Marish Behavior: What Causes it?

No longer defensive, Sapphire enjoyed an ear rub

Sexually related behaviors such as flirting, squirting, winking, or squealing are caused by LUST, one of the 7 core emotions found in all mammals. LUST exists to promote survival of the species, so it naturally has a strong influence on a mare. Other behaviors often labeled “marish” include impatience, touchiness, defensiveness, and aggression. These have multiple possible causes. The first 3 are described by Dr. Sue McDonnell based on evaluations of horses referred to the University of Pennsylvania’s New Bolton Center. The 4th is based on owners' observations.
1. Pain related to estrus This behavior is cyclical, subsiding in winter months when mares stop cycling. Some medications or supplements might help, but any punitive reaction is likely to increase the mare’s stress and provoke more defensive behavior. Sometimes the best we can do is minimize the behavior by responding calmly instead of punitively, as described below in "Sapphire’s Story".
2. Pain from non-estrus related causes Behavior that is on-going is unlikely to be estrus-related. It could signify anything from ulcers to tumors to orthopedic problems, and should be evaluated by a veterinarian. One might wonder how many mares have pain that is overlooked because their pain-related behavior is falsely attributed to being “nasty”, “bitchy”, or any of the other negative terms often applied to mares. See "Hormones or Behavior Problem?" below for a veterinarian's guidance on how to tell the difference.
3. The way a mare is handled Two common myths routinely prompt humans to behave in ways that provoke unwanted behavior. One myth is that horses want to be dominant. They don’t; they want to feel safe. The other myth is that horses are supposed to respect our personal space, but we don’t need to respect theirs. Having people invade their space and behave dominantly toward them is a recipe for behavior that people call aggression, but is self-defense from a horse’s point of view. Details and references in these articles: (There are additional references at the end of this article)
Do Horses Really Want to Be Dominant?
Personal Space: Why the Double Standard?
4. Diet It is widely recognized that rich spring grass can cause problem behaviors in otherwise well-behaved horses, demonstrating that diet does indeed impact behavior. Some people have reported that with diet changes they hardly know their mares are in season. One type of diet change involved going to a low sugar / low carb diet. The other is eliminating legumes such as clover, soy, alfalfa, or lucerne. These are high in phytoestrogens, which have been shown to cause behavior changes in other species. Soy, especially high in phytoestrogens, is a commonly used protein in horse feed. More details and references in this article:
Can Food Make My Horse Behave Badly?

Sapphire’s Story Sapphire, our first mare, was an example of “marish” behavior provoked by faulty handling. She was variously described as a “boss mare", “quintessential dominant mare", and "hell on wheels". She scared people everywhere she lived. Anticipating “dominant” behavior from her, people were overly assertive with her, creating a vicious circle that became a self-fulfilling prophecy. Her threatening, "marish" behavior stopped completely when I stopped trying to show her I was boss. Instead I became her Protector Leader, focused on making her feel safe with me. (Protector Leadership is explained in detail in my book What Horses Really Want: Unlocking the Secrets to Trust, Cooperation, and Reliability.) I handled her gently, asking quietly for what I wanted, and giving her time to comply. I never changed what I asked, only how I asked. I never lowered my standards; I was just passively persistent instead of pushy. Rarely did I have to ask twice. She became a different horse; calm, cooperative, and relaxed. That was when I finally realized that under the drama she was anxious and sensitive. When people stopped triggering her anxiety, her true, sweet personality came out. The only drama that remained was her LUST-related behavior around strange geldings. Not all mares will change as dramatically as Sapphire did, but any improvement in behavior reduces everyone’s stress level, while increasing safety and cooperation. If this sounds too easy, here’s why. We aren’t training; we assume your horse is already trained. We are working with emotions. Instead of making the horse feel anxious, we want to make her feel safe. This really can be as simple as changing the way you relate to her. For mares whose heat cycles make them (and everyone around them) feel miserable, consider the sympathy and TLC you would want for yourself instead of fighting the behavior. One person described her own “TLC Protocol” for those days like this: Low stress riding or groundwork followed by a gentle massage. Is this letting a horse “get away” with something? No. It is realistic acceptance that you can’t “fix” this problem. You can only choose to increase everyone’s stress by fighting it, or earn your horse’s trust and devotion by showing you respect her feelings.

Hormones or Behavior Problem? If you are unsure whether behavior is related to hormone cycles, this is the advice of Peter Sheerin, DVM. “If it is related to the estrous cycle it should be happening every 21 days or so. I usually advise clients to start writing it on a calendar. And if the bad behavior continues in winter, it’s likely not related to the reproductive cycles.” Also consider the specific behavior, advises Dr. Sheerin. “Many mares, when they are in pain or angry, may urinate and swish their tails repeatedly, and people think they are in heat,” he says. “The posture and presentation of a mare that is urinating when she is in heat is different from a mare that is upset. The mare in heat will squat, with tail raised, and pass a little urine and may also ‘wink’ the clitoris.” An angry mare, in contrast usually swings her tail like a windmill or clamps her tail. She also passes much more urine.

References:
Heather Smith Thomas, “Mares Behaving Badly: Is it Estrus or Something Else?” The Horse, April 16, 2019 https://thehorse.com/19902/mares-behaving-badly-is-it-estrus-or-something-else/
Alexandra Beckstett, “Behavior Problems in Mares: Ovaries Aren’t Always to Blame”, The Horse, February 2, 2018 https://thehorse.com/139452/behavior-problems-in-mares-ovaries-arent-always-to-blame/
Christa Leste-Lasserre, “Researchers Develop Subjective Equine Personality Test”, The Horse, June 13, 2013 http://www.thehorse.com/articles/32036/researchers-develop-subjective-equine-personality-test
Christa Leste-Lasserre, “Study: Many Riders Don’t Groom Horses Properly or Safely,” The Horse (on-line) Nov 3, 2017 http://www.thehorse.com/articles/39871/study-many-riders-dont-groom-horses-properly-or-safely?utm_source=Newsletter&utm_medium=health-news&utm_campaign=11-07-2017

Feral Chincoteague mares share a gentle greeting

Are mares generally less tolerant of certain human behaviors than geldings or stallions are? The dynamics of feral herd behavior suggest that is possible. ”Marish” Mares and personal Space .