It probably depends highly on what you feed them...

I think it depends on if you include shipping from Australia to North America in the footprint calculation.

Sheep grazing also strips the land bare of deep and complex vegetation upending whole ecosystems. Perhaps in a futile or misguided gesture I try to keep my consumption of lamb to an occasional treat rather than a regular thing.

Wouldn't this depend on location and source? I used to live in Scotland, where sheep graze on grass in fields that don't really take away space for vegetables (unless you want to survive on potatoes and cabbage), and they're local. So I assumed they're not that bad.