Magnesium oxide is a concentrated magnesium supplement for horses that supports normal muscle function, metabolic health, and a balanced stress response. Magnesium is an essential mineral involved in hundreds of enzymatic reactions in the horse’s body. It plays a role in muscle contraction and relaxation, nerve signaling, bone health, and electrolyte balance.
Supports normal muscle contraction, relaxation, and post-exercise care
Helps maintain healthy nerve signaling in tense or reactive horses
Contributes to more focused and responsive behavior during work
Supports normal glucose metabolism and metabolic health
The magnesium supplement has been awesome for my mare. She is more relaxed in her muscles and is more comfortable during her heat cycles.
Hannah Curtis
Verified Customer
This by far is the most effective Magnesium supplement I have used to date. His overall demeanor seemed more content and less erratic when things got busy in the barn.
April MacLean
Verified Customer
My 5 year old mare has been on Mad Barn’s magnesium oxide for just over a month. Trainer says it is helping her to not be so reactive/sensitive to every little thing.
Linnea Epstein
Verified Customer
I love all the products I get from Mad Barn. The Magnesium has really helped my rapidly growing two year old filly with her growing pains!
Tracey Harnish
Verified Customer
Both of my horses are elderly... Making sure they get plenty of magnesium helps with everything; soreness, mood, digestion... mad barn's high quality, affordable mag ox is a staple
Rachel Hackett
Verified Customer
Our body worker recommended Dolly be put on a Magnesium supplement to help with her tight muscles and I can already see a difference in her since starting the Magnesium Oxide.
Lora Muse
Verified Customer
We also added magnesium to help with his anxiety and let me tell you it was like a new horse and a totally different personality! He was laid back and affectionate.
Sara Duncan
Verified Customer
This product has been a game changer for my anxious OTTB. It was a last ditch effort to try and help him through some of his anxiety and it made the biggest difference...
Samantha Bruggink
Verified Customer
I have been feeding my mare this for about 2 years. It has made a world of difference in her— she is much quieter and less agitated (charging, biting) with her pasture mates.
Aubrey Isaacson
Verified Customer
I started my gelding on Magnesium Oxide because he's levels was making him very nervous and just a flight risk to ride... hands down great folks, great product and amazing prices.
Cassondra Akers
Verified Customer
My Arabian always seemed to tight in his hamstrings... Since I started adding magnesium to his diet his muscles are much better and this shows in his performance.
Kaaren YoungLebert
Verified Customer
This is a great product. I’m ready to refill my stock! My horse is back to being sane, has no residual soreness, and has his thinking cap on when working!
Melissa Barber
Verified Customer
This is the first time I have tried Magnesium for my mare and I am really pleased with the results. Shopping on the Madbarn website is always a pleasure too.
Debbie House
Verified Customer
... [Magnesium Oxide] has been literally a game changer. Especially in my 2 yr old mare who had some mood swings so to speak. Within days she is back to being her happy self.
Tara Baldwin
Verified Customer
Magnesium has been the only thing that has helped to calm my overly anxious gelding. I love the confidence I am able to have when purchasing from Mad Barn...
Haylee Kroeger
Verified Customer
I have been using this for about 2 years now and absolutely love what it does for my horses. ...Now he is calmer and easier to handle and we actually enjoy our time riding.
Gwen Sanche
Verified Customer
I have an OTTB mare who has EPM and the magnesium helps her muscle soreness tremendously. Without it I’m not able to groom her but when she’s on it I can touch her all over
Alisha
Verified Customer
We stand behind our products to provide the best nutrition for your horse. No fillers, just research-backed ingredients. If your horse doesn't love this product, our Customer Happiness team is here to help or give you a refund guaranteed.
Magnesium Oxide
Magnesium is an essential macro-mineral involved in hundreds of enzymatic reactions that regulate energy metabolism, nerve transmission, and muscle contraction. It supports bone integrity, cardiovascular function, and normal insulin sensitivity in horses.
In muscle tissue, magnesium contributes to relaxation following contraction, helping to maintain normal muscle tone and reducing the risk of cramping or tightness. It also plays a role in maintaining a calm temperament by supporting balanced nervous system activity, particularly in horses prone to stress or excitability.
