Why Is My Horse Producing Milk? Causes and When to Call
By Dr. Zubair Khalid, DVM, MS, PhD ·
Why is my horse producing milk? If your mare is pregnant or recently foaled, milk production is expected and normal. If she is not pregnant and has never had a foal, or if she has been dry for months, milk or a milky discharge from the udder is a sign that something has changed in her hormone balance and she needs a veterinary exam. This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- A mare normally produces milk only around foaling and while nursing a foal, so milk in a non-pregnant, non-nursing mare is abnormal until proven otherwise.
- The most common cause in middle-aged and older mares is equine Cushing's disease (pituitary pars intermedia dysfunction, or PPID), which raises prolactin and can trigger lactation.
- Other causes include a recent pregnancy loss, an ovarian or hormonal problem, mastitis, and some medications.
- Do not milk her out or massage the udder, because that stimulates more milk and can introduce infection.
- Call your veterinarian for an exam and bloodwork, and treat it as an emergency if the udder is hot, hard, painful, or she has a fever or is not eating.
What Milk Production in a Mare Looks Like and What Is Normal
A mare's udder (mammary gland) sits between the hind legs, just in front of the rear legs. When she is close to foaling, the udder fills and may drip milk or a waxy, honey-colored fluid called colostrum. After foaling, she produces milk for her foal, and production tapers as the foal weans. That is the normal pattern.
Milk composition changes over lactation. In one study of mares on pasture, milk from late lactation had higher protein, lactose, and total nutrient levels, while early-lactation milk had higher sugar content and acidity [1]. Milk yield and composition also shift with the mare's age and how many foals she has had [1][2]. None of this matters much for a non-pregnant mare, but it explains why a mare who foaled months ago may still have a small amount of secretion.
So, do horses produce milk? Yes, but only as part of a pregnancy and nursing cycle. Do horses make milk without a foal? Sometimes, and that is the situation this article is about. Do horses drink milk? Foals do, from their dam. Adult horses do not need milk and should not be given cow's milk.
The key question is whether your mare is pregnant, recently foaled, or neither. If she is neither and her udder is enlarged or leaking, keep reading.
Why Is My Horse Producing Milk? The Main Causes
Equine Cushing's Disease (PPID)
This is the most common reason a non-pregnant mare starts producing milk. PPID affects the pituitary gland at the base of the brain. The gland enlarges and overproduces hormones, including prolactin, the hormone that drives milk production. Mares with PPID are usually middle-aged or older. Along with a bagged-up udder, you may notice a long, curly coat that does not shed, muscle loss along the topline, a pot belly, and increased drinking and urination. PPID is manageable with medication and monitoring, but it needs a diagnosis first.
Recent Pregnancy or Pregnancy Loss
A mare who was bred and lost the pregnancy early may still have a hormonally active udder for days to weeks. A mare who foaled and lost her foal will continue to produce milk until she dries up. If you do not know whether your mare was exposed to a stallion, assume pregnancy is possible until your veterinarian checks her.
Ovarian and Hormonal Abnormalities
Ovarian tumors and other hormonal imbalances can alter the mare's cycle and, in some cases, cause udder development. These are less common than PPID but are part of the differential list your veterinarian will consider. Reproductive problems are common in mares overall. In one study of Kazakh and Mugalzhar mares, infertility was found in 13.8 to 25.0 percent of mares, with ovarian disease accounting for 19.6 to 43.4 percent of infertile cases [3]. That does not mean every mare with milk has an ovarian problem, but it shows how often reproductive issues show up.
Mastitis
Mastitis is an infection of the mammary gland. The udder becomes hot, swollen, and painful, and the milk or discharge may look thick, clotted, or bloody. A mare with mastitis may resist handling, kick when you approach the udder, or act dull. This is a same-day veterinary problem.
Medications and Other Causes
Some drugs can raise prolactin or affect hormones. If your mare started a new medication and then developed an udder, tell your veterinarian. Other rare causes include liver disease and tumors that produce hormones. Your veterinarian will sort through these with a physical exam and lab work.
Cause Table
| Cause | Typical clues | How urgent |
|---|---|---|
| Equine Cushing's disease (PPID) | Older mare, long curly coat, muscle loss, pot belly, increased drinking, udder fills without pregnancy | Routine visit, but sooner if she is losing weight or lame |
| Recent pregnancy or pregnancy loss | Bred in the past year, no foal now, udder developed after breeding | Routine visit to confirm pregnancy status |
| Ovarian or hormonal problem | Irregular or absent heat cycles, behavioral changes, udder development | Routine visit with reproductive exam |
| Mastitis | Hot, hard, painful udder, abnormal discharge, fever, dull attitude | Same day, emergency if she is systemically ill |
| Medication effect | Udder developed after starting a drug | Call your veterinarian before stopping the drug |
If your mare is also losing weight or has a poor appetite, that combination deserves prompt attention. The same principle applies across species, and you can read more about how appetite and weight loss signal underlying disease in Why Is My Dog Losing Weight?.
Red Flags That Make It an Emergency
Call your veterinarian right away, or use an emergency service, if you see any of these:
- The udder is hot, hard, swollen, or painful to touch.
- The discharge is bloody, foul-smelling, or thick like pus.
- Your mare has a fever, is not eating, or is dull and depressed.
- She is lame on a hind leg or reluctant to walk.
- She is straining, lying down more than usual, or showing signs of colic.
- She is a broodmare close to foaling and has a sudden change in udder or discharge.
Mastitis can become severe quickly, and a mare with a painful udder may also be difficult to handle safely. Do not put yourself at risk by trying to examine or treat the udder alone.
Safe Things You Can Do at Home While You Wait
- Do not milk her out. Hand-milking or massaging the udder stimulates more milk production and can push bacteria into the teat canal.
