I have a herd of 30-50 dairy goats at any given time. My property of 50 acres is about half wooded. 7 or 8 years ago I moved here from a smaller farm and the land was nearly impassable in many places grown up with osage orange and russian olive, briars, and poison ivy in the understory. Now it looks like a park... by autumn each year there's not a scrap of woody vegetation up to about 5 or 6 feet off the ground. The goats will literally stand on each others backs to reach up as high as they can for branches... one will pull it down the rest swarm it and when it comes back up its a bare twig. The goats especially love nuisance plants that other livestock won't eat... anything viney or woody or broadleafed... they play hell on my fruit tree orchard if they get into it... but they are awesome for turning a thick impenetrable forest full of undergrowth into a parklike setting that you can stroll through. And I have not seen a sprig of poison ivy in years! 
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