Magnesium oxide is a highly concentrated inorganic source of magnesium commonly used in equine diets. It provides a bioavailable and cost-effective way to maintain optimal magnesium levels, especially for horses with limited access to fresh forage or those losing electrolytes through heavy sweating or training.
Consult with a nutritionist or veterinarian prior to use.
Top dress once daily on feed or ration.
Body Weight
Scoops
Dose
< 200 kg
½ scoop
15 g
200 – 500 kg
1 scoop
29 g
> 500 kg
1 ½ scoops
44 g
1 scoop = 29.6 cc = 29 grams
Body Weight
Scoops
Dose
< 440 lb
½ scoop
15 g
440 – 1100 lb
1 scoop
29 g
> 1100 lb
1 ½ scoops
44 g
1 scoop = 29.6 cc = 29 grams
Warning / Caution:
A scale should be used with all individual ingredients to ensure accurate dosing.
For equine use only. Not for use in horses intended for food. Keep out of reach of children.
GUARANTEED ANALYSIS: Per gram serving
Nutrient
Concentration
Per 29 g
Magnesium
56%
16
g
Ingredients: Magnesium Oxide 56%
Recommended Use: Supports muscle and nervous system function.
Register & manufactured by: Mad Barn Inc., Petersburg, ON, Canada.
Disclaimer: These statements have not been evaluated by Health Canada or the FDA. This product is not intended to diagnose, treat, cure or prevent any disease.
1 kg (2.2 lb): SKU 628055182009 5 kg (11 lb): SKU 628055182016
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Metric (kg)
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kg
grams
* Recommended serving size of 5.8 grams per 100 kg (220 lb) of body weight
Servings
Cost Per Day
Disclaimer: Recommended feeding rate varies depending on your horse's condition and current diet. Consult with a nutritionist to determine the appropriate inclusion rate for your horse.
Frequently Asked Questions
Magnesium is an essential mineral involved in hundreds of enzymatic reactions in the horse’s body. It helps regulate energy metabolism, nerve transmission, muscle contraction, and bone integrity. Adequate magnesium supports normal muscle function, calm behavior, and overall performance. As a nutritional supplement, magnesium is commonly used to help horses maintain muscle comfort, metabolic balance, and a steady temperament, especially in those with higher demands, exposure to stress, or diets low in magnesium.
Horses most likely to benefit from additional magnesium include those on low-quality forage, horses with metabolic issues such as insulin resistance or PPID, performance horses with higher nutrient demands, and nervous or excitable horses. Senior horses may also benefit if absorption efficiency decreases with age. Magnesium should always be supplemented as part of a balanced diet that meets your horse’s overall nutrient requirements.
Magnesium plays a key role in muscle contraction and relaxation. Low levels may contribute to stiffness, tension, or reduced recovery after exercise. By ensuring adequate magnesium intake, horses are better able to maintain normal muscle function and comfort, especially during work or training.
Magnesium is involved in the transmission of nerve signals. Adequate magnesium helps support a healthy nervous system, which may contribute to a calmer, more focused attitude in some horses. Horses that are easily excitable or stressed are sometimes supplemented with magnesium to help maintain normal behavior and reactivity.
Research in horses has shown that Magnesium Oxide is well absorbed and provides an effective source of elemental magnesium. One study in horses reported 70% bioavailability, which is comparable to other sources studied in horses. Magnesium Oxide also has the highest concentration of elemental magnesium out of commonly used supplement ingredients. This makes Magnesium Oxide one of the most practical and cost-effective sources of magnesium for equine diets.
Some horses may show changes in muscle comfort or attitude within a few days to weeks of magnesium supplementation. In other cases, improvements may take several weeks of consistent feeding. As with any supplement, results vary by horse, and magnesium should be part of a balanced overall diet for best results.
Possible signs of inadequate magnesium include muscle tightness, nervousness, difficulty relaxing, poor performance, or a dull coat. Severe deficiency is rare but may result in muscle tremors, weakness, or irregular behavior. Because these signs can overlap with other nutrient imbalances, diet analysis is the best way to assess magnesium intake.
