Big Head Disease in Horses by a Vet – 2025 Guide to Nutritional Secondary Hyperparathyroidism & Calcium Balance 🦴🐴
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Big Head Disease in Horses by a Vet – 2025 Guide to Nutritional Secondary Hyperparathyroidism & Calcium Balance 🦴🐴
By Dr Duncan Houston, BVSc
Introduction
“Big Head Disease” may sound like a strange or rare condition, but it's a serious nutritional disorder officially known as Nutritional Secondary Hyperparathyroidism (NSH). In 2025, equine vets continue to diagnose this condition in horses consuming unbalanced diets—particularly those high in phosphorus or grazing on oxalate-rich grasses. The result is calcium being pulled from the bones, replaced by fibrous tissue, and often a visibly enlarged skull. Understanding the dietary causes, early signs, and corrective measures can help prevent this painful and sometimes irreversible disease.
What Is Nutritional Secondary Hyperparathyroidism (NSH)? 🧬
- A condition caused by imbalanced dietary calcium and phosphorus
- Low calcium or high phosphorus diets trigger parathyroid hormone (PTH) release
- PTH stimulates the body to draw calcium from bones
- Bone loss is replaced with fibrous tissue—especially in the head and jaw
Why It’s Called Big Head Disease 🦷
- Fibrous tissue buildup causes the bones of the skull to swell
- This gives the head an enlarged, disfigured appearance
- In advanced cases:
- Teeth loosen and fall out
- Horses struggle to chew or graze
- Bone fractures and lameness may develop
Causes of NSH in Horses ❌🍽️
1. Improper Calcium-to-Phosphorus Ratios
- Horses require a diet with a Ca:P ratio of 1.5:1 to 2:1
- Feeding grains high in phosphorus without calcium balance is a key trigger
2. Oxalate-Rich Grasses 🌿
- Oxalates bind calcium in the gut, preventing absorption
- Grasses that pose risk:
- Buffel grass
- Dallis grass
- Setaria
- Panic grass
3. Low Vitamin D
- Vitamin D supports calcium absorption
- Deficiency may contribute to NSH, especially in stabled horses with limited sun exposure
Early Signs of Big Head Disease 🔍
- Shifting leg lameness
- Stiff gait
- Enlargement of facial bones or mandible
- Tooth loosening or loss
- Reduced appetite or difficulty chewing
- In extreme cases, facial deformity and poor body condition
Diagnosis 🩺
- Physical exam and visual facial asymmetry
- Bloodwork showing low calcium or high phosphorus
- Radiographs showing bone thinning or fibrous changes
- Feed analysis for Ca:P ratio or oxalate content
Treatment & Recovery Plan ✅
1. Immediate Diet Change
- Switch to alfalfa-based forage (high in calcium)
- Stop grain feeds unless properly balanced with calcium
- Avoid grazing on known oxalate-rich grasses
2. Calcium Supplementation
- Add calcium carbonate (limestone) to feed
- Also consider calcium lactate or dicalcium phosphate as alternatives
3. Time and Monitoring
- Recovery may take 6–12 months depending on severity
- Teeth may not regrow; hoof and joint care may be needed
Preventing Big Head Disease 🛡️
1. Balance All Feeds
- Ensure 1.5–2:1 calcium to phosphorus ratio
- Use nutrition calculators or consult with a vet
2. Avoid Oxalate Grasses or Supplement Calcium Accordingly
- If oxalate pasture is the only forage available, supplement with alfalfa or calcium
3. Watch for Early Signs
- Facial swelling, gait changes, appetite drop
- Annual dental and dietary reviews are essential
Case Example: Gelding on Buffel Grass with Jaw Swelling
- 9-year-old gelding developed lower jaw swelling and shifting lameness
- Diet included buffel grass and grain with no added calcium
- Bloodwork showed high phosphorus and low calcium
- Switched to alfalfa hay with calcium carbonate supplement
- Swelling reduced over 6 months; lameness resolved
FAQs About Big Head Disease in Horses
Q: Is Big Head Disease reversible?
A: In early stages, yes. With diet correction, many horses recover over 6–12 months.
Q: Can it happen on pasture alone?
A: Yes—especially if the pasture contains oxalate-rich grasses or is nutrient deficient.
Q: Is this condition painful?
A: Yes. Bone loss and facial pressure are painful and can make eating difficult.
Conclusion
Big Head Disease, or nutritional secondary hyperparathyroidism, is a preventable but serious condition in horses tied to dietary calcium imbalance. In 2025, awareness of forage composition, calcium ratios, and high-oxalate grasses is more important than ever—especially for horses in tropical or subtropical regions. Prevention through nutrition is key to keeping your horse’s bones strong and face-free of deformity.
Need help analyzing your horse’s feed or pasture risk? Visit AskAVet.com or download our app 📱 to consult Dr Duncan Houston for customized calcium and forage planning. 🩺🐴
