From an article by Lindsay Whistance, Organic research centre.
Lots of us on TAS now feed our livestock trees, branches and tree fodder. This is the first article I've seen about it and I find this practice is included in 'agroforestry'.
Traditional fodder trees are: ash, elm and holly
Readily browsed: willow, poplar, rowan, hazel, oak, hawthorn
Less palatable but edible: birch, beech, alder
Poisonous: yew, box
Condensed Tannins (CTs) occur in many leaves (eg oak and willow). Initially they inhibit protein uptake in the rumen, but are then broken down in the abomasum to deliver a high quality protein to the small intestine.
CTs are also an effective gastrointestinal ie gut parasite control, to which worms cannot develop any resistance.
Because tree roots go much deeper than grass roots, they bring a wide variety of minerals into their leaves and bark.