Forage is the primary source of magnesium in the horse’s diet. However, levels vary depending on soil type and plant maturity. When supplementation is needed, common sources include Magnesium Oxide, magnesium sulfate (Epsom salt), and chelated forms such as magnesium malate or magnesium glycinate. Magnesium Oxide is often preferred because it is well absorbed, economical, and highly concentrated in elemental magnesium.
The National Research Council (2007) sets the minimum requirement for magnesium at about 7.5 g per day for a 500 kg (1,100 lb) horse at maintenance. This represents the level needed to avoid deficiency, but it does not necessarily reflect the optimal intake for health and performance. Many horses benefit from higher levels, especially those in heavy work, lactating mares, or growing horses.
A typical feeding rate for supplementation is around 29 g of Magnesium Oxide per day, which provides approximately 16 g of elemental magnesium for a 500 kg horse. The recommended serving size depends on the magnesium content of the horse's forage and overall diet, so it is best to confirm with a nutritionist or through a diet analysis.
Yes, Magnesium Oxide is safe for horses with Cushing’s (PPID), insulin resistance (IR), and other metabolic issues. It is commonly added to equine diets to support normal metabolic function and insulin sensitivity and can be used alongside prescribed medications such as Prascend® (pergolide). Always consult your veterinarian when making changes to the diet of a horse with metabolic concerns.
Yes, Magnesium Oxide can be used with most common equine medications, including Prascend®, NSAIDs, and ulcer treatments. If your horse is on prescription medication, consult your veterinarian before adding new supplements.
Yes. Each container includes a scoop that holds approximately 29 g of Magnesium Oxide by weight, which provides about 16 g of elemental magnesium. Because serving size requirements can vary, it is recommended to weigh the supplement for accuracy.
Magnesium Oxide is most often top-dressed on feed and can be given dry or mixed with soaked hay cubes, beet pulp, or grains. It can also be made into a paste and syringed if necessary. Horses may receive their daily serving once or divided into two meals, depending on feeding schedule and preference.
Magnesium Oxide is a pure ingredient that contains approximately 56% elemental magnesium by weight. The remainder is oxygen, since Magnesium Oxide is a compound made of both magnesium and oxygen. All supplemental sources of magnesium are bound to another molecule (for example, sulfate, oxide, or malate), so no product can provide 100% pure elemental magnesium. This bound form makes the mineral stable, safe to handle, and usable by the horse’s body.
Yes, Magnesium Oxide can be safely combined with comprehensive vitamin and mineral supplements such as Omneity or AminoTrace+. Omneity generally provides enough magnesium for most horses, though some may respond to additional supplementation. AminoTrace+ already supplies higher magnesium levels, so additional supplementation is rarely needed unless specifically recommended by your veterinarian or nutritionist.
Yes, Magnesium Oxide can be fed with Mad Barn’s Visceral+. However, keep in mind that a standard serving of Visceral+ provides about 5.6 g of magnesium. Some horses may benefit from additional magnesium, but this depends on how much is already being supplied by forage and the rest of the diet. For personalized guidance, consult with a veterinarian or equine nutritionist.
Magnesium Oxide is a concentrated powder, so the serving size is much smaller compared to other forms such as magnesium sulfate, magnesium malate, or magnesium glycinate. Because less volume is required, many horses find it more palatable and easier to accept. In general, most horses consume Magnesium Oxide readily when it is mixed with their regular feed. As with all supplements, individual preferences vary, and Mad Barn offers a 100% Happiness Guarantee to ensure your horse will eat it.
Research in horses has shown that Magnesium Oxide is well absorbed and effective. For example, studies in foals reported absorption of around 90%, and other equine trials confirmed bioavailability of about 70%. Magnesium Oxide also provides approximately 56% elemental magnesium, while chelated forms such as magnesium glycinate contain only 8–20%. Because horses have relatively high daily magnesium requirements, Magnesium Oxide is a practical and efficient source that delivers more usable magnesium per gram. It is also significantly more affordable, making it accessible to a wider range of horse owners.
