38. Danger in the Grass: High-Oxalate Pastures, Calcium Deficiency & Bighead Disease in Horses

In this episode of the Happy Horse Nutrition Podcast, Dr Nerida tackles a pasture risk that catches many good horse owners out: high-oxalate warm-season grasses that can block calcium absorption, slowly weaken bone, and set horses up for nutritional secondary hyperparathyroidism (Bighead disease). You’ll learn the simple physiology behind it (the “bone calcium bank” concept), why blood calcium can look normal even when bones are being depleted, and the real-world signs that are easy to misread; shifting lameness, sore or grumpy behaviour, odd gait, skull changes, loud breathing noise under work, dental issues and poor hoof quality. Nerida walks you through practical pasture ID tips for the big culprits—kikuyu, buffel, couch/bermudagrass, and the high-risk one: setaria! And explains how oxalate levels and risk change with growth stage and location (including cooler regions in summer). Finally, she outlines prevention: targeting a calcium: oxalate ratio of at least 0.5:1, keeping calcium balanced with phosphorus and magnesium, why lucerne/alfalfa helps on multiple fronts, and when it’s smarter to use a properly formulated balancer or get expert help… especially if setaria is involved.✅ Want help checking whether your horse’s diet is actually balanced for these pastures (without doing the maths)? Download the MyHappy.Horse app: https://apps.apple.com/app/myhappy-horse/id6633422324❤️ If this episode helped, please follow the podcast on Apple Podcasts/Spotify and share it with a horse owner in warm, wet coastal regions (or anyone feeding teff or bermudagrass hay). 🕖 Until next time… go have a quick paddock walk! Your feed room decisions should always start with your grass. 🌱🐴