Big Head Disease, also known as Nutritional Secondary Hyperparathyroidism (NSH) occurs when a horse suffers a prolonged calcium deficiency. In response, the body draws calcium from the bones, replacing it with fibrous tissue. This weakens the skeleton and often causes a swollen facial appearance, hence the name "Big Head." A hallmark symptom is a shifting lameness that moves from one leg to another.
Without intervention, Big Head affects the entire skeletal system, making it a serious and painful condition for horses.
What Causes Big Head in Horses?
1. Oxalate-Rich Tropical Pastures
One of the most common causes of Big Head is grazing on sub-tropical grasses that contain high levels of oxalate. Oxalate binds to calcium in the gut and prevents its absorption.
High-risk pasture grasses include:
- Buffel grass
- Setaria
- Kikuyu
- Green panic
- Para grass
- Pangola grass
- Guinea grass
- Signal grass
- Purple pigeon grass
Horses grazing these pastures are at risk of developing a calcium deficiency over time.
2. High-Phosphorus Diets
Feeds that are high in phosphorus and low in calcium, such as cereal grains and grain by-products like wheat bran and mill run, can interfere with calcium absorption. When the calcium-to-phosphorus ratio (Ca:P) is unbalanced, calcium is poorly absorbed, leading to deficiency.
This is especially common in horses on grain-heavy, low-roughage diets, often referred to as Miller’s Disease.
3. Phytic Acid in Feeds
Phytic acid, found in large amounts in wheat bran and other cereal by-products, also binds to calcium in the digestive system, blocking absorption and compounding the deficiency.
Is Your Horse at Risk of Big Head?
You should be concerned if your horse:
- Grazes tropical pastures like buffel, setaria, or kikuyu
- Lives in northern or coastal Australia
- Eats a grain-heavy diet or large amounts of grain by-products
- Shows signs of facial bone enlargement
- Suffers from unexplained or shifting lameness
How to Prevent Big Head in Horses
1. Supplement With Available Calcium
The key to prevention is ensuring the horse receives enough bioavailable calcium to offset the effects of oxalates, phosphates, and phytates.
This can be achieved by:
- Feeding high-calcium, low-oxalate forages like lucerne (alfalfa) and temperate grass hay
- Adding calcium supplements such as limestone (calcium carbonate) and dicalcium phosphate
- Selecting calcium-fortified feeds specifically designed for horses grazing sub-tropical pastures
Suggested dosage:
Add 30g/day of limestone and 30g/day of dicalcium phosphate per 100kg of body weight
2. Choose Balanced Feeds
Supplements like GoStance, Equilibrium Mineral Mix are scientifically formulated with bioavailable calcium, balanced phosphorus, and controlled NSC (non-structural carbohydrate) levels to prevent metabolic issues while maintaining skeletal health.
3. Professionally Balance the Diet
Avoid over-supplementing calcium, especially in young or performance horses, as excess calcium can unbalance the diet. For peace of mind, consider a professional diet analysis such as Truguide .
Can Big Head Be Reversed?
Yes, in many cases, you can reverse early symptoms of Big Head through dietary changes:
- Remove the horse from tropical pastures and high-grain diets if practicable
- Provide lucerne hay and temperate pasture
- Supplement with limestone and dicalcium phosphate or formulated supplements such as GroStance or Equlibrium Mineral Mix
- Ensure the overall diet is balanced, especially in terms of Ca:P ratio
In severe cases, where the horse shows signs such as poor muscle control, calcium injections may be used short-term under veterinary supervision. However, long-term recovery depends on dietary correction, not injections.
Common Myths About Big Head Disease
- "A bit of lucerne will prevent Big Head."
Incorrect. While lucerne helps, it does not provide enough calcium on its own to offset the oxalate load from tropical grasses.
- "Vitamin D injections cure Big Head."
False. Vitamin D helps absorb calcium, but without dietary calcium present, it won’t help prevent or treat Big Head.
- "Dolomite is the best calcium source."
Not true. Limestone and dicalcium phosphate offer much higher calcium bioavailability than dolomite (calcium magnesium carbonate).
- "Injecting calcium cures Big Head." Only temporarily. Calcium injections may stabilise blood calcium levels in emergencies, but they don't fix the underlying bone calcium loss. Ongoing dietary changes are essential for recovery.
Stance Suggestion: Big Head Is Preventable
Need Help?
If you suspect your horse is at risk, or is already showing signs of Big Head, contact Stance Equine for a free diet analysis. Our team can help design a feeding plan tailored to your horse's needs and pasture conditions.
