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 hypothalamic and pituitary function in horses. 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 not recommended for pregnant and lactating mares or growing horses because of potential effects on the reproductive system which have not been evaluated in these animals. [2]

Mad Barn’s 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.

Chasteberry

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  • Supports mood balance
  • Supports hormone health
  • Pituitary function & fertility
  • Used in horses with Cushing's

Why Use Chasteberry in Horses?

Chasteberry is primarily used in horses to enhance mood and improve behaviour, by regulating some hormone levels.

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. [1]

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.

Chasteberry can support optimal levels of several reproductive hormones: luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen and progesterone. Therefore, chasteberry might help moody mares with behaviour issues that are related to being in season.

Chasteberry can alleviate some manifestations of Cushing’s Disease (PPID) but does not control hormonal output from the tumor. [17] There is also some evidence that it may interfere with the actions of pergolide, the drug commonly used to treat Cushing’s disease. [11]

Chasteberry supports healthy hormone balance and may help to maintain normal mood regulation and fertility.

Chasteberry Powder for Horses

Benefits of Chasteberry in Horses

Chasteberry has been studied in horses with Cushing’s disease in which it showed the following five benefits: [3][17]

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.

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, Chasteberry can support mental well-being and improve handling.

4) Supports horses with laminitis

In horses with Cushing’s/PPID, chasteberry reduced incidence of laminitis and possibly improved laminitis pain.

The hoof changes associated with laminitis are 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).

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.

Chasteberry also helps relieve the insulin resistance and ovarian abnormalities in PCOS – polycystic ovarian syndrome – in women. [18] Some mares with metabolic syndrome and hyperinsulinemia also exhibit ovarian and cycling abnormalities and therefore might benefit from chasteberry supplementation. [19][20]

Chasteberry activates opioid mu receptors in the brain, which may be partially responsible for the energizing and pain-relieving effects of chasteberry. [21][22] Narcotics, which also stimulate opioid receptors, have an energizing effect in horses.

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 [4]
  • Anti-oxidant benefits: Flavonoids and phenol compounds in Chasteberry extracts are effective at neutralizing free radicals [5]
  • Anti-aging: Chasteberry extract has been shown to improve some problems of aging including oxidative stress and female sex hormone deficiency [5]
  • Improved liver function: In animals with fatty liver (an occassional feature of obesity and insulin resistance) Chasteberry extracts improved liver function and decreased oxidative stress. [6]
  • Reduced stress responses: Chasteberry extract decreased pituitary production of adrenocorticotropic hormone (ACTH) which might support normal cortisol levels. [7] However, no effect on ACTH has been found in horses. [7][10][17]
  • Improved thyroid function: In mice, this plant extract increased thyroid stimulating hormone (TSH) secretion from the pituitary gland which increased thyroid hormone production. This could be beneficial in cases where thyroid function is impaired [7]
  • Supports healthy bones: It had an osteoprotective effect in castrated males, meaning that it helps to protect bone from physical damage or degeneration [8]
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Chasteberry Research in Horses

Research into the effectiveness of chasteberry for horses is limited. There have only been a small number of clinical studies that have examined the effects of this herb in equines. More studies are needed to evaluate the clinical efficacy of chasteberry for many of its purported health claims.

However, it has grown in popularity due to a large body of anecdotal evidence that it works. These include case reports and testimonials submitted by veterinarians and horse owners. In the following section, we will review some of the evidence for this herb.

Equine Cushing’s Disease

In one study, 25 horses and ponies diagnosed with Cushing’s disease were treated with chasteberry over a three-month period. The study used owner surveys and before-and-after photos to determine how horses responded to the treatment.

A daily dose of chasteberry for horses diagnosed with Cushing’s was found to: [3]

  • improve coat quality
  • improve energy levels
  • improve mood
  • reduce laminitis
  • reduce abnormal fat deposits

In an anecdotal case report, Dr. Eleanor Kellon, VMD of the ECIR Group describes 10 horses with Cushing’s disease showing improvements after several weeks on a commercial product containing Chasteberry extract. [13]

All 10 horses exhibited rapid shedding of the abnormal coat within 2-3 weeks of treatment. Horses that presented with low energy levels, depression, and pain due to laminitis before treatment showed improvement in these symptoms.

