My sister showed a shorthorn heifer that was completely blind in one eye and partially blind in the other. The heifer never had any problems showing. We kept her after we her show career until she was twelve years old.
I have two heifers that both need their hooves trimmed, but I have heard that if you put them on a table to trim hooves they can lose their calf. They are both about 4 months along and are going to the fair in about a month.