Just a guess but to me it looks like proud flesh from an old injury that was allowed to grow too large for skin to grow over it. Greetings and welcome to BYH. Glad you decided to join us. I hope the issue isn't a real "issue" for the cow. Does she seem to get around without issue? Maybe @farmerjan or @greybeard or @jhm47 or one of the other cow folks will take a look and comment. Please browse around and make yourself at home.