Our Magnesium Oxide is 100% pure with no fillers or additives. The reason the guaranteed analysis lists 56% is because Magnesium Oxide is a compound made up of both magnesium and oxygen. By weight, only about 56% of the compound is magnesium, while the remaining 44% is oxygen. In nutritional supplements, magnesium is always bound to another molecule, such as oxide, malate, or sulfate, to make it stable, safe to handle, and usable by the horse’s body. Pure elemental magnesium cannot be fed on its own because it is highly reactive and unsafe.
Magnesium oxide is generally very safe when fed at recommended levels. Excess magnesium is usually excreted in urine, but very high intakes can lead to loose manure or digestive upset. Toxicity is rare and typically only occurs with extreme overfeeding. Always measure carefully and follow feeding guidelines.
Magnesium Oxide has a guaranteed shelf life of two years from the date of manufacture, printed on the packaging. Store in a cool, dry location with the container tightly sealed. Avoid exposure to moisture, heat, or direct sunlight to maintain potency.
Ask A Question
Have a question about this product? Ask below and our nutritionists will be happy to assist.
“Adequate magnesium is one of the first things I look for on a hay analysis... It plays a critical role in energy storage, calming excitable nerves and muscle and normal insulin sensitivity.”
Support calm focus, relaxed muscles, and a balanced diet.
Mad Barn's Magnesium Oxide is a concentrated macromineral supplement that helps maintain normal muscle relaxation, nerve signaling, electrolyte balance, metabolic function, and a balanced stress response.
Use magnesium daily to support your horse when they are tense, reactive, tight through the body, working hard, or struggling to stay settled under pressure.
✓Supports normal muscle contraction and comfort
✓Helps horses stay composed under everyday stress
✓Supports post-exercise care in hard-working horses
✓Low cost per serving and easy to top-dress
Why Horses Need Magnesium
Support for Tense Horses & Hard-Working Muscles
Magnesium is an essential macromineral involved in hundreds of enzyme-dependent reactions in the horse's body. It contributes to bone formation, protein synthesis, cellular energy production, electrolyte balance, and normal functioning of muscles and nerves.
Magnesium works closely with calcium to regulate muscle activity. Calcium initiate muscles contraction, while magnesium supports the return to a relaxed state, which is important for normal muscle tone, coordination, and comfort during and after work.
When magnesium intake is low or demand is increased, horses may have a harder time maintaining normal neuromuscular function. This can contribute to tension, poor focus, muscle tightness, or difficulty settling.
Horses get magnesium naturally from forage and feed, but needs increase with exercise, growth, lactation, and heavy sweating. Mad Barn's Magnesium Oxide provides a concentrated source for horses who benefit from additional support during work or periods of increased physiological demand.
56%
Elemental Magnesium
Highly concentrated, so horses need a smaller serving compared to other forms of magnesium such as citrate, sulfate, and many chelates.
70%
Bioavailable in Equine Research
Magnesium oxide has been evaluated in horses and is well-absorbed from the gastrointestinal tract.
29 g
Typical Daily Serving
A 29 g serving provides approximately 16 g of elemental magnesium for a 500 kg (1,100 lb) horse.
$0.24
Affordable Cost Per Day
A single ingredient mineral powder that fits affordably into any feeding program.
Which Horses Benefit Most from Magnesium?
Magnesium Oxide helps support the everyday mineral balance your horse relies on to feel comfortable, focused, and ready to work. Supplementing magnesium can help bring the total diet into an optimal range, supporting horses through training, growth, lactation, and changing nutritional demands.
Tight or tense muscles
Supports normal calcium-magnesium balance in muscle cells, helping horses maintain normal muscle tone, relaxation, and comfort after work.
Reactive or sensitive horses
Adequate magnesium supports normal nerve signaling and a balanced stress response in horses that are tense, distracted, or slow to settle.
Performance horses
Working horses have higher magnesium requirements to support muscle function and replace sweat losses. Supplementation supports post-exercise care and electrolyte balance.
Metabolic horses
Magnesium is involved in insulin signaling and normal glucose metabolism, making adequate intake important in low-NSC feeding programs for easy-keeper breeds.
