Problem Mares: Understanding Fertility Challenges and the Options Available
- June 25, 2026
At Twemlows, we regularly work with mares that have experienced difficulties becoming pregnant, maintaining a pregnancy, or producing a foal. These mares are often referred to as “problem mares” in the breeding industry, but the term encompasses a wide range of reproductive challenges.
To learn more about how these cases are approached, we spoke with our veterinarian, Rebecca Keating, DrMed Vet MRCVS, about the most common causes of subfertility, the available investigations, and the options available to owners.
What is a "problem mare"?
A “problem mare” is a mare that has difficulty conceiving, maintaining a pregnancy, or producing a foal despite being bred over three cycles to a stallion of proven fertility: in other words, a stallion that already has foals on the ground.
It is important to stress that this label does not mean the mare is infertile. In many cases, mares go on to produce healthy foals once the underlying cause has been identified and appropriately managed.
What happens when a mare is referred to Twemlows for fertility investigation?
We begin by reviewing the mare’s reproductive history, including previous pregnancies, breeding records, age, foaling history, treatments and any known issues.
A reproductive and speculum examination is then carried out, typically including ultrasound assessment and evaluation of the mare’s perineal conformation.
Investigations are approached systematically, starting with the most likely causes and ruling out problems step by step to reach an accurate diagnosis.
We also discuss the owner’s goals, budget, and timescale so that the plan is practical and realistic.
Further tests may include:
- Uterine bacterial culture and cytology
- Hysteroscopy to view the inside of the uterus
- Endometrial biopsy for specialist laboratory assessment
Each investigation is tailored to the mare and owner, to identify likely causes and create a realistic plan to improve reproductive success.
Are there particular conditions that you see frequently?
In sport horse breeding, stallion-related factors are a common challenge. Many stallions are competing, in high demand, or only available in very small semen doses.
Small doses can work well, but some mares need consistently high semen quality. Changing stallions is not always simple, particularly where owners are tied to a contract or committed to a specific mating.
IVF/ICSI can help in these cases, as only a small amount of semen is needed, and a single sperm is injected directly into the egg. This can be useful with some sub-fertile stallions, especially those with a proven ICSI record.
Another common issue is endometritis, or inflammation of the uterus, which may be caused by infection or an exaggerated response after breeding. Other conditions we investigate include:
- Age-related changes to the uterus
- Poor vulval conformation
- Urine pooling
- Oviductal blockage/abnormalities
- Early embryonic loss
- Lesions to the cervix
Fertility problems are often multifactorial, so a thorough, structured investigation is essential.
Wider health issues can also affect fertility. Dental disease, chronic pain, lameness and other concerns should therefore be considered as part of the overall assessment.
Once a diagnosis has been reached, a treatment and management plan is tailored to the individual mare.
This may include medical treatment for uterine inflammation or infection, changes to breeding management, or surgical procedures where appropriate. The goal is always to address the underlying cause and maximise the mare’s chances of producing a successful pregnancy.
Twemlows offers advanced reproductive techniques such as Embryo Transfer and OPU/ICSI. Are these always necessary?
No. Although advanced reproductive technologies can be extremely valuable, they are not always the first or only option. Many mares with fertility challenges can achieve successful pregnancies once an accurate diagnosis has been made and the underlying issue is treated appropriately.
For some mares, however, assisted reproductive techniques may offer the best and most cost-effective route. This may include mares with significant uterine disease, mares that are unable to carry a pregnancy, mares with limited breeding opportunities, or cases where semen availability or stallion fertility is a major factor.
In these situations, options such as Embryo Transfer, OPU and ICSI can provide alternative ways to produce a foal. The key is to choose the right technique for the right mare, at the right time.
What makes Twemlows well placed to manage these cases?
· Specialist reproductive expertise
One of Twemlows’ greatest strengths is the depth of reproductive expertise available on site. The reproductive service has been overseen by Monica Morganti for 14 years. After graduating, Monica completed two years of advanced training at UC Davis before passing both her European and American board examinations to become a Diplomate in Animal Reproduction.
This level of specialist qualification is relatively uncommon within equine practice and allows complex fertility cases to benefit from a high level of reproductive knowledge and experience.
· A dedicated stud medicine team
I have worked alongside Monica for seven breeding seasons and am currently completing my own specialist training in reproduction. Together with our junior assistants, we work exclusively in stud medicine on a full-time basis, allowing us to focus entirely on reproductive management and assisted breeding techniques.
· Experience across a wide range of mares and stallions
Over the years, we have managed thousands of mares and worked with semen from a wide range of stallions. That experience is invaluable when dealing with fertility cases, as recurring patterns can help guide investigations and treatment plans.
· Facilities designed around breeding mares
Twemlows has specialist facilities designed specifically for breeding mares. Unlike many general veterinary practices, the daily routine is centred around optimising each mare’s reproductive cycle.
Every mare is managed as an individual. Some may only require one scan each day, while others may need multiple examinations to accurately monitor ovulation, breeding timing or response to treatment.
· A full range of reproductive options
In addition to fertility investigations and treatment, we offer a complete range of assisted reproductive technologies, including Embryo Transfer, OPU and ICSI, supported by an extensive recipient mare programme. This allows mares to move seamlessly from diagnosis through to treatment and advanced reproductive procedures when required.
· A tailored approach for every mares
Ultimately, our approach is centred on finding the most appropriate solution for each mare. Whether that involves straightforward fertility management or advanced procedures such as Embryo Transfer or OPU/ICSI, the aim is always to maximise reproductive success while tailoring the plan to the individual mare and her owner’s goals
