Chasteberry, or Vitex agnus-castus, has been used by women for centuries for helping to smooth out hormones during menopause. The dried berry-like fruits of this small tree are tinctured for use.
In humans Chasteberry can help make irregular cycles more regular, it can help make you feel more grounded and bring about relief from a range of hormone-related problems like acne, water retention, improve digestion and calm frazzled nerves.
People have found that it can also help smooth out hormonal issues in horses. It is used in treating Cushing's disease and for reducing hormonal behaviour in some mares during oestrus. We also know people who have used it to help stop colts or geldings getting a bit 'uppity'. In humans it is known to be used by monks as an 'anti-aphrodisiac', so maybe a similar thing happens in horses!
The best way to administer it to your hormonal horse is to dilute a teaspoonful of tincture in at least the same amount of water. Put it in a syringe (without the needle!) and then gently squirt it into the corner of the horse's mouth. Give them this dose twice a day for up to five days.
Do not use Chasteberry on a mare that is in foal.