Hay-based diets
Hay mineral content depends on soil, region, species, and harvest conditions. Magnesium Oxide helps correct low intake identified on a forage analysis.
Reproduction & lactation
Pregnancy and lactation increase mineral demand. Adequate magnesium intake supports normal muscle function, mineral balance, and milk production as part of a balanced diet.
Magnesium Requirements
How Much Magnesium Does Your Horse Need?
The National Research Council (NRC) establishes minimum magnesium requirements for horses based on body weight, workload and physiological status. These values estimate the amount of elemental magnesium needed to prevent deficiency. Exercise increases requirements by raising the demands from muscle activity and adding mineral losses through sweat.
The following requirements are based on mature adult horses. For help formulating a diet for a growing horse, a breeding or lactating mare, or a horse with special care needs, submit your horse's information for a free nutrition consultation.
Daily Requirement
Elemental magnesium in grams per day
Maintenance
1511840
7.5
Maintenance
8.8
Light Work
10.0
Moderate Work
12.5
Heavy Work
250 kg 550 lb400 kg 880 lb550 kg 1,210 lb700 kg 1,540 lb800 kg 1,760 lb
Adequacy target: NRC requirements estimate the minimum magnesium intake needed to maintain normal status and prevent deficiency signs under typical feeding conditions. These values are based on average nutrient availability, and NRC notes that individual horses may require adjustments based on diet, physiological state, and management conditions. Because magnesium is required for neuromuscular signalling, muscle relaxation, electrolyte balance, bone mineralization, and cellular energy metabolism, Mad Barn nutritionists use an adequacy target of 200% of the NRC minimum requirement when additional daily magnesium support is desired.
Why Use Magnesium Oxide?
Your horse needs magnesium for more than staying calm.
Magnesium acts as a cofactor in hundreds of enzymatic reactions, including pathways involved in cellular energy production, neuromuscular signaling, electrolyte balance, bone metabolism, and glucose regulation.
Supporting adequate magnesium intake helps maintain the normal physiology behind muscle comfort, responsiveness, recovery, performance, and metabolic health.
1
Muscle relaxation
Calcium helps initiate muscle contraction. Magnesium helps regulate calcium movement so muscle fibers can return to a relaxed state after contraction.
2
Nerve signaling
Magnesium supports normal ion balance across nerve cell membranes, helping maintain healthy communication between nerves and muscles.
3
Energy metabolism
Magnesium is required for ATP-dependent reactions, supporting the energy pathways active horses rely on during work and recovery.
4
Metabolic support
Magnesium is involved in insulin signaling and normal glucose metabolism, making adequate intake important in low-sugar, low-starch feeding programs.
Magnesium oxide is the most concentrated supplemental form, providing 56% elemental magnesium. Other products require much larger servings and cost many times more per gram of magnesium.
Magnesium oxide provides horses with a palatable, well-absorbed, low-volume, cost-effective source for daily feeding.
✓Provides more elemental magnesium per gram than alternatives
✓70% oral bioavailabilty in equine research studies
✓Less likely than magnesium sulfate to cause loose manure
✓Palatable and easy to add to any feeding program
Comparison
Best Value Magnesium Oxide
Magnesium Sulfate (Epsom Salts)
Magnesium Citrate
Oral absorption
70%
70%
45%
Concentration
56%
10%
16%
Serving size for 15 g magnesium
29 g
140 g
94 g
Cost per 15 g magnesium
$0.24
$0.76
$7.99
Ease of Feeding
Concentrated serving
Large serving May cause loose manure
Large serving High cost per dose
Why Concentration Matters
Magnesium is a macromineral, meaning horses require it in gram-level amounts each day, not trace amounts. A concentrated source provides more elemental magnesium per scoop, making it easier to deliver an effective daily intake without adding unnecessary bulk, bitterness, or cost to the ration.
Signs of Low Magnesium
How Low Magnesium Can Show Up in Horses
When magnesium intake is too low for the horse's needs, signs may show up as muscle tension, sensitivity, excitability, reduced performance, or slower recovery after work. These signs should be considered alongside training, management, and the overall diet.