Several of the horses examined in this report also experienced improved insulin and glucose levels, suggesting benefits for metabolic health. The changes in insulin signalling were particularly noticeable in younger animals. [9]

However, it should be noted that this study and other older reports were written before we knew about the seasonal effects on PPID horses which could have influenced the results.

Chasteberry improved coat quality, mood, energy, metabolic health and laminitic pain in horses with Cushing’s/PPID.

Chasteberry vs. Pergolide

Pergolide is the pharmaceutical drug most commonly used in horses to treat symptoms of Equine Cushing’s Disease. Pergolide is an ergoline-based dopamine receptor agonist that is used in humans to treat Parkinson’s Disease.

Many horse owners seek out Chasteberry as a natural alternative to pergolide, but this herb should not be considered as a replacement for pergolide treatment.

If you suspect your horse is developing Cushing’s symptoms or has recently been diagnosed with early Cushing’s/PPID, speak with your veterinarian about appropriate use of supplements and medications.

Early vs. Advanced PPID

Chasteberry appears to be more beneficial for symptomatic relief in horses with early PPID, but may not be as effective as pergolide in horses in advanced stages of the disease.

One study showed no benefit of a commercial chasteberry product in PPID horses when it was compared to pergolide and showed deterioration in PPID symptoms in some horses. [10]

In this study, 14 horses with Cushing’s disease were given chasteberry extract daily for between two to six months. The horses were also treated with a high dose of pergolide either before or after receiving chasteberry.

In this comparative study, only one of the horses saw an improvement in their condition relative to treatment with pergolide.

These horses had advanced PPID, meaning that their symptoms has been present for a longer period of time or were more severe. Horses with advanced PPID are less likely to have symptoms resolved by chasteberry alone and require pergolide therapy to see significant clinical benefit.

The authors of this study acknowledged that the manufacturer did not provide details regarding chasteberry concentration or other active constituents and the investigators did not test the product. It is unclear how much was given and what other ingredients were in the product. [10]

Chasteberry is not as effective as Pergolide for advanced cases of PPID and should not be used as an alternative to this drug.

PPID Study with Horses and Ponies

In another study, a commercial chasteberry product was tested in 38 horses and ponies with PPID. The equids were divided into three groups: [11]

  1. Animals that had never received treatment and were given chasteberry alone for six months
  2. Animals that had never received treatment and were given chasteberry plus pergolide for six months
  3. Animals that were already on pergolide continued taking this drug alone for first 3 months and then were given pergolide plus chasteberry for the final 3 months

Blood tests and assessment of clinical symptoms were conducted before treatment, at 3 months and after 6 months. Chasteberry treatment alone improved the horses’ clinical scores after three months, which continued to six months.

The researchers observed normalization of the hair coat and behavioural changes with owners noting that the horses and ponies were more lively and alert. All horses showed improvement in Cushing’s symptoms as determined by a scoring system.

However, none of the existing reports on the effects of Chasteberry in PPID have followed the horses long term.

It has also been the experience of the 25 year old Equine Cushing’s and Insulin Resistance Group that horses treated only with Chasteberry eventually stop responding, at which time their symptoms are difficult to control even with pergolide. This is likely because the pituitary hypertrophy has been going unchecked. [13]

Chasteberry is not an alternative to pergolide at any stage of the disease because it does not control hormonal output from the pituitary.

Adrenocorticotropic Hormone

Horses with PPID have pituitary glands which overproduce hormones derived from POMC neurons, including beta-endorphin, alpha-melanocyte stimulating hormone, and adrenocorticotropic hormone (ACTH) resulting in many of the symptoms associated with this disease. The study results showed that chasteberry therapy alone did not improve ACTH levels. However, it has been established that pergolide does lower ACTH.

Therefore, chasteberry should not be considered a complete replacement therapy for pergolide and should not be used alongside pergolide because of possible interference with pergolide’s effectiveness. [18]

That being said, the main outward sign of PPID (excessive hair growth and failed shedding) was improved by Chasteberry. [11]

Chasteberry for Mood Balance

Chasteberry is popular for behavior modification and promoting a positive mood in both mares and stallions, but particularly in mares.

