IN-DEPTH: REPRODUCTIVE ENDOCRINOLOGY


whereas cloprostenol induced low-amplitude myo- metrial contractions that lasted 4 to 5 hours. This sustained effect is particularly desirable to enhance lymph flow and consistent intraluminal evacuation of accumulated fluid (inflammatory transudate). Despite its indisputable efficacy as an ecbolic hor- mone, the use of PGF during estrus, especially in the early post-ovulatory period, was found to tran- siently affect luteal function. Some studies con- firmed this effect on luteal function that was followed by a resurgence in CL function.17,18 It is unknown whether this early effect in suppressing luteal function would affect the fertility of treated mares. For this reason, if PGF is to be used as an ecbolic to treat delayed clearance during estrus and early postovulatory period, it is important that equine practitioners remain cognizant of its effects on luteal function. Most mares so treated should have resurgence in luteal function and not have deleterious effects on their luteal function and sub- sequent fertilities.19 Moreover, our laboratory has recently reported that the effect of PGF administra- tion on early luteal function can induce luteolysis or antiluteogenesis, depending on the duration of treatment after ovulation and on dosage used.3 For these reasons, treatments with PGF during es- trus should not continue beyond 24 hours after ovu- lation. Whenever indicated, low doses of PGF (eg, 62.5–125 g cloprostenol or 1.25 mg dinoprost), which are capable of inducing uterine contractions, are recommended for treating mares with delayed uterine clearance.


7. Modulation of Mating-Induced Endometritis With Steroids


Endometritis after artificial insemination or mating is one important cause of infertility especially in mares susceptible to persistent mating-induced endometritis. In addition to therapies aimed at combating endometritis by use of intrauterine or systemic antibiotic treatment and stimulation of myometrial function through administration of ec- bolic hormones (mainly oxytocin and PGF), another strategy is to control or modulate the exacerbated inflammation response seen in these mares. Dell’Aqua et al20 first reported on the efficacy of prednisolone treatment of mares during estrus that benefited from the glucocorticoid modulatory effects on barren mares afflicted with endometritis. A significantly higher pregnancy rate was seen in bar- ren mares treated 5 times with 0.1 mg/kg of pred- nisolone acetate (50 mg per mare) administered every 12 hours with four treatments occurring be- fore artificial insemination (AI) and one at AI. In 2008, Morris reported promising results used the same protocol described by the Dell’Aqua, except she used a dose of 200 mg of oral prednisolone per mare. More recently, Bucca et al,21 reported on the use dexamethasone given as a single bolus admin- istration of 50 mg per mare at time of breeding. In that study, the authors concluded that dexameth-


asone administered at the time of artificial insemi- nation was safe and effective for modulating persistent mating-induced endometritis in suscepti- ble mares; the glucocorticoid treatment decreased endometrial edema, accumulation of intraluminal uterine fluid and its turbidity, without altering the amount of polymorphonuclear cells seen in prepara- tions obtained from endometrial cytology. Ferris and McCue22 studied the effects of multiple (twice daily for 5 days) glucocorticoid treatments (pred- nisolone or dexamethasone in mares during early estrus. They reported that mares treated with dexamethasone showed reduced uterine edema and ovulation rate (40% versus 83%, respectively) than mares treated with prednisolone. In addition, only two of five dexamethasone-treated mares had unal- tered LH hormonal profiles, whereas five of six mares treated with prednisolone had LH surges within normal limits. The differences noted be- tween dexamethasone and prednisolone may derive from their differences in relative potencies in rela- tion to cortisol (dexamethasone  30; pred- nisolone  4). Nevertheless, it is unlikely that a single treatment with dexamethasone as prescribed by Bucca and Carli21 would result in ovulation fail- ure as only mares with multiple, daily treatments with dexamethasone have been shown to have al- tered endogenous LH release that resulted in signif- icant ovulation failures. It is important, however, to ensure that mares being treated with glucocorti- coids during estrus are also treated with ovulation- inducing agents to prevent any potential negative effects of glucorticoid agents in the hypothalamic- hypophyseal axis that may result in anovulation. Bucca et al23 provided supporting evidence to the efficacy of associating induction of ovulation with glucocorticoid treatment in mares susceptible to per- sistent post-mating endometritis. Mares treated with a single bolus intravenous injection of 50 mg of dexamethasone within 1 hour of breeding and con- current induction of ovulation with 1500 IU of hCG exhibited normal ovulation rates (97% of mares ovulated within 48 hours). The minimal dose of prednisolone and dexamethasone to combat inflam- mation in mares during estrus has yet to be determined.


8. Conclusions


Several pharmacologic agents are now available for use in the breeding management of broodmares. Strategic utilization of hormones to induce estrus and ovulation and to modulate/prevent inflam- matory processes in mares susceptible to mating- induced endometritis and delayed uterine clearance can significantly affect the outcome of breeding by increasing the odds of timed ovulation and pregnancy.


References and Footnotes


1. Oxender WD, Noden PA, Louis TM, et al. A review of pros- taglandin F2alpha for ovulation control in cows and mares. Am J Vet Res 1974;35:997–1001.


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