What's New in Equine Endometritis, Placentitis and Cloning

Issues in equine reproduction today may be as numerous as the potential advancements tomorrow.

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Originally published in the March 2015 issue of Veterinary Practice News.

The issues in equine reproduction today may be as numerous as the potential advancements in the field tomorrow. Endometritis and cloning have grabbed the attention of some experts, while others, such as Scott Bailey, DVM, Dipl. ACT, are focused on contraception and placentitis.

Dr. Bailey, an assistant professor of theriogenology at North Carolina State University’s College of Veterinary Medicine, said contraception isn’t discussed enough.  “A lot of performance mares really struggle with managing behavior in the face of a competition schedule,” Bailey said.

Owners he’s spoken with feel strongly that mares don’t do as well as geldings.

“There are statistics that show that when they are in heat and in competition they are less likely to jump their best or race their best or win first place,” he said.

Contraception is an issue for owners who want their horses to do as well, and it’s important from the standpoint of population control, Bailey said.

“We still are faced with an overpopulation of horses in the U.S.,” he said, adding that when he applies for research grants related to equine reproduction, “We very often get the question back, ‘Why should we breed? There are too many horses.’

“That’s one thing as equine veterinarians we all need to address,” he added.

The other topic on Bailey’s mind is the most common cause of pregnancy loss: placentitis, or inflammation of the placenta because of bacteria ascending to the cervix. The condition affects about 5 percent of pregnancies, he said.

That is Bailey’s research focus, and he is looking at which treatments are effective.

“In clinical trials we’ve identified a number of things that maybe can and don’t work,” Bailey said.

A first step with placentitis is for veterinarians to diagnose it early, using ultrasound and knowing the clinical signs and the horse’s history of aborting a pregnancy, he said.

“The most common clinical sign is early mammary development, more than three weeks before she’s due,” Bailey said.

To diagnose the problem, measure the combined thickness of the uterus and placenta.

“It’s something that most veterinarians can do but it takes some practice,” Bailey said.

Treatment  involves long-term antibiotic and anti-inflammatory therapy combined with a synthetic progesterone, altrenogest. Bailey’s laboratory research has found that pentoxyfilen isn’t an effective anti-inflammatory and that trimethoprim/sulfamethoxazole doesn’t perform well as an antibiotic. Bailey plans to publish his research this year. After that, Bailey and his team will look for another drug. Penicillin is off the list because it treats only a subset of bacteria—it goes after Gram-positive bacteria, but the disease can be either Gram-positive or Gram-negative.

Also not on the list are drugs that require injections. Treating mares with daily injections during pregnancy is problematic. Oral drugs are cheaper and don’t require a veterinarian on the farm every day to give an injection, Bailey noted.

“We would like something else that is oral that works, and so far we haven’t found oral that works,” he said.

A CSU equine veterinarian conducts an ultrasound at the university’s well-regarded Equine Reproduction Laboratory.

Colorado State University

A CSU equine veterinarian conducts an ultrasound at the university’s well-regarded Equine Reproduction Laboratory.


Endometritis is a top problem that gets the attention of Pat McCue, DVM, Ph.D., Dipl. ACT.

“One of the most common issues in broodmare practice is endometritis, or inflammation of the uterus,” said Dr. McCue, the Iron Rose Ranch Professor of Equine Theriogenology and a faculty member at Colorado State University.

The causes of endometritis may be subdivided into infectious and noninfectious causes, he noted.

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“The most common noninfectious cause is mating-induced endometritis, in which spermatozoa from the stallion elicit an inflammatory response,” McCue said. “A transient inflammatory response in the endometrium is an inevitable consequence of mating by either natural service or by artificial insemination in all mares.”

The normal inflammatory response begins within a half hour after insemination, reaches a peak by eight to 12 hours and is usually resolved by 24 to 48 hours, McCue said.

“A persistent post-mating inflammatory response may develop in older susceptible mares that cannot physically clear fluid and inflammatory products from their uterus,” he said. “Inadequate or insufficient muscular contractions of the uterus is the most common cause for the retained fluid and persistent inflammation.”

If the inflammation persists, the embryo will not survive when it enters the uterus five to six days after ovulation, McCue said, adding that “persistent uterine inflammation may result in premature destruction of the corpus luteum and result in lower progesterone levels or short cycling.”