According to Kathleen Crandell, PhD, “Chasteberry is purportedly useful for making mares a little more cheerful and easier to handle.” [14]

The Holistic Horse states that chasteberry, “aids in counteracting irritability and unpredictability. It also helps horses feel more comfortable so that they will be more cooperative…” [15]

A common cause of mood problems in female horses is the estrus cycle. Both breeding and non-breeding mares will experience changes in mood and behaviour related to hormonal fluctuations.

Changes in mood linked to the estrus cycle can include: [16]

  • Aggression
  • Unpredictable behaviour
  • Kicking out
  • Stubbornness
  • Lack of interest in people
  • Changes in social behaviour
  • Decline in performance
  • Back soreness
  • Loss of interest in food
  • Girthiness
  • Lack of cooperation

Chasteberry is said to promote balanced behaviour by regulating hormone levels in horses.

It has been widely investigated in humans as a natural remedy for mood swings, depression and irritability linked to PMS. It is approved by the German Commission E for irregularities of the menstrual cycle, premenstrual complaints, and mastodynia.

Chasteberry appears to improve mood and handling behavior in mares by helping to maintain healthy hormone balance.

Effects on Sex Hormones

Chasteberry is purported to work for horses in a similar way as for women. Chasteberry enhances mood by being directly estrogenic but also improves levels of LH, FSH and progesterone. [16]

These claims are based on observations of horses that have been fed chasteberry products. Clinical studies have not been conducted to evaluate efficacy for changes in mood and will be needed to validate the claims made.

Veterinarians will sometimes prescribe Regu-mate for moody mares that are difficult to handle when in season. This synthetic progesterone product prevents mares from showing heat and experiencing behavioural issues.

However, it is expensive, difficult to handle and could suppress the immune system leading to infections.

Many mares on Regu-mate become dull and disinterested, with flagging performance. Many horse owners prefer to try chasteberry first before using Regu-mate for moody mares. Chasteberry will not prevent your mare from cycling but may improve her behaviour and outward signs of being in season.

How Does Chasteberry Work?

The fruits of the chasteberry shrub contain a number of active compounds and steroidal precursors that are believed to influence dopamine activity in the brain and sex hormone regulation.

Active ingredients include:

  • Essential oils
    • Limonene
    • Sabinene
    • 1,8-cineole [eucalyptol]
  • Iridoid glycosides
    • Agnoside
    • Aucubin
  • Diterpines
    • Labdane- and cleradone- type
    • Vitexilactone
    • Rotundifuran
  • Flavonoids
    • Apigenin
    • Castican
    • Orientin
    • Isovitexin

Mechanism of Action

In rats and other animals, chasteberry extract has been shown to stimulate dopamine receptors, mimicking increased activity of dopaminergic neurons.

This in turn decreases prolactin secretion by the pituitary gland. Prolactin is a hormone involved in lactation, but it also has a wide range of other functions in the body.

The decrease in prolactin activity results in increased production of luteinizing hormone (LH) by the ovaries as well as increased levels of follicle-stimulating hormone (FSH).

Higher levels of FSH subsequently results in increased estrogen levels. [5]

In male mice, high dose chasteberry extract also decreased LH, resulting in decreased testosterone levels. This might indicate that chasteberry calms aggressive stallions by decreasing testosterone. [12]

Chasteberry contains a number of active ingredients that influence dopamine, LH, FSH, and TSH and from there affects the sex hormones and thyroid hormone.

How to Use Chasteberry in Horses

The correct dosage of chasteberry depends on the form of the herb being used, the condition of your horse, bodyweight and the reasons for feeding this ingredient.

Some products may be more concentrated than others and may require a different dosage per day. Follow the feeding directions provided by the manufacturer of the specific product you are using.

If you are using dried ground chasteberry fruit, the average feeding rate for a 500 kg (1,100 lb) horse is 10 grams per day, but can range between 5 and 20 grams per day. It is not recommended to exceed 20 grams per day, unless under the direction of a qualified equine nutritionist or veterinarian.

We recommend starting at 5 grams per day and increasing the dosage until the desired result is achieved. You can read more about how to introduce a new supplement to your horse here.

Mad Barn’s bulk Chasteberry powder contains pure dried chaste tree fruit extract with no other additives. It provides a high-quality active ingredient in a palatable form.

