INFLAMMATION, INFECTION, OR BOTH? ROOT CAUSES OF ENDOMETRITIS
primarily as an embryo or oocyte donor. Symptomatic treatment for endometrial degeneration can include more frequent use of ecbolics postinsemination, since endometrial degeneration has been associated with reduced myometrial contractility as a result of an accumulation of nitric oxide,5 and hysteroscopic re- moval of large endometrial cysts using electrocautery or an Nd:YAG laser. Oldermares are also more likely to be affected by oviductal blockage, and repeated fail- ure to establish pregnancy or recover an embryo with- out any obvious underlying cause are reasons to consider oviductal therapies. Laparoscopic11 or intrau- terine application of PGE2 or hysteroscopic hydrotu- bation12 are all therapies known to restore oviductal patency. PPID is another condition of the older horse that can predispose mares to PBIE by compromising the normal immune response. Proper diagnosis of PPID and management using pergolide can help nor- malize both the postbreeding inflammatory reaction and possible abnormalities of cyclicity.13
8. Breeding Management of the Teenage Mare
addition, flushing the uterus with LRS to remove fluid 0 to 2hours prior to insemination can help pro- vide a “clean” starting point, and timing the insemi- nation further in advance of ovulation than normal (e.g., 18–24hours instead of 6–12hours) will allow extra time to resolve any issues with persistent uter- ine inflammation. Following insemination, early (4– 6hours postinsemination) identification and removal of fluid using a combination of large-volume uterine lavage, uterotonic agents such as oxytocin or a PGF2a analog, and cervical dilation is also essential to limiting the duration of the uterine inflammatory response.6With respect to the uterotonic drugs, some studies suggest that lower doses of oxytocin (5–10IU) may be more effective in promoting uterine clearance than higher doses (> 20IU) because the latter cause a nonproductive uterine “spasm” rather than waves of contraction.14 And while PGF2a analogs, such as clo- prostenol, are useful alternatives to oxytocin because of their longer duration of action (4–5hours compared to < 45minutes), their use postovulation is not recom- mended because it will compromise subsequent cor- pus luteum function.15 In some susceptible mares, conventional treatments appear to be inadequate to resolve the postbreeding inflammatory reaction in a timely fashion, and it may be worth considering the use of systemic corticosteroids tomodulate the inflam- matory reaction. Both a single large dose of dexamtho- sone16 and daily administration of prednisolone17 have been reported to improve the likelihood of
Since it is safest to assume that a teenage maiden mare is at increased risk of susceptibility to PBIE, efforts should be made to ensure a minimal number of inseminations per cycle. This will include frequent (at least daily) monitoring of follicle development, combined with the use of an ovulation-inducing agent (i.e., human chorionic gonadotropin [hCG] or a gonadotropin-releasing hormone [GnRH] analog); in
pregnancy or embryo recovery in susceptible mares. Corticosteroids also appear to limit postinsemination edema and fluid accumulation and correct deviations in the balance between pro- and anti-inflammatory cytokines reported during PBIE.
9. Conclusions
Sport horse mares submitted for breeding often fall into two distinct populations. Young mares prior to a competitive career are typically resistant to PBIE and require little specific postbreeding management; moreover, having a foal at a young agemay help delay the subsequent development of cervical fibrosis. Mares retired to breeding after a successful competi- tive career present a different challenge and are com- monly affected by fibrotic degeneration of both the cervix, which interferes with the ability to relax and allow the elimination of fluid, and the endometrium, which may compromise both myometrial contractility and the ability to provide an environment conducive to embryo development and placentation. One of the most important aspects of managing the retired sport horsemare is therefore early postbreedingmonitoring for fluid and simple but aggressive therapies to enhance uterine clearance and limit the duration of inflammation.
Acknowledgments
Declaration of Ethics The Author has adhered to the Principles of Veteri- naryMedical Ethics of theAVMA.
Conflict of Interest The Author has no conflicts of interest.
References
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AllenWR.Reproductive efficiency of intensively managed Thoroughbred mares in Newmarket. Equine Vet J 2002;34:51–60.
2. Cuervo-Arango J, Claes AN, Stout TA. A retrospective com- parison of the efficiency of different assisted reproductive techniques in the horse, emphasizing the impact of mater- nal age. Theriogenology 2019;132:36–44.
3. Mortensen CJ, Choi YH, Hinrichs K, et al. Embryo recovery from exercised mares. Anim Reprod Sci 2009;110:237–244.
4. Stout TA. Clinical application of in vitro embryo production in the horse. J Equine Vet Sci 2020;89:103011.
5. Troedsson MH. Breeding-induced endometritis in mares. Vet Clin North Am Equine Pract 2006;22:705–712.
6. Morris LHA, McCue PM, Aurich C. Equine endometritis: A review of challenges and new approaches. Reproduction 2020;160:R95–R110.
7. LeBlanc MM. Advances in the diagnosis and treatment of chronic infectious and post-mating-induced endometritis in the mare. Reprod Dom Anim 2010;45:21–27.
8. Troedsson MHT, Esteller-Vico A, Scoggin KE, et al. Equine seminal plasma derived lactoferrin regulates binding of polymorphonuclear neutrophils to spermatozoa. J Equine Vet Sci 2014;34:49.
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