by Dr Derek Cuddeford,  Royal (Dick) School of Veterinary Studies, University of  Edinburgh The basic feed of horses is forage and what is in it depends on its age. For example young spring grass is mostly water (~85%) and the bulk of the remainder is soluble carbohydrate and protein with little indigestible fibre so it has a high feed value. As the plant material ages the protein and water content decline whereas the indigestible fibre (lignified cell wall material) increases; there is a reciprocal relationship between protein and lignified fibre. Whether it is grass in the field or hay or silage,...