Why are my non-pregnant mare’s teats swollen – why is she lactating?
There are a few reasons why a non-pregnant mare can have enlarged or swollen teats and may even have clear to white liquid that can be drawn from them:
– Clover or other estrogenic plants – usually causes no problems, often comes on during summer pasture time and goes away during winter
– Cushing’s Disease in older mares – usually causes no problems but should be tested/treated for PPID
– Hormonal changes during transitional heat cycles
These causes noted above result in relatively equal, non-painful, not warm swellings of the teats. Do NOT milk out the mares as this may trigger continued lactation.
——————————————————————–
– Mastitis
– Abscess near the udder – possibly caused by Pigeon Fever or C. pseudotuberculosis
– Trauma to the udder
– Tumors
These causes noted above usually result in unevenly swollen, +/- painful, hot to the touch teats. You may find that the liquid in the teats is yellow to bloody. These cases should be seen by a veterinarian as soon as possible. Take your horse’s temp and record it for the veterinarian.
————————————————————————
If your mare has been exposed to a stallion – even if through a fence, consider pregnancy as a cause of lactation or swollen udders.
If your mare is pregnant and is not within the last few weeks of pregnancy and the teats have bagged up and/or are dripping milk, please have your vet examine the mare as soon as possible to rule out placentitis.
**The Vet Corner groups encourage members to establish a relationship with their local veterinarian, don’t wait until an emergency.**
© 2014-2025 Rural Veterinary Outreach. All Rights Reserved.
RVO Vet Corner Files 