Manganese in Horse Nutrition: Roles & Deficiency Signs

Why Manganese Matters in Your Horse's Diet

Manganese is one of those trace minerals that rarely makes the headlines, yet it plays a quietly critical role in keeping your horse healthy. From building strong bones and cartilage to supporting reproductive health and energy metabolism, manganese is involved in processes your horse depends on every single day.

Despite its importance, manganese is one of the most commonly under-supplied minerals in equine diets — particularly for horses grazing on certain soil types or eating hay-only diets. Understanding what manganese does, how much your horse needs, and what happens when it's lacking can help you make smarter feeding decisions.

Let's take a deep dive into manganese in horse nutrition.

What Is Manganese and Why Do Horses Need It?

Manganese (Mn) is a trace mineral, meaning horses need it in relatively small amounts compared to major minerals like calcium or phosphorus. But "small amounts" doesn't mean "unimportant." Manganese serves as a cofactor or activator for dozens of enzymes in the body, meaning those enzymes simply can't do their jobs without it.

Here are the key biological roles manganese plays in the horse:

1. Cartilage and Joint Health

Perhaps the most well-known role of manganese in horses is its contribution to cartilage formation. Manganese is essential for the production of chondroitin sulphate, a major structural component of cartilage. Without adequate manganese, cartilage quality can deteriorate, potentially leading to joint problems.

For performance horses, breeding stock, and older horses with wear-and-tear on their joints, this function alone makes manganese a mineral worth paying attention to.

2. Bone Development and Integrity

Manganese is critical for proper bone formation, especially in growing horses. It activates enzymes involved in the synthesis of bone matrix — the structural framework that gives bones their strength. Deficiency during growth phases can lead to skeletal abnormalities that may have lifelong consequences.

3. Carbohydrate and Fat Metabolism

Manganese activates enzymes involved in energy metabolism, including those that process carbohydrates and fats. Horses in work, growing youngsters, and lactating mares all have heightened energy demands, and manganese ensures these metabolic pathways run smoothly.

4. Antioxidant Defence

Manganese is a key component of the enzyme manganese superoxide dismutase (MnSOD), one of the body's primary antioxidant defences. This enzyme neutralises harmful superoxide radicals produced during normal metabolism and exercise. Without sufficient manganese, oxidative stress can increase, contributing to cellular damage, inflammation, and slower recovery after exercise.

5. Reproductive Function

In both mares and stallions, manganese supports reproductive health. It plays a role in hormone production and has been linked to normal oestrous cycling in mares and sperm quality in stallions. Breeding operations should be particularly attentive to manganese status in their horses' diets.

6. Wound Healing and Connective Tissue Repair

Manganese supports the formation of collagen and other connective tissue proteins. This means it's involved in wound healing, tendon and ligament integrity, and the general maintenance of skin, hooves, and other connective tissues.

How Much Manganese Does a Horse Need?

The National Research Council (NRC) suggests a minimum manganese intake of approximately 40 mg per kg of total diet dry matter for horses. For a 500 kg horse eating around 10 kg of dry matter per day, that works out to roughly 400 mg of manganese per day as a minimum.

However, many equine nutritionists recommend higher intakes for certain categories of horses:

• Growing horses: 60–80 mg/kg of diet dry matter
• Performance horses: 50–80 mg/kg of diet dry matter
• Breeding horses: 50–70 mg/kg of diet dry matter

These higher recommendations reflect the increased demands placed on manganese-dependent processes during growth, exercise, and reproduction.

Manganese toxicity is extremely rare in horses. The mineral has a very wide safety margin, and horses are quite tolerant of intakes well above the minimum requirement. This makes supplementation relatively low-risk compared to some other trace minerals.

Common Sources of Manganese for Horses

Manganese is found in varying amounts in common equine feedstuffs. Here's where your horse might be getting it from:

Forages

Forages are typically the primary source of manganese in a horse's diet, but concentrations can vary enormously depending on soil type, plant species, and growing conditions.

• Grass hay and pasture typically contain between 40 and 200 mg/kg of dry matter, though some can be significantly lower.
• Legume hays (such as lucerne/alfalfa) often have lower manganese levels than grass hays.
• Soil pH has a significant influence: acidic soils tend to make manganese more available to plants, while alkaline or heavily limed soils can result in forages with very low manganese content.

Grains and Concentrates

Most cereal grains (oats, barley, maize) contain relatively low levels of manganese — typically between 15 and 40 mg/kg. This means that horses on high-grain, low-forage diets may be at higher risk of inadequate manganese intake.

Commercial Feeds and Supplements

Many commercial horse feeds and balancers include supplemental manganese, usually in the form of manganese sulphate, manganese oxide, or organic (chelated) manganese. Organic forms are generally considered to be more bioavailable, meaning the horse can absorb and use them more efficiently.

If your horse is on a forage-only diet without a balancer or mineral supplement, there's a real chance manganese intake could be below requirements — especially if the hay was grown on alkaline soils.

Signs of Manganese Deficiency in Horses

True, severe manganese deficiency is relatively uncommon in horses, but marginal or subclinical deficiency may be more widespread than many owners realise. Because the signs can be subtle and overlap with other conditions, manganese insufficiency often goes undetected.

