Learn the benefits and risks of magnesium for horses, including calming effects, gut health impacts, and correct supplementation for metabolic, behavioural and performance support.
Magnesium is one of the most commonly used supplements in horses, which when used appropriately, can be significantly beneficial. Yet often little consideration is given to important specifics around the use of this mineral. These generally overlooked nuances can help to determine how effective the magnesium is and if it is actually helpful or harmful to give your horse.
Magnesium plays many vital roles in the body. It is needed for over 300 enzymatic processes. From helping ‘wired’, reactive or anxious horses to reducing inflammation, supporting fertility, promoting bone health, metabolic function, and insulin regulation, magnesium has a wide range of applications.
Because magnesium is a naturally occurring nutrient, it is frequently assumed to be completely safe and free from side effects. Yet in reality, it isn’t quite this simple. Like many other supplements and nutrients, there are many factors which determine the safety and effectiveness of magnesium: how and what it is used for, the quantity of magnesium a horse is given, the duration of supplementation, the form of magnesium used, a horse’s overall diet and intake of other specific nutrients, exercise and activity levels, breed, sweat rate, any health conditions a horse may have, the state of its gastrointestinal health and any medications a horse is on.
If you’re already supplementing or considering using magnesium for your horse, here are some key things worth considering.
Not all magnesiums are created equal
Magnesium comes in a variety of forms, depending on what it’s bound to. This refers to the chemical structure of the magnesium, not just whether it is in liquid or powdered form. The most commonly used forms of magnesium (which also tend to be the cheapest forms of magnesium) in equine supplements include:
- Magnesium oxide
- Magnesium chloride
- Magnesium sulphate
Each of these forms differs in terms of absorption, bioavailability, and how they interact with the digestive system. Yet they are generally not the most clinically effective forms of magnesium to use.
This matters more than many people realise.
Magnesium can irritate the gut
Some forms of magnesium, particularly at higher doses can irritate the digestive tract.
Clinically, this may present in our horses as:
- loose and/or more frequent manure
- gassiness/excessive passing of wind
- changes in gut comfort and/or signs of mild colic
- worsening of existing digestive sensitivity
This is often dismissed or overlooked, especially if magnesium is being used for behavioural reasons.
Over-supplementation can disrupt the gut microbiome
High doses, poorly absorbed forms of magnesium or long-term over-supplementation may contribute to gut dysbiosis (an imbalance in gut bacteria). This can have wider consequences, including:
Magnesium can help to promote a healthy gut microbiome and reduce gastrointestinal-associated inflammation, but more is not always better.
- negative impacts on immune function
- altered nervous system function
- changes in neurotransmitter production and function
Our horses’ digestive systems can play a significant role in their behaviour, anxiety levels and learning capacity, thanks to the role of the gut-brain axis. Ironically, this means that excessive magnesium use may actually make some horses more reactive or sensitive, not less.
Magnesium can interfere with other essential nutrients, causing relative nutrient deficiencies
Magnesium doesn’t work in isolation. It interacts closely with other minerals including:
- calcium
- phosphorus
- zinc
Excess magnesium can interfere with the absorption and utilisation of these nutrients, which are critical for:
- bone strength and development
- proper neuromuscular function
- healthy immune function
- healthy nervous system function
- reducing oxidation and inflammation
- muscle, tendon and ligament health
Calcium and zinc in particular, play key roles in the synthesis and function of neurotransmitters such as:
- Dopamine
- Serotonin
- GABA
Imbalances in these neurotransmitters can directly influence behaviour, sensitivity, pain perception, reactivity, learning ability and response to training.
Magnesium and behaviour: not always a simple fix
Magnesium is often used to help calm or relax our horses, and in some cases, when used appropriately it can be most beneficial. When magnesium doesn’t help to address the underlying cause(s) of anxious or excitable behaviour however, the effects of supplementation will be minimal.
The effectiveness of magnesium supplementation will also be minimal and may compound behavioural issues if the delicate balances of other minerals are disrupted, magnesium is overused, poorly bioavailable forms of magnesium are employed, or the gut microbiome is negatively impacted. In these cases behavioural issues may actually worsen rather than improve.
