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 obesity and insulin resistance) Chasteberry extracts improved liver function and decreased oxidative stress. 
- Reduced stress responses: Chasteberry extract decreased pituitary production of adrenocorticotropic hormone (ACTH) which might support normal cortisol levels 
- Improved thyroid function: 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 
- Supports healthy bones: It had an osteoprotective effect in castrated males, meaning that it helps to protects bone from physical damage or degeneration 
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: 
- 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.
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. 
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 is not approved 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 using chasteberry to improve symptoms before administering pergolide or in combination with pergolide.
Early vs. Advanced PPID
Chasteberry appears to be more beneficial 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. 
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. 
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: 
- Animals that had never received treatment and were given chasteberry alone for six months
- Animals that had never received treatment and were given chasteberry plus pergolide for six months
- 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.
Horses with PPID have pituitary glands which overproduce 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 but can be used as an adjunct therapy to support improvement of symptoms.
That being said, the main outward sign of elevated ACTH (excessive hair growth and failed shedding) was improved by Chasteberry. 
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.” 
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…” 
A common cause of mood problems in female horses is the oestrus cycle. Both breeding and non-breeding mares will experience changes in mood and behaviour related to hormonal fluctuations.
Changes in mood linked to the oestrus cycle can include: 
- Unpredictable behaviour
- Kicking out
- Lack of interest in other horses
- Changes in social behaviour
- Decline in performance
- Back soreness
- Loss of interest in food
- 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.
Effects on Progesterone
Chasteberry is purported to work for horses in a similar way as for women. According to equine herbalists, it works by raising progesterone levels which helps to relieve symptoms of PMS as well as other menstrual cycle abnormalities. 
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 stops reproductive cycles in horses and 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 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
- 1,8-cineole [eucalyptol]
- Iridoid glycosides
- Labdane- and cleradone- type
Mechanism of Action
In rats and other animals, chasteberry extract has been shown to stimulate dopamine receptors, increasing 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 progesterone levels.  The calming effect on moody mares is likely related to this shift towards higher progesterone levels.
In male mice, chasteberry extract also decreased LH, resulting in decreased testosterone levels. This might indicate that chasteberry calms aggressive stallions by decreasing testosterone. 
Anecdotal evidence also suggests chasteberry helps with cresty neck and irregular fat deposits in insulin-resistant horses. It may work by improving insulin sensitivity, but further studies are required to validate this hypothesis.
Chasteberry is safe to use in insulin-resistant horses and could improve fat distribution, glucose tolerance, and frequency of drinking (polydipsia) and frequency of urination (polyuria).
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 (1100 lb) horse is 5 to 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 pregnant or lactating. Studies in other mammals suggest it could cause lactation suppression.
Based on anecdotal reports, it can take several weeks to months for the effects of chasteberry to become noticeable.
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