If you planted up the swales densely with fodder plants and then fenced it so that the goats could just reach them to eat... like hedgerows - would that work?
Dont forget to add rocks for them to either walk over or jump all over, it helps keep their hooves in good shape.
Maybe these could be added to the swales.
Having kept goats for years in the Southeast (USA), I've found that given enough wild land to browse and graze in, they will balance their own diet pretty well, at least enough to reproduce and raise offspring. This wild forage does include some concentrated foods. Once I remember them disappearing day after day, only to find them diligently eating acorns off the ground from under a certain tree. Turned their droppings an odd color is all I recall from the incident. But surplus milk production, over and above what kids need to grow, benefits from some supplements, unless perhaps they have an unusually rich ecosystem to browse in. Part of the purpose of these supplements is to attract them into the milking area at a given time and keep them occupied on the milking stand. Traditionally this is often grain but I've found it can be whatever happens to be lying around in surplus: excess sweet potatoes, winter squash or pumpkins cut into chunks, apples, celery; the peels of onion, garlic, and even citrus (the gut of a goat seems to be the one thing in nature that can quickly break down citrus peel...even compost has problems with it!)....and my default....movie-theater dumpster popcorn (also my poultry's favorite)!!
I agree with "adiantum's" post. Grain or concentrate feed can be useful for getting them to go where you need them to go. We have been keeping goats for 20 years and I always have something at hand, e.g. organic oats or organic feed pellets "to keep them sweet", say a cupful per head and to lead them to temporary pasture areas and back.
They do not need it. Commercial enterprises would feed quite significant amounts of grains or concentrates simply to increase milk yield and be (more) profitable. Our own approach is "they give what they give". Ours mostly graze, but we have planted a lot of trees for shelter and other uses that double up as fodder trees and we cut a lot for them from late summer onwards (after bird nesting season is finished) to supplement their diet. What they leave behind is used for firewood, stakes, kindling and mulch (shredded).
Incidentally, a friend of mine in Germany who is the Head of a State Institute for Organic Farming has done some really interesting work on goat farming.
The institute has a herd of 80 dairy goats. Their aim is to provide optimum nutrition and animal welfare, work organically, be profitable and reduce concentrate feeding.
If you look at
you can see a system they've been trialling: fodder hedges that are browsed once every three years. The remaining wood is coppiced and used for heating, then the hedge regrows and is fenced off until the next rotation. Importantly, these hedges were planted specifically for the goats. Old hedges (some hundreds of years old) which are of major conservation importance, an integral part of the cultural landscape in that region, and host high biodiversity are not browsed.
They are also doing research on the anthelmintic properties of willows.
He wrote an interesting paper a few years ago on the nutrient value of trees and shrubs for ruminants. It's in German with an English abstract (which I can't copy out of the pdf).
Rahmann, Gerold (2004)
Gehölzfutter - eine neue Quelle für die ökologische Tierernährung.
Landbauforschung Völkenrode - Sonderheft, Band 272, Seiten 29-42, deutsch
Last Spring he gave a paper in Malaysia:
Georg, Heiko; Sporkmann, Katrin; Bender, Sophia; Ude, Gracia; Rahmann, Gerold (2012)
"Feed less Food" - Effect of a low concentrate diet on milk quality, milk fatty acid composition and performance of dairy goats.
In: Proceedings of the 1st Asia Dairy Goat Conference, Kuala Lumpur, Malaysia, 9-12 April 2012.
I can't find it online (yet). But when I last spoke to him he said, if I remember correctly, that they have managed to roughly half the amount of concentrates customarily fed to dairy goats in commercial settings in Germany without compromising on milk yield.
Well I have just seen that goats basically fed upon grasses and leaves and produce milk. By reading the posts above I came to know that they eat mulberry leaves as well as fenugreek seeds. These have been the reason for their source of milk. Well it's not all the time you need to feed the goats. Just for the milk production you can give your goats whatever you want.