It is important to remember that many things can contribute to adverse behaviour in our horses, and in the vast majority of cases, there are multiple causes at any one time, not just one single factor. Whilst diet, nutrient deficiencies and gut microbiome all play an important part, it would be remiss to overlooked issues such as pain, learned conditioning, side effects of other medications used (if applicable) and other underlying health issues. Supplemental magnesium will be of very limited benefit if the issues causing a horse’s poor behaviour are not properly addressed.
This is why a blanket approach to supplement with magnesium doesn’t always deliver consistent results.
Where magnesium can be highly beneficial
When used appropriately, magnesium can be valuable, particularly in horses with:
Metabolic Challenges
Magnesium plays a role in regulating blood glucose and insulin levels. It can be especially supportive in horses with:
- insulin resistance (IR) or insulin dysregulation (ID)
- equine metabolic syndrome (EMS)
- laminitis or at risk of laminitis
Increased Physical Demand
Horses lose magnesium through sweat, and in the case of broodmares, through their milk. Requirements may increase in:
- horses in intense workloads
- hot and/or humid climates
- lactating mares
- during travel
In these cases, intake may increase in the range of 1.5 to 2 times maintenance levels.
Diet still matters: natural sources of magnesium
Like many minerals, magnesium naturally occurs in feeds commonly given to our horses. Lucerne (alfalfa) hay is a useful natural source of magnesium. Fortified concentrate and balancer feeds have varying levels of magnesium.
However, it is not always quite as simple as relying on feed alone (or even, relying on nutritional information on a feed bag or product label).
Feeds or supplements which contain high levels of calcium (such as lucerne/alfalfa) can inhibit magnesium absorption to some degree. This highlights the importance of looking at the whole diet, not just individual nutrients or feed components, nor relying on feed programs or calculators alone.
Medications can change magnesium requirements
Many commonly used medications in horses can alter magnesium absorption, metabolism, or excretion, meaning their requirements may shift.
These include:
- corticosteroids
- proton pump inhibitors (the include the most commonly used ulcer medications which contain omeprazole)
- antibiotics
- non-steroidal anti-inflammatory drugs (NSAIDs)
- antihistamines
- clenbuterol (β2-agonists, which are often sold under names such as Claire Gel, Broncopulmin, Airway Gel, Ventipulmin, Equipulmin, etc).
If your horse is on medication, magnesium supplementation should always be considered more carefully. Dose, form, timing and duration of magnesium supplementation is crucial to take into account.
In summary: use magnesium strategically, not automatically
Magnesium is a powerful and valuable tool in equine nutrition and medicine, but it’s not without its limitations.
Used well, it can support:
- metabolic health
- muscle function
- nervous system balance and in turn, behaviour
- skeletal health
- fertility
- gastrointestinal (‘gut’) health
Used poorly, it can:
- disrupt gut health
- create mineral imbalances and relative nutrient deficiencies
- contribute to ongoing behavioural issues
- interfere with normal bone development and health
The key is not just whether your horse is supplemented with magnesium, but what their actual requirements for it are. The form of magnesium used to supplement, the reasons to supplement it, the duration of supplementation, factors which increase requirements or interfere with magnesium absorption and metabolism should all be taken into consideration.
Take home message
Good equine nutrition is never about using a single supplement in isolation. Assessing the unique needs of the individual horse in front of you is crucial.
Before supplementing magnesium, it’s always worth asking:
- does my horse actually need it? And if so, how much?
- is the diet balanced overall? And what role would supplemental magnesium potentially play in this?
- could there be deeper underlying causes contributing to the reasons which are prompting me to supplement magnesium?
The safest, most effective and sustainable results come from a thoughtful, tailored approach.
Camilla Whishaw is a highly regarded, experienced horsewoman and naturopath, helping to holistically treat and manage a broad range of equine health conditions and injuries, with a passion for mare and stallion fertility.
As a world-renowned practitioner, presenter, author, and consultant in the field of Equine Naturopathy, Camilla shares her knowledge through keynote presentations, interviews, lectures, panel sessions, and workshop training.
