But my horse is a mare. Thank you so much. Depending where you live, this usually means during late spring, summer and early fall. Each mare is so different, just like women, about how they express their heat. Not an official term or syndrome, but you get the idea.
Some mares are grouchy just before estrus, some during and some after.
One of my mares behaves almost like a gelding. The others are more normal in their expression - not a big behavioral change. Now that it is winter, make note of your mare's anestrus behavior - that refers to the time period when her reproductive system is quiet or shut down for the winter, she is not cycling. Then as spring approaches, jot notes on a calendar. You might notice that a pattern emerges of days when your mare is sweet, cooperative and easy to work with and other days when she is impatient, preoccupied with something other than what you are doing with her, or downright grouchy and mean.