What is Big Head in Horses?
Big Head in horses (Equine Nutritional Secondary Hyperparathyroidism) is caused by long-term calcium deficiency – often due to grazing on oxalate-rich pastures that block calcium absorption. A calcium-to-phosphorus dietary intake ratio below 1:1 (especially below 0.5:1), increases your horse’s risk of developing this disorder – resulting in calcium being pulled from bones in order to stabilise blood levels. Symptoms include illness, lameness, and swelling of the facial bones, creating the appearance of an enlarged head – and if left untreated, can lead to permanent bone damage & significant health problems.
The Calcium Connection
Did you know some common Australian grasses can steal calcium from your horse’s diet, leading to serious bone problems? If your horse grazes on sub-tropical pastures, you’ll want to read on!
Why Does Calcium Matter?
Calcium is a major player in your horse’s health. It’s not just about strong bones—calcium also helps muscles contract, nerves send signals, and blood clot properly. Your horse’s bones store a backup supply, keeping a careful balance with phosphorus (around a 2:1 ratio). But some pastures can disrupt this balance, making calcium hard to absorb.
When a horse eats certain sub-tropical grasses for too long without extra calcium, they can develop Nutritional Secondary Hyperparathyroidism (NSH), also called Big Head. This painful condition happens when the body pulls calcium from the bones, weakening them—especially in the face and skull.
The Hidden Danger in Some Grasses
The problem? Oxalates. These are natural compounds in some grasses that latch onto calcium in the gut, making it impossible for the horse to absorb properly. The bound-up calcium passes through the digestive system without being used, leaving the horse calcium-deficient.
Common High-Oxalate Grasses in Australia:
- Buffel Grass
- Green Panic Grass
- Kikuyu Grass
- Pangola Grass
- Para Grass
- Setaria Grass
- Signal Grass
Horses grazing on these grasses for one month or more without a proper calcium supplement are at a higher risk of developing Big Head.
What Happens to Horses with Big Head?
When calcium levels drop too low, the horse’s body goes into emergency mode. The parathyroid gland releases a hormone that pulls calcium from the bones to keep the blood levels steady. Over time, this weakens bones, especially in the face, causing swelling and deformities.
Signs Your Horse Might have Big Head:
- Stiff or sore joints
- Tenderness when moving
- Loss of muscle condition
- Swollen jawbones
- Loose teeth
If left untreated, Big Head can lead to permanent bone damage and difficulty eating.
How to Protect Your Horse From Nutritional Secondary Hyperparathyroidism (NSH)
The good news? Big Head is preventable with the right diet!
Adding a highly absorbable calcium supplement is the key to balancing out oxalates and keeping your horse’s bones strong. CEN Grain Free Ultimate and CEN CF50 contain marine calcium (red-algae – Lithothamnion), which has excellent bioavailability, meaning your horse can absorb and use it effectively.
Best Feeding Strategy:
- Feed a daily hard feed with CEN Grain Free Ultimate or CEN CF50 to provide extra calcium. (This helps prevent oxalates from binding to calcium during digestion.)
- If already feeding CEN Grain Free Ultimate or CEN CF50 and CEN XtraBalance, increase amounts depending on horse’s requirements.
- If moderate to severe – replace 1-2 biscuits of the high oxalate roughage with lucerne hay
- Horses need a calcium-to-oxalate ratio of at least 0.5:1 to stay in balance. If the ratio falls below this, calcium stored in the bones will start to be pulled out, leading to Big Head.
A normal adult horse requires 25-30g of calcium per day (without oxalates in the diet).
General ‘Big Head’ Disorder recovery times:
- Mild cases (early stages): 6-12 weeks with proper calcium supplementation. Horses typically regain normal bone metabolism within this period, though some symptoms (like mild swelling) may take longer to fade.
- Severe cases (significant bone changes): 6-12 months or more. If facial swelling and bone deformation are present, recovery takes longer. Some changes, like facial bone expansion, may be permanent, even if the horse regains normal calcium levels.
Factors affecting a horse’s recovery:
- Diet Correction: Providing a highly bioavailable calcium source (e.g., marine calcium in CEN Grain Free Ultimate or CEN CF50 or CEN XtraBalance) ensures faster absorption.
- Phosphorus Balance: Keeping calcium-to-phosphorus ratios around 2:1 prevents further bone loss.
- Early Intervention: The sooner treatment starts, the better the recovery. Horses with long-term Big Head may have irreversible bone damage.
- Veterinary Support: Severe cases may need X-rays and monitoring to track bone density improvements.
Signs of improvement:
- Reduced facial swelling (if present)
- Improved movement and joint comfort
- Better coat and muscle condition
- Stronger teeth and jaw stability
By understanding the risks of high-oxalate pastures and providing the right supplements, you can keep your horse’s bones strong and healthy – no swollen heads here!
Written By Bryan Meggitt (BMedSc. PGCrtMedSc.)
Blood Scientist and Co-founder of CEN Horse Nutrition