Here are the key signs to watch for:

Skeletal Abnormalities in Foals and Young Horses

Manganese deficiency during growth can result in:

• Enlarged joints
• Shortened or crooked limbs
• Stiffness and reduced range of motion
• Developmental orthopaedic disease (DOD)

These problems arise because cartilage and bone formation are compromised when manganese is insufficient. If you're dealing with unexplained limb deformities or joint issues in youngstock, it's worth investigating the mineral profile of the diet.

Poor Cartilage Quality and Joint Problems

In adult horses, long-term marginal manganese intake may contribute to:

• Increased susceptibility to joint injuries
• Slower recovery from joint-related issues
• Premature wear of articular cartilage

While manganese deficiency alone may not cause arthritis, it can be a contributing factor, especially in horses already predisposed to joint problems through workload or conformation.

Reproductive Issues

Mares with inadequate manganese intake may experience:

• Irregular or absent oestrous cycles
• Reduced conception rates
• Increased risk of early embryonic loss

Stallions may show reduced libido or decreased semen quality. If your breeding programme is experiencing unexplained fertility issues, a mineral analysis of the diet is a sensible step.

Poor Hoof and Coat Quality

Because manganese supports connective tissue and collagen synthesis, deficiency may manifest as:

• Weak, brittle hooves
• Slow hoof growth
• Dull, lacklustre coat

These signs are non-specific and could indicate deficiencies in other nutrients too (such as biotin, zinc, or copper), but manganese should be on the list of suspects.

Impaired Glucose Tolerance

Some research suggests that manganese plays a role in insulin function and glucose metabolism. While this area needs more study in horses specifically, there's a theoretical link between manganese insufficiency and metabolic dysfunction, which could be relevant for horses prone to insulin dysregulation.

Increased Oxidative Stress and Slow Recovery

Performance horses with marginal manganese status may show:

• Slower recovery from hard work
• Increased muscle soreness or stiffness
• Greater susceptibility to exercise-related tissue damage

This is linked to the impaired function of manganese superoxide dismutase, the antioxidant enzyme mentioned earlier.

Factors That Increase the Risk of Manganese Deficiency

Several factors can put your horse at greater risk of inadequate manganese intake:

• Forage grown on alkaline or heavily limed soils — manganese availability to plants drops significantly as soil pH rises above 6.5.
• High-iron diets — excess iron can compete with manganese for absorption in the gut, effectively reducing how much manganese the horse can utilise.
• High-calcium diets — very high calcium intake (for example, from heavily lucerne-based diets) may also interfere with manganese absorption.
• Forage-only diets with no mineral supplementation — without a balancer or targeted mineral supplement, many hay-based diets fall short on manganese.
• Sandy or mineral-poor soils — some regions naturally produce forages with low trace mineral content.

How to Ensure Your Horse Gets Enough Manganese

The best approach starts with knowing what's actually in your horse's diet. Rather than guessing or blindly supplementing, consider analysing your horse's diet to identify any gaps in manganese or other trace minerals. This allows you to supplement precisely and avoid creating imbalances.

Here are practical steps to ensure adequate manganese intake:

Get Your Hay Tested

A forage analysis will tell you exactly how much manganese your hay contains. This is the single most valuable piece of information for building a balanced diet, since forage makes up the majority of most horses' intake.

Use a Quality Balancer or Mineral Supplement

If your forage is low in manganese, a well-formulated balancer or loose mineral supplement can fill the gap. Look for products that include manganese in an organic (chelated) form for better absorption. Common organic forms include manganese proteinate and manganese amino acid chelate.

Be Mindful of Mineral Interactions

If your horse's diet or water supply is high in iron (which is very common), this could be reducing manganese absorption. Addressing iron overload — for example, by filtering high-iron water or avoiding iron-fortified supplements — can indirectly improve manganese status.

Consider Individual Needs

Growing horses, breeding stock, performance horses, and senior horses may all benefit from manganese intakes above the NRC minimum. Tailor your supplementation to the individual horse's life stage and workload.

Manganese Supplements: What to Look For

When shopping for manganese supplements, you'll encounter several forms:

Organic forms are generally preferred because they're better absorbed and less likely to be affected by mineral antagonisms in the gut. However, inorganic forms like manganese sulphate can still be effective, especially when fed at appropriate levels.

Key Takeaways

• Manganese is essential for cartilage formation, bone health, antioxidant defence, energy metabolism, and reproduction in horses.
• Deficiency signs include skeletal problems in young horses, joint issues, reproductive difficulties, poor hoof quality, and slow recovery from exercise.
• Forage is the primary dietary source, but manganese content varies widely depending on soil type and pH.
• High iron or calcium intake can impair manganese absorption.
• Most horses benefit from a balancer or mineral supplement that includes manganese, especially if forage hasn't been tested.
• Organic forms of manganese are more bioavailable and generally recommended.

Manganese may not be the flashiest mineral in equine nutrition, but it's one your horse can't afford to go without. By understanding its roles and keeping an eye on your horse's diet, you can help prevent the subtle but significant problems that come with inadequate intake.

If you're unsure whether your horse is getting enough manganese — or any other essential nutrient — start by taking a close look at the total diet. Small adjustments now can prevent bigger problems down the road.