Clearing Uterine Fluid From Mares After Mating 

Expect fluid and inflammation in the uterus after breeding, especially in susceptible mares.
Old broodmare with foal, might have PMIE, might need help clearing uterine fluid
Older mares are more susceptible to PMIE, and correcting poor perineal conformation can help them get in foal. | Getty Images

Post-mating induced endometritis (PMIE) can be very frustrating. During her Burst Session presentation at the 2023 AAEP Convention, however, Melissa Prell, DVM, MS, Dipl. ACT, assured practitioners that clearing up the fluid is simply a matter of understanding the process. 

“The uterus will have a reaction in response to semen being deposited with the goal of that reaction to clear excess semen out,” said Prell, director at Peterson Smith Advanced Fertility Center, in Summerfield, Florida. “This reaction peaks eight hours after mating and should be completely resolved in 24 to 48 hours.”  

Mares Susceptible to PMIE

A small population of mares is considered “susceptible,” making them more prone to PMIE. These include: 

  • Older mares with saggy uteri hanging in the abdomen where fluid pools.  
  • Mares with poor uterine contractility that can’t expel fluid. 
  • Mares with impaired uterine immune defense.  

“The majority of the time you won’t know the mare is going to be a problem until it is too late, so we are stuck playing catch up after breeding,” Prell warned.  

How to Address Uterine Fluid in Mares

When faced with fluid prior to breeding, however, always start with the basics. Perform culture and cytology and treat accordingly. This could include antibiotics, agents that disrupt the potential biofilm, anti-mucolytics, uterine lavage, or ecbolics such as oxytocin to aid in uterine clearance.  

Lavaging a mare five to six hours post-insemination will help clear the excess semen and help mitigate the inflammatory response within the uterus.  

“By that point, the important semen is already in the oviduct so you’re not going to wash it away,” reminded Pell. 

Other ways to help clear fluid and quell inflammation include platelet-rich plasma, acupuncture, exercise/turnout, and immunoregulators such as Settle.  

“If a mare proves herself susceptible, then the best thing you can do is be prepared for the next cycle. Correct poor perineal conformation, limit the number of breedings/covers, or use artificial insemination to decrease the number of bacteria introduced to the uterus,” Pell said. 

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