Unless there is an antibody with a specific epitope that is recognized and expressed in all species, there really isn't anyway of doing it short of purifying the protein from each species and measuring the amount. If your antibody recognizes all species with equal affinity (a fairly rare event) you are ok, but otherwise not. Sorry to bear such bad news.
I would look at the epitope of the antibody. If this is binding to a conserved region in your protein you can do simple Western Blots. Instead you have to measure the concentration (amount) of your protein by using ELISAs. With ELISAs you will get the concentrations of your protein and you can compare the concentrations. But be careful, if the ELISA is really adequate for different species. Much success! Andreas
Although the epitope may be the same, the surrounding amino acids may alter binding affinity, which would mess up any quantitation. If you can get hold of purified protein from each species and do an elisa on known amounts as Andreas suggests then you may have a fighting chance.