reproductive tract than a resistant mare. It follows that more bacteria are available to be introduced at breeding, or are already present in the uterus at the time of insemination in a susceptible mare rather than a resistant mare. Other physical factors such as a dependent uterine location further disadvantage a susceptible mare; the myometrium contracts against gravity to remove the residual sperm and debris [7].

Peak endometrial inflammation is reached 12–24 h after breeding [3], [8]. The embryo leaves its tubal phase on about day 5 post-ovulation, therefore uterine inflammation must be controlled by 96 h post-ovulation to maximize survival of the embryo. There is a lack of information regarding: changes in endometrial cytology following breeding, the decrease in inflammation following the peak, the inflammatory response in mares that are susceptible versus resistant to endometritis, and whether the lack of seminal plasma influences the inflammatory response in mares bred with frozen-thawed semen.

Early detection of non-physiologic endometrial inflammation through techniques such as transrectal palpation/ultrasound and endometrial cytology, coupled with timely intervention to manage persistent endometrial inflammation, are required to increase pregnancy rates.

Section snippets

Detection of endometrial inflammation

The detection of persistent post-mating inflammation in mares is a clinical challenge. It is usually performed by serial daily transrectal palpations and ultrasound examinations of the reproductive tract. Poor uterine tone and the presence of free intrauterine fluid are associated with delayed uterine clearance and persistent inflammation [7], [9]. Highly fertile mares seldom have free intrauterine fluid following breeding [6]. The relevance of the uterine fluid accumulation is evaluated by

Non-bred mares

Endometrial cytologic parameters (neutrophil percent, bacterial score, or debris) are similar from 24 to 96 h after ovulation in non-bred mares [16]. There is a constant resident population of neutrophils (<5%) present in an exfoliative cytology [3], [16] 24–96 h after ovulation. Bacterial scores are 1 bacterium per 30 fields, and <25% debris per high-power field using the cytocentrifuge technique 24–96 h post-ovulation [24].

Bred mares

Peak inflammation post-breeding is reached before 24 h. Mild inflammation,

Discussion

Persistent post-breeding endometritis is of concern to practitioners and breeders, due to its association with lower fertility. At the present time practitioners, do not have a normal range of endometrial cytologic parameters that allow them to evaluate mares post ovulation or post-breeding to determine if intervention is necessary. The presence of >5% neutrophils indicates that endometrial inflammation is present and may require further intervention. The decision to treat a mare for persistent

Acknowledgements

Thanks to the Alberta Agriculture Research Institute and the Equine Health Research Fund of the Western College of Veterinary Medicine for financial support.

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    A practical method for recognizing mares susceptible to post-breeding endometritis

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    Mares susceptible or resistant to endometritis have similar endometrial echographic and inflammatory cell reactions at 96 hours after infusion with frozen semen and extender

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