My lab also used IgG2a Rat anti-BrdU from Abcam (Cat. No. AB6326): reacts against mouse and rat. We use it at a 1:500 dilution, and perform antigen retrieval on tissue first before staining.
I don't remember which antigen retrieval protocol was used, but in my folder is one utilizing HCl, and the other method involves pH 6.0 sodium citrate in a vegetable steamer.