Are you sure it's dandruff and not dander? Dander, which will feel waxy, is the natural water repellent to prevent horses from getting soaked to the skin. Some breeds have more than others. I've always boiled whole flax seeds as I had a paper from our ag. Ministry, that states it contains arsenates. Heat changes it to something harmless. The water gets quite mucuousy so I'd add about a 1/2 cup to a.m. And p.m. Feeding.