I am sure I can help you on this one, ring me - evenings ! - on 01647 231456.
One thing to point out immediately, horse coarse mix is desperately low in protein for a goat. Goats need around 16 - 18% protein !!
Another problem which can cause apparent malnutrition is lack of minerals but in particular copper. Ad lib hay, worming etc will all help but the right feed is paramount.
I feed all mine on cattle dairy nuts which contain the right amount of various minerals, inc copper, for a dairy animal. Goats actually need the same amount of copper as a cow, but some areas are very high in molybdenum which prevents the uptake of copper - needless to say, hay produced locally will also be short of copper.
Look forward to hearing from you,