can we use ELISA methods on cow s immunoglubolines equal we use on human Ig?

It depends on the ELISA method you are trying to use and the antigen of interest. In the most basic sense if the cow Ig also predictable the antigen in cross-examine, then it would be possible to use a human-designed assay next to cow antibody. There is also no reason a bovine-specific ELISA assay couldn't be developed.
Yes, you of late have to own the right antibodies. If you are trying to detect if cows make antibodies against a exceptional antigen, you would spot that antigen on a plate, use cow serum as the primary antibody and a labled anti-cow IgG as a secondary antibody.
The easier said than done part maybe would be finding the secondary anti-cow antibody. You can google it though.