Can a Mare’s Personality Change After Her First Foal?

Dr. Nancy Diehl addresses a question about why a mare might respond differently to training after having her first foal.

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Can a Mare
Pregnancy hormones and then the presence of a foal at her side might temporarily change a mare's behavior. | Photo:
Q: My performance mare seemed to change after having a foal. Before the foal, she was hot and sensitive but straight forward to train. After the foal, when we put her back to work, she became moody, spooky, and stubborn. Can being used for breeding change a mare’s personality?

A: Can a mare’s personality change after being used for breeding? That is a great question and one I can’t answer definitively. Pregnancy hormones and then the presence of a foal at her side might temporarily change a mare’s behavior. I have not found any research on point here about long-term changes, particularly with regard to training and performance behavior.

The “common wisdom” is that breeding a mare will make her mellower, but lots of anecdotal reports out there go either way–yes, she changes, or no, she goes back to her old personality after the foal is weaned. But I have some thoughts and questions to consider that might help lead you to an answer about your mare’s apparent change in her behavior during training.

I am answering this under the assumption that your foal has been weaned. If not, it is possible your mare’s change in behavior is due to leaving her foal behind during her training sessions. Mares are highly individual in their anxiety when separated from their foals, even as the foal ages and they both appear more independent.

In any mare who has some kind of behavior change, we should always first consider disease of the reproductive tract. Certain ovarian tumors or persistent ovarian structures can definitely cause a behavior change. Uterine infections, even quite severe ones, might not cause any general physiologic or behavior changes, but that’s worth considering too. So you might want to have your veterinarian do a reproductive examination on your mare.

Past experiences can affect current behavior, and apparent personality changes could actually be just learned responses. So it’s worth thinking about your mare’s behavior in detail and how she was handled throughout the time she was being bred, pregnant, and had a foal at side. Were there any changes in who was handling the mare during pregnancy and after foaling? Could she have learned some undesirable behaviors from her interactions with other people? Was she an extremely protective mother? If so, perhaps she learned some behaviors to get people to leave her be, which she’s transferred effectively to her riding career.

Perhaps even a typical level of protectiveness has earned your mare some experience in attention and vigilance that translates to being spooky or stubborn. Consider your mare’s current environment. Perhaps now that your mare has experience with a stallion (if she was bred naturally) and having a foal at side, she might behave differently now if she is in proximity to stallions and foals. This might even vary with her estrous cycle.

There are also some simple changes that might have happened over the past year or two that you’ve probably thought of. Has your skill and experience changed? Do you have a new trainer or instructor who has different expectations of your mare or a different style of training? Has this mare’s career changed pre- and post-breeding? A mare coming off of a racing career might show quite dramatic changes in behavior over time with or without being bred. It’s possible your mare’s behavior change might just be coincident with another year or two in age and maturity.

I don’t think what we know about free-running mares helps much with your specific question. A mare’s affiliation with others in her group certainly changes after foaling, with her own foal, as well as her older foals if they are still in the group, generally becoming her closest frequent companions.  Mares in a natural breeding group don’t usually change their dominance status by virtue of having a foal. Their dominance status might change over time after many foals, but this might just be due to their being older and residing in the group longer.


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Prior to attending veterinary school, Dr. Nancy Diehl completed a master’s degree in animal science while studying stallion sexual behavior. Later, she completed a residency in large animal internal medicine at the University of Pennsylvania’s New Bolton Center and worked in equine practices in Missouri and Pennsylvania. Diehl also spent six years on faculty at Penn State, where she taught equine science and behavior courses and advised graduate students completing equine behavior research. Additionally, Diehl has co-authored scientific papers on stallion behavior, early intensive handling of foals, and feral horse contraception. Currently she is a practicing veterinarian in central Pennsylvania.

2 Responses

  1. I wish I could talk to the person who asked this question. Before my mare had her foal she was ever so good about having her feet trimmed. Since she has had her foal it has taken me about a year to convince her to let me clean out her feet. It got so bad that the trimmer has refused to trim her feet any more. In the end the trimmer gave up and I am now learning to trim her feet myself. I am however very lucky as she produced a lovely filly and I am sure one day we will manage to convince my mare to let me do her feet without any fuss any more.

  2. *sighs* I seriously have to shake my head when I read questions (and responses) like these. First let me state that I’ve been an equine keeper/steward for 45+ years to numerous equines and currently help care for 16 daily. Back in the latter 70’s I consulted in equine reproductive management which thankfully gave me further insight into both equine (and human) behaviors. The vocation I retired from was a consulting technical training specialist in the nuclear field so I am capable of objective reasoning based on observation and experience.

    This said, looking back, and forward YES breeding can and does have an effect on a mares behavior after the fact. Of course this varies by individual. What disappoints and frustrates me is that so few breeders (casual and ‘professional’) seem to accept the risks associated without complaint when things don’t go as they want them to. In this case I hope that this individual is grateful and pleased that both mare and foal went through the experience unscathed and work around their mares behavior/disposition changes. There are ALWAYS consequences for one’s choices and if one is not willing to accept worst case without complaint then perhaps it’s prudent to forego said desire. Choices and decisions should be made based on statistical ‘risk analysis’ that are based on objective criteria…

    ~”We tend to forget that happiness doesn’t come as a result of getting something we don’t have, but rather of recognizing and appreciating what we do have.” – Frederick Koenig~

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