The aim of managing mating-induced endometritis, McCue said, is to limit the severity and duration of the inflammatory response and to clear the uterus of fluid, sperm, inflammatory byproducts and bacteria.

“Ideally, a mare susceptible to persistent mating-induced endometritis should be bred or inseminated only once during an estrous cycle, and the breeding should be timed to occur immediately prior to ovulation,” he said. “The uterus may be lavaged with sterile saline or sterile lactated Ringer’s solution four to six hours after mating.”

To perform the lavage procedure, McCue advises infusing 1 liter of fluid into the uterus at a time and repeating the process until the recovered fluid is clear.

Oxytocin may be administered beginning four to six hours after mating to stimulate uterine contractions and assist with the physical clearance of fluid and inflammatory byproducts, he added.

McCue said infectious endometritis, on the other hand, is most commonly caused by bacteria and is a significant cause of decreased reproductive performance in mares due to the failure of conception or early embryonic loss.

“A majority of young mares rapidly eliminate bacterial contamination of the uterus following mating, parturition intrauterine manipulations or other events, and are considered to be resistant to infection,” he said.

Some older mares that are multiparous, may not be able to spontaneously eliminate pathogenic organisms from their uterus, making them more susceptible to infection, he added.

Factors that predispose mares to uterine infections may include contamination at breeding, pooling of urine in the anterior vagina and uterus, trauma from parturition or breeding, and failure of natural uterine defense mechanisms, he said.

“Poor perineal conformation, decreased muscular tone of the vulva and cranial displacement of the anal sphincter may lead to aspiration of air and fecal material into the reproductive tract,” he added.

To detect a mare that is susceptible to chronic uterine infections, one examines the breeding history and a reproductive evaluation, McCue said. Affected mares may have a history of short cycling, repeated uterine infections or failure to conceive after having been bred to a fertile stallion, he added.

“Examination of the uterus by transrectal ultrasonography to detect the presence of intrauterine fluid is a practical method for identifying mares with a delay in physical clearance and possible susceptibility to infection,” he said.

Cytologic examination of an endometrial swab may reveal white blood cells. A culture may detect a specific organism, and an endometrial biopsy may be useful in predicting susceptibility, because mares with poor biopsy scores are more likely to be susceptible to infection than mares with Grade I biopsy scores, McCue said.

The center’s focus is producing healthy foals – future talent for working and performance.

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Colorado State University

The Colorado State University’s Equine Reproduction Center's focus is producing healthy foals – future talent for working and performance.

Endometritis Treatments

Numerous protocols exist for the treatment of endometritis. McCue said the most common bacterial organisms cultured from mares with chronic endometritis are Streptococcus zooepidemicus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae.

“The general principles of a treatment regimen are to remove the source of infection, aid in physical clearance of the uterus, eliminate pathogenic organisms by local infusion with antimicrobial agents and reduce future contamination by enhanced reproductive management,” McCue said.

Treatment often includes uterine lavage to remove fluid, inflammatory byproducts and bacteria, followed by infusion of antibiotics into the uterus. If the perineal conformation is poor or the muscular tone of the vulva is inadequate, a Caslick procedure may be warranted to prevent recontamination, said McCue, who recommends a followup examination and culture to confirm the infection has been eliminated.

For Jos Mottershead, president of Equine-Reproduction.com in Wynnewood, Okla., one of the top issues in equine production is the correct diagnosis of uterine conditions in mares.

For many years the standard evaluation has been a swab culture  to determine uterine pathogenic status, Mottershead said.

“Unfortunately, it has been clearly demonstrated that a uterine swab culture alone is inadequate at correctly demonstrating the pathogenic status of the uterus,” he said.

The practice has the potential to be both inadequate and inaccurate, and a cytology brush yields a better sample than a culture swab, Mottershead said.

“The use of a uterine swab culture coupled with a microscopic cytological smear evaluation—the latter being rapidly, cheaply and effectively performed in-house—offers a combination of good diagnostic ability coupled with cost-effectiveness for the client,” he said.

In stallions, the issues are correct semen collection and preparation, Mottershead said.

“First, there is no one-size-fits-all semen extender,” Mottershead said. “Stallions are all individuals, and so is their semen.”

Once the correct extender has been dealt with, safe and effective semen collection techniques should be implemented, followed by proper semen evaluation and packaging for shipment.