Chasteberry should not be used in horses that are immature, pregnant or lactating. It should be avoided in stallions during the breeding season. Studies in other mammals suggest it could cause lactation suppression, although this effect is dose-dependent.

Based on anecdotal reports, it can take several weeks to months for the effects of chasteberry to become noticeable.

The typical chasteberry dose for a mature horse is 5 to 20 grams per day. This supplement should not be used for breeding stallions, pregnant or lactating horses, or growing horses.

Chasteberry

5 stars
87%
4 stars
4%
3 stars
5%
2 stars
2%
1 star
1%

Learn More

  • Supports mood balance
  • Supports hormone health
  • Pituitary function & fertility
  • Used in horses with Cushing's

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References

  1. Seidlova-Wuttke, D. and Wuttke, W.The premenstrual syndrome, premenstrual mastodynia, fibrocystic mastopathy and infertility have often common roots: effects of extracts of chasteberry (Vitex agnus castus) as a solution. Clinical Phytoscience. 2017.
  2. Harman, JoyceThe toxicology of herbs in equine practice. Clin Tech Equine Pract. 2002.
  3. Self, Hilary Materia Medica. Veterinary Herbal Medicine. 2007.
  4. Ramezani, M. et al Antinociceptive and Anti-inflammatory Effects of Hydroalcohol Extract of Vitex agnus castus Fruit. World Academy of Science, Engineering and Technology. 2010.
  5. Ahangarpour, Akram et al. Effects of Vitex agnus-castus fruit on sex hormones and antioxidant indices in a d-galactose-induced aging female mouse model. J Chinese Med Assoc. 2016.
  6. Moreno, FM et al. Vitex agnus-castus L. (Verbenaceae) Improves the Liver Lipid Metabolism and Redox State of Ovariectomized Rats. Hindawi. 2015.
  7. Sosic-Jurjevic, Branka et al. Functional morphology of pituitary -thyroid and -adrenocortical axes in middle-aged male rats treated with Vitex agnus castus essential oil. Acta Histochemica. 2016.
  8. Boeckhoff, Sehmisch et al. Vitex agnus castus as prophylaxis for osteopenia after orchidectomy in rats compared with estradiol and testosterone supplementation. USDA. 2009.
  9. Herbal Offers Hope For Cushing`s Syndrome. Equiisearch. 2017.
  10. Beech, Jill et al. Comparison of Vitex agnus castus Extract and Pergolide in Treatment of Equine Cushing’s Syndrome. Medicine II. 2001.
  11. Bradaric, Zrinjka et al. Use of the chasteberry preparation Corticosal for the treatment of pituitary pars intermedia dysfunction in horses. Pferdeheilkunde. 2013.
  12. Nasri, Sima et al. The effects of Vitex agnus castus extract and its interaction with dopaminergic system on LH and testosterone in male mice. Pak J Biol Sci. 2007.
  13. Kellon, E.M. Treatment of PPID. Accessed December 4, 2023.
  14. Kentucky Equine Research. Chasteberry For Mare Behavior? 2016.
  15. The Holistic Horse. Holistic Horse Organic ChasteBerry Hormone/Mood Balance Riding Warehouse.
  16. Dietz, B.M. et al. Botanicals and Their Bioactive Phytochemicals for Women’s Health. Pharmacol Rev. 2016 .
  17. Eustace, R. Equine metabolic syndrome and Cushing’s disease clinical trial. Vet Rec. 2008.
  18. Feyzollahi, Z. et al. Effect of Vitex agnus-castus ethanolic extract on hypothalamic KISS-1 gene expression in a rat model of polycystic ovary syndrome. Avicenna J Phytomed. 2021.
  19. Sessions-Bresnahan, D.R. and Carnevale, E.M. The effect of equine metabolic syndrome on the ovarian follicular environment. J Anim Sci. 2014.
  20. Sessions, D.R. et al. Development of a model for inducing transient insulin resistance in the mare: preliminary implications regarding the estrous cycle. J Anim Sci. 2004.
  21. Webster, D.E. et al. Opioidergic mechanisms underlying the actions of Vitex agnus-castus L. Biochem Pharmacol. 2011.
  22. Webster, D.E. et al. Activation of the mu-opiate receptor by Vitex agnus-castus methanol extracts: implication for its use in PMS. J Ethnopharmacol. 2006 .