Which weeds precisely are you needing to get rid of? Ragwort, for best results, really needs to be pulled by hand. If you kill it with weed killer, or cut it, then you are still best advised to go round and pick it up afterwards. Have a ragwort party, all welcome
. We rarely see ragwort here now, just the odd plant blown in on the breeze from the road verges.
Our sheep eat every other weed I can think of, even dockens, spear and creeping thistle, buttercups, and I would have thought they were ok for goats too (but I don't keep goats so don't take my word for it).
In fact we dig out all spear thistles, and mow creeping thistle, either with a topper or the lawn mower, which keeps them in check.
We have just finished digging spear thistle and had filled barely one wheelbarrowful this year, compared to trailerloads a few years ago. Now it's the turn of dockens, which are having the stem scythed off to prevent them seeding, then they will be mown and made with the hay. We will try to dig them out after the hay's in, as it's only one field. I say 'we' but it's not me as I can't turn over soft earth now, let alone dig out deeprooted plants.
I wouldn't use weedkiller of any sort on my land, but then I follow organic principles, unless it's meds for livestock.