Hi Littlestone,
Just out of interest, why did you pick Meikle Findowie as one of your examples? The stones there are very small and to my mind wouldn't have been much use for keeping in livestock.
I don't discount more utilitarian uses, as I think it's very unlikely that all stones and circles were used for the same thing, but I have read before that if a site had been used for holding livestock then there would have been evidence of this in the archaeology.
Cheers
Andy