20/02/2026
Fun Fact Friday 🐴
🐴 "Big Head" in horses (scientifically known as Nutritional Secondary Hyperparathyroidism) is a metabolic condition where a horse’s body, desperate for calcium, actually steals it from its own bones.
🐴 The "big head" appearance is caused by the body replacing bone mineral with soft, fibrous connective tissue, which makes the facial bones (specifically around the nasal bone and upper jaw) appear swollen.
🐴 In the past, it was called "Bran Disease" or "Miller’s Disease" because it was commonly seen in horses fed high-bran diets by flour millers.
🐴 Only about 5–10% of horses affected by the underlying calcium deficiency ever show the dramatic facial swelling. Often, the first sign is a unexplained, shifting lameness or, unfortunately, a broken bone.
🐴 It is frequently caused by grazing on tropical or sub-tropical grasses (like Setaria, Kikuyu, and Buffel grass) that are high in oxalates. These oxalates bind to calcium in the gut, preventing the horse from absorbing it.
🐴 Symptoms typically develop after 2 to 8 months of grazing on high-oxalate pastures.
🐴 While the facial bones can return to normal, it can take 4 to 12 months of specialised dietary treatment (usually high-dose calcium supplements like calcium carbonate or lucerne) for the bones to fully re-mineralise.
🐴 Young, growing horses are more likely to develop the dramatic swollen facial look because their bones are still developing, while older horses may only show signs of stiffness or joint pain.
