I purchased some passes to capture mares for my SD program, but the capture page lists all of my barns as full; they don't show at all.

I've tried clearing my cashe and my site data, my barns still don't show up. I'm very confused.

It's not a bug. You only have pastures and you can't capture horses without barns. I can't remember why but you can't directly capture into pastures

Because when taming a wild horse you want them in a small area. You dont want to turn a bunch of wild horses together in a 100 acre pasture when you are trying to tame them. :P

Oh, that explains it, thank you.