Optim Equine Hormonal-Mares-&-Vitex-(AKA-ChasteberryChaste-tree)

Hormonal Mares & Vitex (AKA Chasteberry/Chaste tree).

During warmer weather and longer daylight hours, most mares and older fillies will cycle on a regular basis. For some fillies and mares this can bring challenges with both behaviour and performance.

A commonly used ‘natural’ supplement for ‘marey’ mares is the herb Vitex agnes castus (commonly referred to as Vitex, Chasteberry or Chaste tree).

During the estrus phase of a mare’s oestrus cycle (the time when a mare is ‘in season’), oestrogen levels peak- which can cause behavioural changes and increased sensitivity in our mares and fillies.

Vitex is an herb which can help to increase progesterone levels. Increasing progesterone levels can help to counter some of the signs and symptoms associated with excessively high oestrogen levels. Yet this herb definitely isn’t suitable for all ‘marey’ mares and fillies and can actually make behavioural issues worse.

Like many herbs, Vitex has more than one therapeutic action. In addition to modulating progesterone levels, it has dopaminergic actions: it increases the levels of the neurotransmitter dopamine. Dopamine is a stimulant neurotransmitter, and whilst it is common to see horses in clinical practice with low dopamine levels, there are also horses who have naturally higher dopamine levels. Those with high dopamine levels can demonstrate behaviours of irritability, hyperactivity, hypersensitivity and/or aggression.

Giving vitex to mares who already have high dopamine levels can make the whole problem worse. In clinical practice, vitex is rarely an herb I use in cases of hormonal mares and fillies.

Appropriately prescribed herbal medicines can be incredibly valuable, but understanding their totality of pharmacological actions is crucial to ensure we help our horses and not make a problem worse. It’s also an important reminder that herbal medicines are best prescribed by a suitably qualified and experienced practitioner- not just purchased online or off the shop shelf.

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