Magnesium status is evaluated by assessing total dietary intake against the horse's requirement. A nutritionist can calculate magnesium supplied by forage, feed, balancers, and supplements to determine the optimal inclusion level for your horse.
1
Tight or sore muscles
When magnesium is undersupplied in the diet, horses may feel tight through the body, slow to loosen up, sore after work, or less comfortable after exercise.
2
Heightened sensitivity
Magnesium supports normal nerve signaling. When intake is low, some horses may appear more sensitive to touch, sound, pressure, or changes in their environment.
3
Excitability or reactivity
Magnesium supports normal neuromuscular signaling. Horses with low intake may appear more reactive, distracted, tense, or difficult to settle.
4
Poor recovery
Magnesium is involved in electrolyte balance and energy metabolism. Low intake may contribute to reduced performance, poor recovery, or difficulty maintaining normal muscle function during work.
Signs of low magnesium overlap with pain, behavioral concerns, stomach issues, and other medical concerns or nutritional deficiencies. For sudden, persistent, or unexplained changes in your horse's normal behavior or performance, consult your veterinarian.
Customer testimonials
Real results horse owners notice in the barn and under saddle.
Owners most often describe changes in muscle relaxation, reactivity, barn anxiety, sensitivity, body comfort, and overall demeanor when Magnesium Oxide is fed consistently as part of a balanced diet.
★★★★★
Relaxed Focus
"In the short time since I've been using it my horse has been the most focused/patient/relaxed in all the 15 years I've owned him."
Michaela Smet
✓ Verified Customer
★★★★★
Improved Reactivity
"This product made my extremely spooky and explosive gelding way less reactive, highly recommend!"
Tori Korney
✓ Verified Customer
★★★★★
Physical and mental comfort
"This has significantly improved her physical and mental comfort after 4-5 weeks of daily use. I will be keeping her on this as long as I have her!"
Jacqueline Muscat
✓ Verified Customer
★★★★★
Tight muscles
"Our body worker recommended Dolly be put on a Magnesium supplement to help with her tight muscles and I can already see a difference in her."
Lora Muse
✓ Verified Customer
★★★★★
Calm Performance
"This product worked great on our 12 yo Gelding. It provided just the perfect amount of calmness still allowing him to perform at a high level."
Cedric Babineaux
✓ Verified Customer
★★★★★
Quality and Affordability
"Super happy to have found a quality magnesium supplement at a very reasonable price! Fast and free delivery too!"
Magnesium Oxide can be top-dressed onto your horse's feed. It should be fed consistently as part of a balanced, forage-first diet that meets requirements for salt, electrolytes, protein, vitamins, and minerals.
1
Feed Consistency
A typical serving is 29 g per day for a 500 kg (1,100 lb) horse, providing approximately 15 g of elemental magnesium.
2
Evaluate the Full Ration
Forage, grain, and fortified feeds all contribute magnesium. Ensure your horse's overall diet is balanced to support optimal focus, muscle health, and performance.
3
Monitor Response
Evaluate your horse's response over several weeks. Track changes in muscle comfort, recovery, sensitivity, willingness to work, and performance.
Get the best results with a custom feeding plan. Our nutritionists can help you determine the optimal dosage for your horse's diet, workload and individual needs. Submit your horse's diet online for a free analysis.
100% Customer Happiness Guarantee
Try Magnesium Oxide Risk-Free
We're confident you'll love Magnesium Oxide. If you're not satisfied with the product, our team is here to help you find the right solution or provide a full refund.
Less than 1% of customers ever use our satisfaction guarantee.
Need help deciding? Talk to a nutritionist for free before you buy.
Every horse's forage, workload, body condition, age, sweat rate, metabolic status, and current supplement program is different. You should always consult a qualified nutritionist before altering your feed program.
Submit your horse's diet for analysis online.
One of our equine nutritionists will be happy to provide a complimentary review and help determine whether Magnesium Oxide is the right fit for your horse.
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AminoTrace+ 
MagneChrome+ 
Magnesium Oxide 
Omneity® Pellets 
Omneity® Premix 
Performance XL: Electrolytes 
Visceral+ 
