Older mares in breeding: managing with care
Using older Thoroughbred mares in breeding programs is common, but age brings a few curveballs. Fertility dips and health risks rise, but with the right care and attention, these mares can absolutely continue producing strong, healthy foals.
Let’s break down the science, challenges, and solutions.
What challenges do older mares face?
Declining fertility:
Mares over 15 often show reduced fertility, driven by factors like uterine degeneration, hormonal imbalances, and lower ovarian activity. (Ball et al., 2008)
Uterine health issues:
Endometritis, an inflammation of the uterine lining, is more frequent in older mares due to reduced uterine clearance. Chronic inflammation can affect both conception and pregnancy maintenance. (LeBlanc, 2010)
Foaling complications:
Older mares are at higher risk of dystocia (difficult foaling), retained placentas, and other postpartum issues. These can threaten both mare and foal.
General health concerns:
Conditions like arthritis, Cushing’s Disease (PPID), and metabolic disorders become more common with age, and they can impact a mare’s ability to safely carry and deliver a foal.
How breeders manage these risks
Pre-breeding evaluations:
Reproductive exams, often using transrectal ultrasound and uterine biopsy, help breeders assess the health of the uterus, ovarian activity, and readiness for pregnancy. Hormonal assays can also identify imbalances like low progesterone, which may require treatment. (Ricketts & Alonso, 1991)
Optimising nutrition:
Older mares need tailored diets to maintain an ideal body condition score (BCS) of 5–6 out of 9.
This typically includes:
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High-quality forage and grain
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Joint supplements (like glucosamine) and metabolic support
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Vitamins and minerals, especially vitamin E and selenium for immune function
Reproductive technologies:
Advanced tools improve success rates. One common example is oxytocin therapy, used to help clear fluid from the uterus in mares prone to retention. (LeBlanc, 2010)
Monitoring pregnancy closely:
Older mares are monitored more frequently throughout gestation to catch any signs of placental insufficiency, weight loss, or metabolic instability early.
Postpartum care:
After foaling, the focus shifts to ensuring placental expulsion and guarding against uterine infections. Quick treatment is critical to protect the mare’s long-term reproductive health.
Common health interventions
Managing Cushing’s Disease (PPID):
Treatment with pergolide, combined with a low-sugar diet, helps manage insulin resistance and overall wellbeing. (McGowan et al., 2013)
Supporting joint health:
Supplements and injectables (like hyaluronic acid) help keep older mares mobile and comfortable – important for paddock movement and general health.
Treating uterine infections:
Older mares often need uterine lavage and antimicrobials between cycles to resolve infections and improve fertility outcomes.
Real-world perspective
While it’s easy to look at numbers on a vet report, the best breeders will tell you: a good older mare is worth the work.
She may not be the quickest to conceive, but with known form, proven production, and the right management, many produce exceptional offspring late into life.
Conclusion
Managing older mares in breeding isn’t about giving them “one last chance”, but working smarter: combining science, close monitoring, and tailored care. Challenges like declining fertility, inflammation, or systemic health issues are real, but they’re manageable.
With modern tools and experienced hands, older mares continue to play a valuable, productive role in Thoroughbred breeding programs.
