I have a mare who has a habit of eating the other horses' manes. What is the cause of this, and how can I stop it?
—Cherity
Cherity, horses often groom each other by "scratching" the withers and necks of other horses with their teeth. This is normal behavior. However, as you have observed, the behavior can sometimes escalate to actually chewing the manes of other horses. One of the reasons this can occur is lack of enrichment and stimulation.
Try adding some enrichment options to your mare's daily routine. If she is in a pasture, spread her hay in small piles or have her eat from a hay saver that requires time and noodling around to get the hay out. Rolling treat dispensers and daily positive reinforcement training sessions are other options. Additionally, watch to see if there are particular times of day that your mare conducts the behavior—is it near feeding time, or maybe after a long turn-out? This will help you pinpoint the time of day for intervention.