INFLAMMATION, INFECTION, OR BOTH? ROOT CAUSES OF ENDOMETRITIS


reach the oviduct after insemination, even in the pres- ence of pre-existing inflammation.8


5. Persistent Breeding-Induced Endometritis


A young, reproductively healthy mare will resolve the breeding-induced inflammation within 24 to 48hours.6 Since it is not practical tomonitor the elimi- nation of neutrophils or the change in the balance between anti- and proinflammatory cytokines, the


elimination of ultrasonographically visible uterine fluid and reduction in uterine edema are the most use- ful proxies for the successful completion of uterine clearance. In young, healthy mares, this usually takes up to 6hours after breeding with fresh semen but of- ten takes longer after frozen semen insemination (12hours).5 In mares “susceptible” to postbreeding en- dometritis, however, the normal uterine defense mechanisms are compromised such that the clearance of spermatozoa and inflammatory debris is not com- pleted within 48hours, and significant uterine fluid accumulation (> 2cm) will persist beyond the 6- to 12- hour time windows quoted above. As a result, it is ad- visable to check susceptible mares relatively soon af- ter artificial insemination, e.g., 4 to 6hours, to enable timely initiation of treatments to enhance uterine clearance and/ormodulate the inflammatory response. These additional treatments may be as simple as the use of ecbolics, such as oxytocin, to stimulate myome- trial contractions and enhance the expulsion of fluid or uterine lavage with sterile 0.9% saline or lactated Ringer’ssolution (LRS) to remove the fluid and any offending spermatozoa, bacteria, and inflammatory byproducts that it might contain.Early and aggressive management of PBIE very much improves the likeli- hood of rapid resolution and reduces the risk of sec- ondary infection. Therefore, in practice, it is important to identify mares likely to be susceptible to PBIE so that they can be monitored more intensively around the time of insemination, both to minimize the num- ber of inflammatory challenges (i.e., inseminations) and, following insemination, to ensure the rapid com- pletion of uterine clearance and dampening of the inflammatory cascade. While susceptibility to PBIE may only become evident following the first insemina- tion, the aged maiden mare is an obvious candidate for closer monitoring, and a thorough initial examina- tion may reveal predispositions to PBIE that need to be addressed.


6. Old Maiden Mare Issues


When presented with a teenagemaidenmare recently retired from competition, it is important to remember that she has no breeding history and, therefore, may have undiagnosed congenital anomalies or problems normally diagnosed in 3- to 4-year-olds. Recently retired sport horses may also be slow to start cycling at the start of the year because of low body-fat reserves or treatments received during their competi- tive career. The lack of body fat may also predispose


24 2022 / Vol. 68 / AAEP PROCEEDINGS


with cycle stage and follicle development).7 Since both fluidandexcessiveedema areindicators of inflamma- tion, if they are present, it is advisable to collect a uterine sample for cytological and microbiological investigation to rule out a pre-existing infection. Even if the fluid proves to be sterile and free of inflamma- tory cells, it can be advantageous to lavage themare’s uterus with LRS prior to insemination.9 In some cases, the fluid recovered may be very turbulent, sug- gesting excess mucus. A mucolytic agent, such as N- acetyl cysteine, can help to breakdown excess mucus by reducing disulphide bonds,6 thereby facilitating re- moval. In older maiden mares and older mares that have been used as embryo donors without ever giving birth, it is important to check cervical relaxation dur- ing estrus, preferably by digital examination. The cer- vix can be fibrotic, long, and tortuous. The fibrotic nature of the cervix becomes increasingly severe with an increasing number of years without foaling, and this change can significantly interfere with postbreed- ing uterine clearance. Cervical relaxation can be assisted by manual dilation at the time of insemina- tion and in combination with uterine lavage and/or ecbolic treatment at the first postbreeding examina- tion. In severe cases, topical application of prostaglan- din E products, e.g., 1mg of misoprostol (PGE1: Cytotec tablets dissolved in 0.9% saline or crushed and mixed with sterile gel) or 1mg of prostin E2 (PGE2; either in tablet or gel form), at around 4 to 6hours after inseminationmay further enhance cervi- cal relaxation and assist the evacuation of accumu- lated fluid. Probably the best long-term remedy for cervical fibrosis, however, is foaling since parturition involves a complete remodeling of cervical architec- ture at the level of the cells and extracellular matrix. The owners of a mare intended as an embryo donor may take some convincing that it is better to keep her in foal because establishing pregnancy in these mares may be a challenge.


to poor perineal conformation, adding an extra predis- position to pneumo- and urovagina and pre-existing infective endometritis. As a result, during the first ex- amination, more attention should be paid to carefully checking whether themare requires a Caslick’s proce- dure and for thepresenceof intrauterine fluid or inap- propriate edema (i.e., more edema than is consistent


7. Age-Related Degenerative Changes


even hasten fibrotic changes.10 Although the extent of fibrotic degeneration, and therefore the prognosis for carrying a foal to term, can be examined via an endo- metrial biopsy, there are no treatments proven to reverse the degenerative process. This means that a biopsy is most useful for highlighting the likely chal- lenge and/or helping to make the decision of whether to let the mare carry a pregnancy or to use her


Chronic endometrial degeneration is known to be more a factor of age than parity inmares. Therefore, a career as a sport horse is not protective against endo- metrial degeneration; in fact, years of barrennessmay


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