Chasteberry is an herbal supplement that is used to support mood balance and hormone health in female and male horses.
The Chastetree berry (Vitex agnus-castus) plant is a shrub that grows in the Mediterranean and parts of Asia. The fruits and leaves contain active ingredients that influence hormonal balance in horses.
This herb is purported to support hypothalamus and pituitary function in horses with Cushing’s disease/PPID. Anecdotally, chasteberry is said to help make moody mares easier to handle and may have a calming effect on aggressive stallions or geldings.
Chasteberry is safe to use, with no reported side effects in horses. It is not recommended for pregnant mares because of potential effects on the reproductive system which have not been evaluated in pregnant animals. 
Mad Barn’s bulk Chasteberry Powder is made of pure dried chastetree berry fruit without any additional ingredients. It should be fed at a rate of 5-20 grams per day, increasing the serving size slowly to limit avoidance.
Why Use Chasteberry in Horses?
Chasteberry is primarily used in horses to enhance mood and improve behaviour. It is also said to have positive effects on:
- Metabolic health
- Energy levels
- Healthy coats
- Hormone regulation
- Muscle tone
- Aging and growth
In traditional medicine, Chasteberry extract (Vitex) was originally thought to promote chastity, hence its name. The dried fruit was used by monks to decrease sexual desire. You might also find it labelled under the name Monk’s pepper.
Today, it is commonly used to treat premenstrual syndrome (PMS) and menopause in women. It has been shown to lower prolactin levels which helps alleviate symptoms of reproductive cycling in women. 
Though the effects of this herb have not been well-researched in horses, it is growing in popularity due to a strong body of anecdotal evidence from veterinarians and horse owners who have seen positive transformations in their equine companions.
By increasing the ratio of progesterone to estrogen, chasteberry might help moody mares with behaviour issues that are related to being in season.
Horses with Equine Cushing’s Disease (Hyperadrenocorticism, Pituitary Pars Intermedia Dysfunction/PPID) often have elevated prolactin levels which contributes to infertility and enlarged udders.
Chasteberry will not cure or treat Cushing’s, but it can help support normal pituitary function and lower prolactin levels. This can improve fertility in horses and address symptoms of Cushing’s including helping hair shed out.
Benefits of Chasteberry in Horses
Chasteberry has been studied in horses with Cushing’s disease in which it showed the following six benefits: 
1) Improves shedding
Excess hair growth or lack of shedding, known as hirsutism, is one of the most obvious features of Cushing’s disease/PPID.
Chasteberry was shown to stimulate shedding, and support a healthier, shinier coat. This also led to a reduction in excessive sweating, making horses more comfortable and heat tolerant.
2) Reduces fatigue and improves energy levels
Chasteberry was found to reduce fatigue, support better energy levels and improve regulation of thyroid activity. The thyroid gland is a key regulator for the body, controlling metabolism and many other functions.
By lowering cortisol which is known to inhibit thyroid function, Chasteberry supports healthy thyroid function.
3) Supports mood and attitude
Horses with depression and low mood show improvements with Chasteberry, making them easier to handle and more cooperative.
By supporting hypothalamus and pituitary function, and lowering levels of the stress hormone cortisol, Chasteberry can support mental well-being and improve handling.
4) Supports hoof health
In horses with Cushing’s/PPID, chasteberry reduced incidence of laminitis and possibly improved laminitis pain. Chasteberry has been shown to improve glucose tolerance and insulin sensitivity in some horses with insulin resistance, a common contributing factor to laminitis.
The inflammation and weak hooves that are associated with laminitis is painful for horses. Chasteberry was shown to reduce signs of pain associated with laminitis.
5) Normalizes urination and drinking behaviour
Chasteberry was found to reduce frequency of urination (polyuria) and drinking (polydipsia). This suggests Chasteberry extract improves glucose tolerance.
When glucose is high in the body more is excreted in the urine, this draws a lot of water with it which increases frequency and volume of urination and stimulates thirst. By supporting normal glucose metabolism, Chasteberry minimizes these outward signs of high glucose levels
6) Supports normal fat distribution
Insulin resistance in horses can lead to abnormal fat deposits in the crest of the neck, tail head or prepuce and mammary regions.
By improving insulin sensitivity, Chasteberry can help support normal fat distribution.
Additional Positive Effects
Research suggest that chasteberry works by nutritionally supporting the normal function of the pituitary gland and endocrine system.
By supporting healthy pituitary function, chasteberry could have numerous beneficial effects.
The hypothalamus and pituitary gland are key parts of the brain that receive signals from the body and produce hormones to regulate a wide array of metabolic processes.
Research in other animals and humans suggests that extracts from the chasteberry shrub might have additional benefits which need to be assessed in horses including:
- Anti-inflammatory effects: In mice, extracts from the Chasteberry fruit inhibited inflammation and pain associated with inflammation 
- Anti-oxidant benefits: Flavonoids and phenol compounds in Chasteberry extracts are effective at neutralizing free radicals 
- Anti-aging: Chasteberry extract has been shown to improve some problems of aging including oxidative stress and female sex hormone deficiency 
- Improved liver function: In animals with fatty liver (a common feature of obesit