Anyone grow Mangles for their goats for example - looked really easy to grow.[/quote]
There's lots of stuff you can grow to feed livestock...I'm not sure of the food value of mangles(expect it's quite high)but they need quite good conditions,if your land is exposed you might fare better with fodder beet,you can graze off the tops(sheep,or else cut them by hand and feed)then lift and store the roots in a clamp.
As you'll know ,the ''goats eat anything'' is a bit of a myth,they will nibble at stuff enough to destroy it,but they are quite particular about what they eat. Field beans are easy and a VG protein source to add to their cereal.As above you can grow hay and best of all haylage,but we did experiment with Lucerne,it wasn't a great success,but our place was at nearly 1000ft,I know of other goat keepers that have had great success with it.
Most of the seed for the above stuff should be available in reasonable quantities from a seed merchant that serves both gardener and farmer,eg Tuckers.