- Keep the udder clean and dry. Gently wipe away drips with a clean cloth if the skin is irritated, then dry the area.
- Watch for changes. Note the size of the udder, the color and consistency of any discharge, and whether she seems painful.
- Check her attitude and appetite twice a day. Write down what you see so you can give your veterinarian accurate information.
- Do not start or stop any medication on your own. Some drugs affect hormones, and stopping them abruptly can cause problems.
- Keep her away from stallions if pregnancy is possible, and note any heat behavior.
- Take photos of the udder and discharge if it is safe to do so. Photos help your veterinarian decide how soon she needs to be seen.
If your mare is dribbling milk and also drooling or having trouble eating, that is a separate problem worth mentioning to your veterinarian. Drooling has many causes, and you can read about how it is evaluated in Why Is My Dog Drooling?.
What Your Veterinarian Will Check and Test
Your veterinarian will start with a full physical exam, including the udder, teats, and the milk itself. They will check your mare's body condition, coat, hooves, and attitude, and they will ask about breeding history, recent foaling, medications, and when the udder first appeared.
Bloodwork is usually the next step. For PPID, the veterinarian may run a resting ACTH level or a dynamic test such as the thyrotropin-releasing hormone stimulation test. They may also check for insulin dysregulation, which often goes along with PPID. A complete blood count and chemistry panel help rule out infection, liver disease, and other problems.
If pregnancy is possible, the veterinarian will check her reproductive tract, often with ultrasound. They may also examine the ovaries and uterus to look for tumors or infection. If the udder is abnormal, they may culture the milk to identify bacteria and choose the right antibiotic. They will calculate any drug dose from your mare's weight and health, so never use a dose from another horse or from the internet.
For context on how the mammary gland works and how milk release is controlled, the biology is similar across species. You can read a technical overview in Bovine Mammary Gland Physiology: Lactogenesis and Milk Ejection. The same principles of hormone-driven milk production apply to your mare.
Prevention and Monitoring
There is no sure way to prevent every case of abnormal lactation, but you can lower the risk and catch problems early.
- Track your mare's cycle and breeding dates. Knowing whether pregnancy is possible makes the diagnosis much faster.
- Weigh or body condition score your mare monthly. Unexplained weight loss or gain is an early clue.
- Watch for coat changes. A long, curly coat that does not shed is a classic PPID sign in older horses.
- Schedule annual wellness exams for mares over 15. Early PPID detection makes management easier.
- Keep a simple log of udder changes, heat cycles, and appetite. Bring it to your appointment.
- If your mare is on medication, ask your veterinarian about hormonal side effects before you worry.
If your mare is pregnant and you are preparing for foaling, know the signs of a difficult birth. The same principles of recognizing dystocia and acting fast apply across species, and you can read more in Dystocia in Cattle: Causes, Diagnosis, and Management.
Limitations and When to Contact a Veterinarian
This article cannot tell you what is causing your mare's milk production. Only a veterinarian who examines her can do that. Individual cases need a veterinarian, and the timing depends on what you see.
Contact your veterinarian the same day if the udder is hot, hard, or painful, if the discharge looks abnormal, if she has a fever, or if she is not eating normally.
Treat it as an emergency now if she is dull and depressed, has a high fever, is straining or showing colic signs, is lame on a hind leg, or if the udder is severely swollen and she will not let you near it.
Schedule a routine visit if the udder is soft and not painful, she is acting normal, and you simply noticed milk or udder development in a mare who is not pregnant. Even in that case, do not wait months. Hormonal causes like PPID are easier to manage when caught early.
Frequently Asked Questions
Can a mare produce milk without being pregnant?
Yes, and it is always worth investigating. The most common cause is equine Cushing's disease, which raises prolactin and triggers udder development in older mares. Other causes include a recent pregnancy loss, ovarian problems, mastitis, and some medications.
Is it normal for an older mare to have a full udder?
No, a full udder in an older mare who is not pregnant or nursing is not normal. It often points to PPID, especially if she also has a long coat, muscle loss, or a pot belly. Your veterinarian can test for it with bloodwork.
Should I milk out my mare to relieve the pressure?
No. Milking her out tells her body to make more milk and can introduce bacteria into the teat. Keep the udder clean and dry, and let your veterinarian decide on treatment. If the udder is painful or hot, call right away.
How long does a mare produce milk after foaling?
A mare produces milk for as long as her foal nurses, and production tapers as the foal eats more solid food. If she loses her foal, she will keep producing milk until she dries up, which can take days to weeks. Your veterinarian can advise you on managing that process.
Can milk production in a mare be treated?
It depends on the cause. PPID is managed with medication and monitoring, mastitis is treated with antibiotics chosen from a milk culture, and pregnancy-related milk usually resolves on its own. Your veterinarian will calculate any dose from your mare's weight and health, so never use a dose meant for another horse.
Related Articles
- Dystocia in Cattle: Causes, Diagnosis, and Management
- Why Does My Dog Have Bad Gas?
- Why Is My Dog Drooling?
- Why Is My Dog Losing Weight?
- Bovine Mammary Gland Physiology: Lactogenesis and Milk Ejection
- Why Is My Dog So Itchy?
References
- The Effects of the Lactation Period, Mare Age, and Foaling on the Chemical and Physical Composition of Milk from Kazakh Mares Kept Under Natural Pasture Conditions. Animals : an open access journal from MDPI, 2025.
- Growth Performance, Milk Productivity, Productive Longevity, and Milk Composition of Mugalzhar Horses. Animals : an open access journal from MDPI, 2026.
- Effective methods of horse reproduction in the production of mare's milk. Brazilian journal of biology = Revista brasleira de biologia, 2026.