EVJ Calls for More Broodmare Reproduction Research

While there have been significant advances in equine reproduction techniques in recent years there has been a shortage of research on reproductive problems in broodmares, according to the Equine Veterinary Journal (EVJ).

The EVJ’s new online reproduction research collection, with an introduction from equine reproduction expert Jon Pycock, BVetMed, PhD, DESM, MRCVS, new president of the British Equine Veterinary Association, aims at engaging interest to potentially address this shortfall.

Equine reproduction is of pivotal importance in equine veterinary medicine both in practical and commercial capacities. There have been significant advances in both natural breeding and artificial breeding techniques. Artificial insemination success rates have improved; embryo transfer has become a common procedure and advanced techniques, such as intracytoplasmic sperm injection, are now being used with success. Equine stud medicine currently accounts for a significant proportion of veterinary business.

Although there is a dearth of research on reproduction and the broodmare the quality and innovative nature of the papers that have been published over the past four years present a valuable source of information for the equine practitioner. The new online collection comprises ten papers chosen by Pycock.

Transient post-breeding endometritis in susceptible mares can adversely affect pregnancy rate. One of the articles in the collection reviews the current research on inflammatory mechanisms of endometritis, focusing on endometrial gene expression. Another paper evaluates the roles of corticosteroids and immunomodulators in controlling inflammatory responses to prevent post-breeding endometritis. A further study looks at the systemic treatment of infectious endometritis using the respiratory treatment cephalosporin.

Despite a lack of scientific evidence many vets regularly use exogenous progestins in the belief that it reduces the incidence of early pregnancy failure. A speculative report in the collection describes a pregnancy that was successfully rescued possibly because of the administration of oral altrenogest, which could represent a documented case of luteal insufficiency.

Fertility in mares declines with age but the various reasons for this are poorly understood. One of the studies has found a positive correlation between anti-Mullerian hormone (AMH) concentration and antral follicle count (AFC) concentration in older mares and concludes that AMH concentration could be a better reflection of reproductive age than calendar age.

Horses are known to be “long-day breeders,” but artificial light in stables or barns is commonly used to further advance the Thoroughbred breeding season. One of the papers describes the use of individual light masks, similar in design to racing blinkers, which enable the mares to remain outside. This has cost, management, and welfare advantages.

Relatively little is known about the equine oviduct, despite it playing a fundamental part in the fertilization process. One of the papers in the collection explains the novel technique of hysteroscopic hydrotubation of the oviduct via the uterotubal junction, which could present an easier way to investigate oviduct function and any abnormalities.

Twin pregnancies are common in clinical practice and one conceptus is usually reduced manually. However, little is known about the effects of the crushing procedure on the live foal. Another study identified that in mares more than nine years of age that had undergone a manual twin elimination the live foal rate was less than in similarly aged mares with a single conceptus.

While anovulatory hemorrhagic follicles are the most common ovarian abnormality in the mare the causes are, as yet, unknown and treatment is limited. One of the studies demonstrates the ability of prostaglandins to eliminate the stimulated induction of anovulatory follicles.

Various therapeutic options have been explored to repress estrus-associated behavior in mares, including a gonadotropic-releasing hormone (typically referred to as GnRH) vaccine. However, irreversible suppression of reproductive function is not usually desirable. One of the studies found that the vaccine is reversible although it took longer in younger mares and, in some cases, could take as long as 720 days.

“Together, the papers in this online collection provide insight on a number of the clinical challenges currently facing veterinarians involved in broodmare practice,” said Celia Marr, BVMS, MVM, PhD, Dipl. EIM, ECEIM, MRCVS, EVJ editor. “Numerous gaps in knowledge remain, and to counter this the EVJ intends to continue to publish important and relevant studies in this field. In future years we hope to see an increase in quantity of pertinent studies to match the undoubted quality of the reproductive research in this collection.”

Pycock added, “We very much hope that this collection will not only help to inform and educate but also inspire interested parties to conduct further studies to build our knowledge and expertise in this important area.”

The collection is available free online at onlinelibrary.wiley.com/journal/10.1001/(ISSN)2042-3306/homepage/progress_in_broodmare_practice.htm.

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