“We receive a high percentage of poor quality shipments each year, and in many cases those shipments could have been improved if quality of preparation had also improved,” Mottershead said.

General Practitioners

North Carolina State’s Bailey foresees more equine practitioners having a hand in treating reproduction issues.

Many veterinarians are capable of performing artificial insemination and freezing semen, but Bailey said the key for veterinarians is to understand what’s valuable to their practices and clients. These include embryo transfer and techniques for ovum pickup—an individual egg or a group of eggs may be processed by intracytoplasmic sperm injection.

“It has its complications and it can be very successful,” Bailey said.

If, for example, a prized mare dies from a sudden injury, the entire ovary may be harvested and sent for processing and for the intracytoplasmic sperm injection procedure, or eggs may be taken and sent out. If a stallion dies, semen may be collected.

“That’s something that any veterinarian that has access to FedEx can do if they are faced with a valuable mare that either has an acute injury or an acute illness that results in their death,” Bailey said. “I think many veterinarians don’t realize it, but in that emergency situation they can offer that to the owner. I think that goes a long way to make them feel better about the death of their horse.”

 Dr. Pat McCue, CSU professor of equine theriogenology, analyzes sperm health at the university’s Equine Reproduction Laboratory.

Colorado State University

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Dr. Pat McCue, CSU professor of equine theriogenology, analyzes sperm health at the university’s Equine Reproduction Laboratory.


Cloning is another way of perpetuating a treasured horse, Bailey noted. The procedure may be more successful and easier than intracytoplasmic sperm injection, he added.

“Cloning is being performed on probably over 200 horses and is a fairly successful means of preserving genetic material,” Bailey said.

There is no guarantee of duplicating a horse’s performance, Bailey said, but the idea would be to breed the cloned horse and have the offspring eventually perform.

Why not have the cloned equine race or jump?

The problem, Bailey said, is that if the horse doesn’t perform as well as its progenitor, its breeding potential could be diminished or eliminated.

“The value of a clone really is to take a Secretariat, or an Olympic gold medal exceptional horse that can’t produce offspring of its own, and produce offspring in the future,” Bailey said.

Mottershead also sees cloning as the next big step in equine reproduction.

“What many are unaware of is that there is the potential to modify certain gene markers during the cloning process,” he said, “and that could lead to the cloning of a horse that carries some negative genetic trait, but removing the trait during the cloning process,” Mottershead said.

For example, he said, one could theoretically clone the American quarter horse sire Impressive but remove the hyperkalemic periodic paralysis gene—HYPP is an inherited muscle disease—or take a hereditary equine regional dermal asthenia (HERDA) carrier and produce a horse capable of reproducing naturally without replicating a negative genetic problem.

“Then of course we have to wonder with the mapping of the horse genome about the possibilities of not only turning markers off but also tuning them on,” Mottershead said.


One of the major advancements McCue has seen is in the detection of infectious endometritis with the incorporation of molecular diagnostic techniques.

“Polymerase chain reaction can be used to detect minute quantities of the nucleotide sequence of DNA of bacterial or fungal organisms,” McCue said. “The most practical use of PCR technology in equine reproduction is the detection and identification of bacterial or fungal DNA in the uterus of problem or infertile mares in which traditional culture fails to detect an organism and there is a high index of suspicion of an infection based on reproductive history or other diagnostic tests.”

PCR technology should become available in equine veterinary practices in the next two to three years, he said.

The advantages of PCR examinations include rapid analysis of a sample, extreme sensitivity and the potential to detect microbial DNA in cases of infectious endometritis where a traditional culture was unsuccessful, McCue said.

Additionally, early detection of an infection enables practitioners to make informed clinical decisions regarding antimicrobial therapy days before traditional culture results would be available, he said. 

Aspects that Mottershead sees pushing equine reproduction forward into the 21st century include improved techniques for semen freezing embryo transfers.

These practices, which 20 years ago were considered leading edge, are now commonplace but improving further, he said.

“DNA testing has resolved many of the fears about mistakes or fraudulent usage of the techniques, and now we have the opportunity to advance breeding programs by producing foals from 2-year-olds—or even yearlings, in some cases—by the use of embryo transfer,” Mottershead said.

“At the other end of the extreme, we have the ability to maintain a stallion's genetics well beyond his death with the use of frozen semen.”

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